白话学习MVC(九)View的呈现一

一、概述

　　本节来看一下ASP.NET MVC【View的呈现】的内容，View的呈现是在Action执行之后进行，Action的执行生成一个ActionResult，【View的呈现】的功能就是：通过InvokeActionResult方法对【Action的执行】中生成的ActionResult进行处理。（ActionResult泛指那些继承自抽象类System.Web.Mvc.ActonResult的类的实例）

　　为了会纵观【View的呈现】在全局中的位置，下面我们再来回顾下处理请求的整个流程：在此系列开篇的时候介绍了MVC的生命周期 ， 对于ASP.NET和ASP.NET MVC，都是将相应的类的方法注册到HttpApplication事件中，通过事件的依次执行从而完成对请求的处理。而针对MVC，请求是先 经过路由系统，然后由一个MvcHandler来处理的，当请求到来时，执行此MvcHandler的ProcessRequest方法（因为已将 MvcHandler类的ProcessRequest方法注册到HttpApplication的事件中，所以事件的执行就触发了此方法），下图就是一个简要的执行过程！

public class ControllerActionInvoker : IActionInvoker
{
	protected virtual void InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
	{
		actionResult.ExecuteResult(controllerContext);
	}
}

　　整个过程大致经过【Controller的激活】-->【Action的执行】-->【View的呈现】，由上图可知，【View的呈现】是由ControllerActionInvoker类中的InvokeActionResult方法来触发的！

 二、ActionResult的创建

 　　概述中提到，【View的呈现】的功能就是：通过InvokeActionResult方法对【Action的执行】中生成的ActionResult进行处理。即：ActionResult是在【Action的执行】中创建的，创建方式有：

• 请求没有通过Action的过滤器时，在过滤器的方法中创建一个ActionResult，将其当作最终的ActionResult，进行View的呈现
• 请求通过所有过滤器，将Action方法返回的ActionResult当作最终的ActionResult，进行View的呈现。
  注：在Action方法中其实调用Controller类中的方法来进行创建ActionResult实例的，如：return Content("OK");等同于return new ContentResult(){ Content="OK"};

例、自定义个Action过滤器，当没有通过时按照过滤器中定义的ActionResult进行View的呈现，具体执行过程下一部分介绍！

public class MyActionFilter:FilterAttribute,IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext filterContext)
    { 
    }

    public void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (filterContext.RouteData.DataTokens["OOK"] != "WuPeiqi")
        {
            ContentResult contentResult = new ContentResult();
            contentResult.Content = "DataToKens值有误";
            filterContext.Result = contentResult;
        }
    }
}
//将此过滤器应用的Action上，那么当请求中DataTokens的值不是不是相应的值时，就会用过滤器中的ContentResult对象来进行View的呈现，否则，就是利用Action方法Index中创建的ActionResult进行View的呈现！
public class HomeController : Controller
{
    [MyActionFilter]
    public ActionResult Index()
    {
        return Content("正确");
    }
}

三、View呈现过程分析

　　ASP.NET MVC的【View的呈现】其实就是执行ActonResult的ExcuteResult方法！而接下来我们介绍的就是这个ExcuteResult方法触发了那些操作！！！在介绍之前我们先来看看微软提供了那些ActionResult！（ActionResult泛指那些继承自System.Web.Mvc.ActionResult的类）

public abstract class ActionResult
{
    public abstract void ExecuteResult(ControllerContext context);
}

• EmptyResult
• ContentResult
• FileResult
• JavaScriptResult
• JsonResult
• HttpStatusCodeResult
• RedirectResult
• RedirectToRouteResult
• ViewResult

　　在ASP.NET MVC 的【Action的执行】中创建以上任意一个ActionResult对象，并执行该对象的ExcuteResult方法，从而进行【View的呈现】。这里的最后一项ViewResult比较特殊，它的处理流程相对复杂，涉及到Razor引擎什么的，之后详细介绍！

 下面就来看一些以上ActionResult的源码，了解下【View的呈现】如何实现！

1、EmptyResult

public class EmptyResult : ActionResult
{
	private static readonly EmptyResult _singleton = new EmptyResult();

	internal static EmptyResult Instance
	{
		get { return _singleton; }
	}

	public override void ExecuteResult(ControllerContext context)
	{
	}
}

　　由EmptyResult源码可见，其ExecuteReuslt方法什么都没做，也就是该ActionReuslt的【View的呈现】部分不做任何操作，那么此流程也就执行完毕。再看概述中的图可知，接下来进行【对TempData再一次处理】-->【释放Controller对象】，之后再继续HttpApplication其他的事件，包括对Session的处理、缓存的处理、对请求的返回等。

 2、ContentResult

　　ContentResult用于将字符串响应给客户端！

public class ContentResult : ActionResult
{
	public string Content { get; set; }

	public Encoding ContentEncoding { get; set; }

	public string ContentType { get; set; }

	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}

		HttpResponseBase response = context.HttpContext.Response;

		if (!String.IsNullOrEmpty(ContentType))
		{
			response.ContentType = ContentType;
		}
		if (ContentEncoding != null)
		{
			response.ContentEncoding = ContentEncoding;
		}
		if (Content != null)
		{
			response.Write(Content);
		}
	}
}

　　上述context.HttpContext.Response得到的是一个HttpResponseWrapper类型的对象response，该对象内有一个HttpResponse类型的私有变量_httpResponse，对于该HttpResponseWrapper对象的属性和方法其实都是执行私有变量_httpResponse对应的属性和方法！
　　由于HttpResponseWrapper对象属性和方法都是对私有变量_httpResponse的相关操作，而查看HttpResponseWrapper类部分源代码，_httpResponse变量是通过构造函数赋值的，而该构造函数的参数值是怎么来的呢？是在HttpApplication事件之前，通过HttpRuntime类创建请求上下文HttpContext对象时，又触发创建了HttpResponse对象并赋值到请求上下文HttpContext对象的一个私有变量中保存着的！
　　又由于HttpResponse对象的属性和方法又都是对私有变量_writer的相关操作，再看HttpResponse类的源代码，它的Write的方法其实是执行其TextWriter类型的私有变量_writer的Write方法，而该私有变量_writer是怎么来的呢？是在HttpApplication事件之前，通过HttpRuntime类创建请求上下文HttpContext对象时，触发创建了HttpResponse对象，之后又初始化HttpResponse对象的_writer字段为一个HttpWriter对象。
　　最终，执行HttpWriter对象的Write方法，根据ContentType定义的媒体类型和ContentEncoding定义的编码方法将字符串发送到 HTTP 输出流。ContentType定义的是MIME类型（默认为”text/html"），ContentEncoding定义的编码方式（默认是操作系统的当前 ANSI 代码页的编码System.Text.Encoding.Default）。

public class HttpResponseWrapper : HttpResponseBase
{
    private HttpResponse _httpResponse;
    //设置或获取响应内容的编码类型
    public override Encoding ContentEncoding
    {
        get
        {
            return this._httpResponse.ContentEncoding;
        }
        set
        {
            this._httpResponse.ContentEncoding = value;
        }
    } 
    
    public override string ContentType
    {
        get
        {
            return this._httpResponse.ContentType;
        }
        set
        {
            this._httpResponse.ContentType = value;
        }
    }
    public override void Write(string s)
    {
        this._httpResponse.Write(s);
    }
}

public sealed class HttpResponse
{
    private TextWriter _writer;
    private Encoding _encoding;
    private string _contentType = "text/html";
    
    public Encoding ContentEncoding
    {
        get
        {    
            if (this._encoding == null)
            {
                //获取webconfig文件中，globalization节点的值
                GlobalizationSection globalization = RuntimeConfig.GetLKGConfig(this._context).Globalization;
                if (globalization != null)
                {    
                    //设置Http响应的内容编码
                    this._encoding = globalization.ResponseEncoding;
                }
                //没有在globalization节点中配置编码类型
                if (this._encoding == null)
                {    
                    //获取操作系统的当前 ANSI 代码页的编码并赋值给Http响应内容的编码
                    this._encoding = Encoding.Default;
                }
            }
            return this._encoding;
        }
        set
        {
            if (value == null)
            {
                throw new ArgumentNullException("value");
            }
            //当没有设置编码类型或者编码类型和原来的不相同时，根据value重新设定编码类型
            if (this._encoding == null || !this._encoding.Equals(value))
            {
                this._encoding = value;
                this._encoder = null;
                if (this._httpWriter != null)
                {
                    //将HttpResponse类中与编码相关的属性值赋值到HttpWriter对象中与编码相关的属性
                    //以便HttpWriter输出响应流时按照此编码进行
                    this._httpWriter.UpdateResponseEncoding();
                }
            }
        }
    }
    
    public string ContentType
    {
        get
        {
            return this._contentType;
        }
        set
        {
            if (!this._headersWritten)
            {
                this._contentTypeSetByManagedCaller = true;
                this._contentType = value;
                return;
            }
            if (this._contentType == value)
            {
                return;
            }
            throw new HttpException(SR.GetString("Cannot_set_content_type_after_headers_sent"));
        }
    }    
    
    public void Write(string s)
    {
        this._writer.Write(s);
    }
}    

public sealed class HttpWriter : TextWriter
{
    //根据编码规则将字符串发送到 HTTP 输出流
    public override void Write(string s)
    {
        if (this._ignoringFurtherWrites)
        {
            return;
        }
        if (s == null)
        {
            return;
        }
        if (s.Length != 0)
        {
            if (s.Length < this._charBufferFree)
            {
                StringUtil.UnsafeStringCopy(s, 0, this._charBuffer, this._charBufferLength - this._charBufferFree, s.Length);
                this._charBufferFree -= s.Length;
            }
            else
            {
                int i = s.Length;
                int num = 0;
                while (i > 0)
                {
                    if (this._charBufferFree == 0)
                    {
                        this.FlushCharBuffer(false);
                    }
                    int num2 = (i < this._charBufferFree) ? i : this._charBufferFree;
                    StringUtil.UnsafeStringCopy(s, num, this._charBuffer, this._charBufferLength - this._charBufferFree, num2);
                    this._charBufferFree -= num2;
                    num += num2;
                    i -= num2;
                }
            }
        }
        if (!this._responseBufferingOn)
        {
            //将信息写入 HTTP 响应输出流。
            this._response.Flush();
        }
    }
    //更新编码相关的字段
    internal void UpdateResponseEncoding()
    {
        if (this._responseEncodingUpdated && this._charBufferLength != this._charBufferFree)
        {
            this.FlushCharBuffer(true);
        }
        this._responseEncoding = this._response.ContentEncoding;
        this._responseEncoder = this._response.ContentEncoder;
        this._responseCodePage = this._responseEncoding.CodePage;
        this._responseCodePageIsAsciiCompat = CodePageUtils.IsAsciiCompatibleCodePage(this._responseCodePage);
        this._responseEncodingUpdated = true;
    }    
    
}    

在ASP.NET MVC 的Controller类中提供了以下三个创建ContentResult的重载，当然也可以直接在Action中创建ContentReuslt对象并作为方法的返回值。

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IAsyncManagerContainer
{
    //省略其他方法
    protected internal ContentResult Content(string content)
    {
        return Content(content, null /* contentType */);
    }

    protected internal ContentResult Content(string content, string contentType)
    {
        return Content(content, contentType, null /* contentEncoding */);
    }

    protected internal virtual ContentResult Content(string content, string contentType, Encoding contentEncoding)
    {
        return new ContentResult
        {
            Content = content,
            ContentType = contentType,
            ContentEncoding = contentEncoding
        };
    }
}

扩展：请求上下文HttpContext、HttpResponse、HttpRequest创建流程
　　当请求到达IIS，IIS根据请求的后缀名判断是否加载aspnet_isapi.dll，一旦工作进程加载了aspnet_isapi.dll，就会加载IsapiRuntime，被加载的IsapiRuntime会接管Http请求，之后IsapiRuntime执行其方法ProcessRequest(IntPtr ecb, int iWRType)，该方法实现从ISAPI扩展控制块(ECB)中获取当前Http请求相关信息并封装到IsapiWorkrRequest对象中。然后将该对象传递给HttpRuntime，通过该类中的ProcessRequestInternal()方法创建HttpContext类实例，进入ProcessRequestInternal方法之后，内部触发一系列的方法，最终创建一个HttpContent实例（可通过HttpContent.Current获取到这个实例），且该实例会在整个生命周期内存活。创建HttpContext对象时，同时也创建了HttpRequest和HttpResponse对象，并赋值到私有字段中，通过公有属性去获取这两个对象。

　　之后HttpRuntime类会向HttpApplicationFactory类 提出请求，要求返回一个HttpApplication对象，HttpApplicationFactory在收到请求之后会检查是否有已经存在并且空闲的对象，如果有就取出一个HttpApplication对象返回给HttpRuntime类，如果没有，则要创建一个给HttpRuntime。

public sealed class ISAPIRuntime : MarshalByRefObject, IISAPIRuntime, IISAPIRuntime2, IRegisteredObject
{
    public ISAPIRuntime()
    {
        //将该ISAPIRuntime对象放在应用程序的已注册对象列表中
        HostingEnvironment.RegisterObject(this);
    }

    public int ProcessRequest(IntPtr ecb, int iWRType)
    {
        IntPtr intPtr = IntPtr.Zero;
        if (iWRType == 2)
        {
            intPtr = ecb;
            ecb = UnsafeNativeMethods.GetEcb(intPtr);
        }
        ISAPIWorkerRequest iSAPIWorkerRequest = null;
        int result;
        try
        {
            bool useOOP = iWRType == 1;
            //将ISAPI扩展控制块(ECB)中Http请求相关的信息封装到IsapiWorkerRequest对象中
            iSAPIWorkerRequest = ISAPIWorkerRequest.CreateWorkerRequest(ecb, useOOP);
            iSAPIWorkerRequest.Initialize();
            string appPathTranslated = iSAPIWorkerRequest.GetAppPathTranslated();
            string appDomainAppPathInternal = HttpRuntime.AppDomainAppPathInternal;
            if (appDomainAppPathInternal == null || StringUtil.EqualsIgnoreCase(appPathTranslated, appDomainAppPathInternal))
            {    
                //ASP.NET运行时开始执行
                HttpRuntime.ProcessRequestNoDemand(iSAPIWorkerRequest);
                result = 0;
            }
            else
            {
                HttpRuntime.ShutdownAppDomain(ApplicationShutdownReason.PhysicalApplicationPathChanged, SR.GetString("Hosting_Phys_Path_Changed", new object[]
                {
                    appDomainAppPathInternal,
                    appPathTranslated
                }));
                result = 1;
            }
        }
        //省略部分代码
        return result;
    }
}

public sealed class HttpRuntime
{
    //静态字段
    private static HttpRuntime _theRuntime;
    public HttpRuntime()
    {
    }
    //静态构造函数
    static HttpRuntime()
    {
        HttpRuntime.s_autogenKeys = new byte[1024];
        HttpRuntime.DirectorySeparatorString = new string(Path.DirectorySeparatorChar, 1);
        HttpRuntime.DoubleDirectorySeparatorString = new string(Path.DirectorySeparatorChar, 2);
        HttpRuntime.s_InvalidPhysicalPathChars = new char[]
        {
            '/',
            '?',
            '*',
            '<',
            '>',
            '|',
            '"'
        };
        HttpRuntime.s_initialized = false;
        HttpRuntime.s_isEngineLoaded = false;
        HttpRuntime.s_factoryLock = new object();
        HttpRuntime.AddAppDomainTraceMessage("*HttpRuntime::cctor");
        HttpRuntime.StaticInit();
        HttpRuntime._theRuntime = new HttpRuntime();
        HttpRuntime._theRuntime.Init();
        HttpRuntime.AddAppDomainTraceMessage("HttpRuntime::cctor*");
    }

    internal static void ProcessRequestNoDemand(HttpWorkerRequest wr)
    {
        RequestQueue requestQueue = HttpRuntime._theRuntime._requestQueue;
        wr.UpdateInitialCounters();
        if (requestQueue != null)
        {
            wr = requestQueue.GetRequestToExecute(wr);
        }
        if (wr != null)
        {
            HttpRuntime.CalculateWaitTimeAndUpdatePerfCounter(wr);
            wr.ResetStartTime();
            //继续执行
            HttpRuntime.ProcessRequestNow(wr);
        }
    }
    internal static void ProcessRequestNow(HttpWorkerRequest wr)
    {
        //继续执行
        HttpRuntime._theRuntime.ProcessRequestInternal(wr);
    }

    private void ProcessRequestInternal(HttpWorkerRequest wr)
    {
        Interlocked.Increment(ref this._activeRequestCount);
        if (this._disposingHttpRuntime)
        {
            try
            {
                wr.SendStatus(503, "Server Too Busy");
                wr.SendKnownResponseHeader(12, "text/html; charset=utf-8");
                byte[] bytes = Encoding.ASCII.GetBytes("<html><body>Server Too Busy</body></html>");
                wr.SendResponseFromMemory(bytes, bytes.Length);
                wr.FlushResponse(true);
                wr.EndOfRequest();
            }
            finally
            {
                Interlocked.Decrement(ref this._activeRequestCount);
            }
            return;
        }
        HttpContext httpContext;
        try
        {
            //创建请求上下文，继续执行
            httpContext = new HttpContext(wr, false);
        }
        catch
        {
            try
            {
                wr.SendStatus(400, "Bad Request");
                wr.SendKnownResponseHeader(12, "text/html; charset=utf-8");
                byte[] bytes2 = Encoding.ASCII.GetBytes("<html><body>Bad Request</body></html>");
                wr.SendResponseFromMemory(bytes2, bytes2.Length);
                wr.FlushResponse(true);
                wr.EndOfRequest();
                return;
            }
            finally
            {
                Interlocked.Decrement(ref this._activeRequestCount);
            }
        }
        wr.SetEndOfSendNotification(this._asyncEndOfSendCallback, httpContext);
        HostingEnvironment.IncrementBusyCount();
        try
        {
            try
            {
                this.EnsureFirstRequestInit(httpContext);
            }
            catch
            {
                if (!httpContext.Request.IsDebuggingRequest)
                {
                    throw;
                }
            }
            //初始化HttpResponse的TextWriter
            httpContext.Response.InitResponseWriter();
            //通过 HttpApplicationFactory获取HttpApplication实例
            IHttpHandler applicationInstance = HttpApplicationFactory.GetApplicationInstance(httpContext);
            if (applicationInstance == null)
            {
                throw new HttpException(SR.GetString("Unable_create_app_object"));
            }
            if (EtwTrace.IsTraceEnabled(5, 1))
            {
                EtwTrace.Trace(EtwTraceType.ETW_TYPE_START_HANDLER, httpContext.WorkerRequest, applicationInstance.GetType().FullName, "Start");
            }
            if (applicationInstance is IHttpAsyncHandler)
            {
                IHttpAsyncHandler httpAsyncHandler = (IHttpAsyncHandler)applicationInstance;
                httpContext.AsyncAppHandler = httpAsyncHandler;
                httpAsyncHandler.BeginProcessRequest(httpContext, this._handlerCompletionCallback, httpContext);
            }
            else
            {
                applicationInstance.ProcessRequest(httpContext);
                this.FinishRequest(httpContext.WorkerRequest, httpContext, null);
            }
        }
        catch (Exception e)
        {
            httpContext.Response.InitResponseWriter();
            this.FinishRequest(wr, httpContext, e);
        }
    }

}

public sealed class HttpContext : IServiceProvider, IPrincipalContainer
{
    //构造函数
    public HttpContext(HttpWorkerRequest wr)
    {
        this._wr = wr;
        //初始化HttpContext并创建HttpRequest和HttpResponse
        this.Init(new HttpRequest(wr, this), new HttpResponse(wr, this));
        //初始化HttpResponse的TextWriter
        this._response.InitResponseWriter();
    }
    private void Init(HttpRequest request, HttpResponse response)
    {
        this._request = request;
        this._response = response;
        //省略其他代码
    }
}

 3、FileResult

　　FileResult用于将某个物理文件的内容响应给客户端！

public abstract class FileResult : ActionResult
{
    private string _fileDownloadName;

    protected FileResult(string contentType)
    {
        if (String.IsNullOrEmpty(contentType))
        {
            throw new ArgumentException(MvcResources.Common_NullOrEmpty, "contentType");
        }

        ContentType = contentType;
    }

    public string ContentType { get; private set; }

    public string FileDownloadName
    {
        get { return _fileDownloadName ?? String.Empty; }
        set { _fileDownloadName = value; }
    }

    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }

        HttpResponseBase response = context.HttpContext.Response;
        //response.ContentType默认为“text/html”
        response.ContentType = ContentType;
        //如果没有指定文件被下载的名称，则按照内联的方法输出文件，否则按照附件的形式。
        if (!String.IsNullOrEmpty(FileDownloadName))
        {
            //处理文件名 并 构造“Content-Disposition”的报头的值
            //例如：文件名中包含Unicode码或包含特殊符号等
            string headerValue = ContentDispositionUtil.GetHeaderValue(FileDownloadName);
            //采用附件形式，需要为响应创建一个名称为“Content-Disposition”的报头，该报头的值格式为“attachment;filename={文件名}”
            context.HttpContext.Response.AddHeader("Content-Disposition", headerValue);
        }

        WriteFile(response);
    }

    protected abstract void WriteFile(HttpResponseBase response);
    
    //处理文件名并构造 “Content-Disposition”的报头的值
    internal static class ContentDispositionUtil
    {
        private const string HexDigits = "0123456789ABCDEF";

        private static void AddByteToStringBuilder(byte b, StringBuilder builder)
        {
            builder.Append('%');

            int i = b;
            AddHexDigitToStringBuilder(i >> 4, builder);
            AddHexDigitToStringBuilder(i % 16, builder);
        }

        private static void AddHexDigitToStringBuilder(int digit, StringBuilder builder)
        {
            builder.Append(HexDigits[digit]);
        }

        private static string CreateRfc2231HeaderValue(string filename)
        {
            StringBuilder builder = new StringBuilder("attachment; filename*=UTF-8''");

            byte[] filenameBytes = Encoding.UTF8.GetBytes(filename);
            foreach (byte b in filenameBytes)
            {
                if (IsByteValidHeaderValueCharacter(b))
                {
                    builder.Append((char)b);
                }
                else
                {
                    AddByteToStringBuilder(b, builder);
                }
            }

            return builder.ToString();
        }

        public static string GetHeaderValue(string fileName)
        {
            // If fileName contains any Unicode characters, encode according
            // to RFC 2231 (with clarifications from RFC 5987)
            foreach (char c in fileName)
            {
                if ((int)c > 127)
                {
                    return CreateRfc2231HeaderValue(fileName);
                }
            }

            // Knowing there are no Unicode characters in this fileName, rely on
            // ContentDisposition.ToString() to encode properly.
            // In .Net 4.0, ContentDisposition.ToString() throws FormatException if
            // the file name contains Unicode characters.
            // In .Net 4.5, ContentDisposition.ToString() no longer throws FormatException
            // if it contains Unicode, and it will not encode Unicode as we require here.
            // The Unicode test above is identical to the 4.0 FormatException test,
            // allowing this helper to give the same results in 4.0 and 4.5.         
            ContentDisposition disposition = new ContentDisposition() { FileName = fileName };
            return disposition.ToString();
        }

        // Application of RFC 2231 Encoding to Hypertext Transfer Protocol (HTTP) Header Fields, sec. 3.2
        // http://greenbytes.de/tech/webdav/draft-reschke-rfc2231-in-http-latest.html
        private static bool IsByteValidHeaderValueCharacter(byte b)
        {
            if ((byte)'0' <= b && b <= (byte)'9')
            {
                return true; // is digit
            }
            if ((byte)'a' <= b && b <= (byte)'z')
            {
                return true; // lowercase letter
            }
            if ((byte)'A' <= b && b <= (byte)'Z')
            {
                return true; // uppercase letter
            }

            switch (b)
            {
                case (byte)'-':
                case (byte)'.':
                case (byte)'_':
                case (byte)'~':
                case (byte)':':
                case (byte)'!':
                case (byte)'$':
                case (byte)'&':
                case (byte)'+':
                    return true;
            }

            return false;
        }
    }
}

　　对于FileResult，具有一个表示媒体类型的只读属性ContentType，该属性在构造函数中被初始化。当我们基于某个物理文件创建相应的FileReuslt对象的时候应该根据文件的类型指定该媒体类型属性，例如：目标文件是.jpg图片，那么对应的媒体类型应该是“image/jpeg”；对于一个.pdf文件，则采用“application/pdf”。

　　对于FileResult，还具有一个表示下载文件名的属性FileDownloadName，如果该属性没有指定或者设置的值为null，则会按照内联的方式利用浏览器直接打开响应的文件，否则会以附件的形式被下载并且文件名为属性FileDownloadName的值。（查看FileResult源码可知，内联和附件的区别是响应是否包含“Content-Disposition”报头）
　　FileReult仅仅是一个抽象类，对于文件内容的输出实现在抽象方法WriteFile方法中。FileResult有三个派生类实现了WriterFile方法分别是：

public class FileContentResult : FileResult
{
    //参数为字节数组、响应的媒体类型
    public FileContentResult(byte[] fileContents, string contentType)
        : base(contentType)
    {
        if (fileContents == null)
        {
            throw new ArgumentNullException("fileContents");
        }

        FileContents = fileContents;
    }

    public byte[] FileContents { get; private set; }

    protected override void WriteFile(HttpResponseBase response)
    {
        //将字节数组输出
        response.OutputStream.Write(FileContents, 0, FileContents.Length);
    }
}

public class FileStreamResult : FileResult
{
    // default buffer size as defined in BufferedStream type
    private const int BufferSize = 0x1000;
    //参数为：文件流、媒体类型
    public FileStreamResult(Stream fileStream, string contentType)
        : base(contentType)
    {
        if (fileStream == null)
        {
            throw new ArgumentNullException("fileStream");
        }

        FileStream = fileStream;
    }

    public Stream FileStream { get; private set; }

    protected override void WriteFile(HttpResponseBase response)
    {
        // grab chunks of data and write to the output stream
        Stream outputStream = response.OutputStream;
        using (FileStream)
        {
            byte[] buffer = new byte[BufferSize];

            while (true)
            {
                int bytesRead = FileStream.Read(buffer, 0, BufferSize);
                if (bytesRead == 0)
                {
                    // no more data
                    break;
                }
                outputStream.Write(buffer, 0, bytesRead);
            }
        }
    }
}

public class FilePathResult : FileResult
{
    //参数为：文件路径、媒体类型
    public FilePathResult(string fileName, string contentType)
        : base(contentType)
    {
        if (String.IsNullOrEmpty(fileName))
        {
            throw new ArgumentException(MvcResources.Common_NullOrEmpty, "fileName");
        }

        FileName = fileName;
    }

    public string FileName { get; private set; }

    protected override void WriteFile(HttpResponseBase response)
    {
        response.TransmitFile(FileName);
    }
}

　　以上的三个继承自FileResult的类，最终都是通过 文件的字节数组 的形式发送到Http输出流，不同的是作为开发者其起始点不一，FileContentResult传入字节数组然后将内容写入当前Http响应的输出流，FileStreamReuslt传入数据流，之后内部存入字节数组再将内容写入当前Http响应的输出流，FilePathResult传入文件地址，之后内部读取文件并存入字节数组再将内容写入当前Http响应的输出流。

 在ASP.NET MVC 的Controller类中提供了创建以上三个FileResult派生类的对象的重载，当然也可以直接在Action中创建相应的FileReuslt对象并作为方法的返回值。

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IAsyncManagerContainer
{
    protected internal FileContentResult File(byte[] fileContents, string contentType)
    {
        return File(fileContents, contentType, null /* fileDownloadName */);
    }

    protected internal virtual FileContentResult File(byte[] fileContents, string contentType, string fileDownloadName)
    {
        return new FileContentResult(fileContents, contentType) { FileDownloadName = fileDownloadName };
    }

    protected internal FileStreamResult File(Stream fileStream, string contentType)
    {
        return File(fileStream, contentType, null /* fileDownloadName */);
    }

    protected internal virtual FileStreamResult File(Stream fileStream, string contentType, string fileDownloadName)
    {
        return new FileStreamResult(fileStream, contentType) { FileDownloadName = fileDownloadName };
    }

    protected internal FilePathResult File(string fileName, string contentType)
    {
        return File(fileName, contentType, null /* fileDownloadName */);
    }

    protected internal virtual FilePathResult File(string fileName, string contentType, string fileDownloadName)
    {
        return new FilePathResult(fileName, contentType) { FileDownloadName = fileDownloadName };
    }
}

 4、JavaScriptResult

　　在后台动态的以字符串形式传入一段JavaScript脚本，并作为请求的响应使得脚本在客户端被执行！

public class JavaScriptResult : ActionResult
{
	public string Script { get; set; }

	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}

		HttpResponseBase response = context.HttpContext.Response;
		//指定响应的媒体类型
		response.ContentType = "application/x-javascript";

		if (Script != null)
		{
			response.Write(Script);
		}
	}
}

　　通过JavaScriptResult源码可以看出，其输出方式和ContentResult相同，不同的只是在JavaScriptResult中内部指定了输出的媒体类型为“application/x-javascript”（也可以是“text/javascript”），而我们也可以通过设置ContentResult的输出媒体类型来实现与JavaScriptResult相同的功能！

　　在ASP.NET MVC 的Controller类中提供了创建JavaScriptResult对象的方法，当然也可以直接在Action中创建JavaScriptResult对象并作为方法的返回值。

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IAsyncManagerContainer
{
    //省略其他代码
    protected internal virtual JavaScriptResult JavaScript(string script)
    {
        return new JavaScriptResult { Script = script };
    }
}

5、JsonResult

　　JsonResutl用于以Json的格式返回响应的数据！

public class JsonResult : ActionResult
{
	public JsonResult()
	{
		//定义枚举类型，默认拒绝Get请求的响应
		JsonRequestBehavior = JsonRequestBehavior.DenyGet;
	}

	public Encoding ContentEncoding { get; set; }

	public string ContentType { get; set; }

	public object Data { get; set; }

	//是否决绝Http Get请求（默认拒绝---构造函数中定义）
	public JsonRequestBehavior JsonRequestBehavior { get; set; }

	/// <summary>
	///指定 JSON 字符串的最大长度（UTF-8 字符的最大数量）。 默认长度为 102400。
	/// </summary>
	public int? MaxJsonLength { get; set; }

	/// <summary>
	/// 指定要序列化类型的最大深度。 默认的递归限制为 100。
	/// </summary>
	public int? RecursionLimit { get; set; }

	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}
		//如果拒绝Get请求&&发送来的请求也是Get方式
		if (JsonRequestBehavior == JsonRequestBehavior.DenyGet &&
			String.Equals(context.HttpContext.Request.HttpMethod, "GET", StringComparison.OrdinalIgnoreCase))
		{
			throw new InvalidOperationException(MvcResources.JsonRequest_GetNotAllowed);
		}

		HttpResponseBase response = context.HttpContext.Response;

		//默认媒体类型为"application/json"
		if (!String.IsNullOrEmpty(ContentType))
		{
			response.ContentType = ContentType;
		}
		else
		{
			response.ContentType = "application/json";
		}
		//编码类型的选取还是和ContentResult中一样，优先级：显示设定>WebConfig中节点>Encoding.Default
		if (ContentEncoding != null)
		{
			response.ContentEncoding = ContentEncoding;
		}
		if (Data != null)
		{
			//通过JavaScriptSerializer来将CLR对象序列化成Json格式字符串
			JavaScriptSerializer serializer = new JavaScriptSerializer();
			if (MaxJsonLength.HasValue)
			{
				//serializer.MaxJsonLength是JSON 字符串的最大长度（UTF-8 字符的最大数量）。 默认长度为 102400
				serializer.MaxJsonLength = MaxJsonLength.Value;
			}
			if (RecursionLimit.HasValue)
			{
				//serializer.RecursionLimit是指要序列化类型的最大深度。 默认的递归限制为 100
				serializer.RecursionLimit = RecursionLimit.Value;
			}
			//将Json格式的字符串写入当前Http响应的输出流
			response.Write(serializer.Serialize(Data));
		}
	}
}

public enum JsonRequestBehavior
{
	AllowGet,
	DenyGet,
}

　　对于JsonResult，其构造函数中为属性JsonRequestBehavior设置了一个枚举值DenyGet，该枚举值的作用就是拒绝对GET请求进行响应，也就是默认情况下，对于Json格式的数据响应，Get请求是不予支持的。如果想要支持Get请求，可以显示的设置JsonRequestBehavior属性的枚举值为AllowGet。
　　对于JsonResult，其默认的媒体类型为“application/json”。
　　JsonResult就是将CLR对象到Json格式字符串的序列化过程，而上述源码中的object类型的Data属性就是用来获取或设置原始的CLR对象，原始的CLR对象通过JavaScriptSerializer类的Serialize方法的序列化，将CLR对象转换成Json格式的字符串。在JavaScriptSerializer类在对CLR对象进行序列化时还可以对过程进行一些设置，即：MaxJsonLength（Json字符串的最大长度）、RecursionLimit（序列化类时递归的最大深度）。可以在JsonResult对应的属性中设置，也可以在WebConfig中设置。更多设置

<configuration>
  <system.web.extensions>
    <scripting>
      <webServices>
        <jsonSerialization maxJsonLength="5000"/>
      </webServices>
    </scripting>
  </system.web.extensions>
</configuration>

　　在ASP.NET MVC 的Controller类中提供了一下创建JsonResult对象的方法，当然也可以直接在Action中创建JsonResult对象并作为方法的返回值。

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IAsyncManagerContainer
{
    //省略其他代码
    protected internal JsonResult Json(object data)
    {
        return Json(data, null /* contentType */, null /* contentEncoding */, JsonRequestBehavior.DenyGet);
    }

    protected internal JsonResult Json(object data, string contentType)
    {
        return Json(data, contentType, null /* contentEncoding */, JsonRequestBehavior.DenyGet);
    }

    protected internal virtual JsonResult Json(object data, string contentType, Encoding contentEncoding)
    {
        return Json(data, contentType, contentEncoding, JsonRequestBehavior.DenyGet);
    }

    protected internal JsonResult Json(object data, JsonRequestBehavior behavior)
    {
        return Json(data, null /* contentType */, null /* contentEncoding */, behavior);
    }

    protected internal JsonResult Json(object data, string contentType, JsonRequestBehavior behavior)
    {
        return Json(data, contentType, null /* contentEncoding */, behavior);
    }

    protected internal virtual JsonResult Json(object data, string contentType, Encoding contentEncoding, JsonRequestBehavior behavior)
    {
        return new JsonResult
        {
            Data = data,
            ContentType = contentType,
            ContentEncoding = contentEncoding,
            JsonRequestBehavior = behavior
        };
    }
}

6、HttpStatusCodeResult

　　HttpStatusCodeResult用于返回对Http请求响应状态的代码和一个可选的状态描述！

public class HttpStatusCodeResult : ActionResult
{
	public HttpStatusCodeResult(int statusCode)
		: this(statusCode, null)
	{
	}
	//HttStatusCode是个枚举类型，用于定义状态代码
	public HttpStatusCodeResult(HttpStatusCode statusCode)
		: this(statusCode, null)
	{
	}

	public HttpStatusCodeResult(HttpStatusCode statusCode, string statusDescription)
		: this((int)statusCode, statusDescription)
	{
	}

	public HttpStatusCodeResult(int statusCode, string statusDescription)
	{
		StatusCode = statusCode;
		StatusDescription = statusDescription;
	}
	//响应状态代码
	public int StatusCode { get; private set; }
	//响应状态描述
	public string StatusDescription { get; private set; }

	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}
                //默认状态代码为：200
		context.HttpContext.Response.StatusCode = StatusCode;
		if (StatusDescription != null)
		{
			context.HttpContext.Response.StatusDescription = StatusDescription;
		}
	}
}

　　HttpStatusCodeResult为Http的响应头设置状态代码和状态描述，设置时，可以通过构造函数传入值也可以通过给属性赋值来操作。对于HttpStatustCodeResult的构造函数中HttpStatusCode类型的参数，它是一个枚举类型，其中包含了众多Http响应头状态。
　　值得一说的是，如果我们采用Visual StudioDvelopment Server作为Web应用的宿主，通过HttpStatusCodeResult的StatusDescription属性设置的状态描述信息不会反映在Http响应中，只有采用IIS作为宿主才会真正将此信息写入响应消息。

public enum HttpStatusCode
{
    Continue = 100,
    SwitchingProtocols,
    OK = 200,
    Created,
    Accepted,
    NonAuthoritativeInformation,
    NoContent,
    ResetContent,
    PartialContent,
    MultipleChoices = 300,
    Ambiguous = 300,
    MovedPermanently,
    Moved = 301,
    Found,
    Redirect = 302,
    SeeOther,
    RedirectMethod = 303,
    NotModified,
    UseProxy,
    Unused,
    TemporaryRedirect,
    RedirectKeepVerb = 307,
    BadRequest = 400,
    Unauthorized,
    PaymentRequired,
    Forbidden,
    NotFound,
    MethodNotAllowed,
    NotAcceptable,
    ProxyAuthenticationRequired,
    RequestTimeout,
    Conflict,
    Gone,
    LengthRequired,
    PreconditionFailed,
    RequestEntityTooLarge,
    RequestUriTooLong,
    UnsupportedMediaType,
    RequestedRangeNotSatisfiable,
    ExpectationFailed,
    UpgradeRequired = 426,
    InternalServerError = 500,
    NotImplemented,
    BadGateway,
    ServiceUnavailable,
    GatewayTimeout,
    HttpVersionNotSupported
}

　　ASP.NET MVC中有两个继承自HttpStatusCodeResult的类，即：HttpNotFoundResult和AuthorizeAttribute，用于指定特定相应状态和状态描述，本质上还是执行HttpStatusCodeResult来完成，只不过在内部为HttpStatuCodeResult指定了响应状态，分别是404、401。

public class HttpNotFoundResult : HttpStatusCodeResult
{
    public HttpNotFoundResult()
        : this(null)
    {
    }

    // NotFound is equivalent to HTTP status 404.
    public HttpNotFoundResult(string statusDescription)
        : base(HttpStatusCode.NotFound, statusDescription)
    {
    }
}

public class HttpUnauthorizedResult : HttpStatusCodeResult
{
    public HttpUnauthorizedResult()
        : this(null)
    {
    }

    // Unauthorized is equivalent to HTTP status 401, the status code for unauthorized
    // access. Other code might intercept this and perform some special logic. For
    // example, the FormsAuthenticationModule looks for 401 responses and instead
    // redirects the user to the login page.
    public HttpUnauthorizedResult(string statusDescription)
        : base(HttpStatusCode.Unauthorized, statusDescription)
    {
    }
}

7、RedirecteResult

　　RedirectResult用于实现针对某个地址的重定向！

public class RedirectResult : ActionResult
{
	public RedirectResult(string url)
		: this(url, permanent: false)
	{
	}

	public RedirectResult(string url, bool permanent)
	{
		if (String.IsNullOrEmpty(url))
		{
			throw new ArgumentException(MvcResources.Common_NullOrEmpty, "url");
		}

		Permanent = permanent;
		Url = url;
	}
	//是否永久重定向，默认为否。（永久重定向的Http状态码为301，否则是暂时重定向Http状态码为302）
	public bool Permanent { get; private set; }
	//要跳转的地址（相对地址或绝对地址）
	public string Url { get; private set; }

	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}
		if (context.IsChildAction)
		{
			throw new InvalidOperationException(MvcResources.RedirectAction_CannotRedirectInChildAction);
		}
		//处理Url地址，相对地址的处理。
		string destinationUrl = UrlHelper.GenerateContentUrl(Url, context.HttpContext);
		context.Controller.TempData.Keep();
		//是否永久重定向
		if (Permanent)
		{
			context.HttpContext.Response.RedirectPermanent(destinationUrl, endResponse: false);
		}
		else
		{
			context.HttpContext.Response.Redirect(destinationUrl, endResponse: false);
		}
	}
}

　　对于RedirectResult，可以定义暂时重定向（302重定向）和永久重定向（301重定向），两种重定向的不同作用主要体现在SEO上，搜索引擎会使用永久重定向目标地址更新自己的索引，而暂时重定向则不会。另外，永久重定向是在ASP.NET 4之后引进的，在之前如果想要实现永久重定向的话，需要自己来设置Http响应状态码为301。
　　对于UrlHelper.GenerateCotentUrl方法，用来处理Url。当定义的Url为相对地址时，如：~/xxx/xxx，该方法会利用请求上下文来补全地址。

public static string GenerateContentUrl(string contentPath, HttpContextBase httpContext)
{
	if (string.IsNullOrEmpty(contentPath))
	{
		throw new ArgumentException(MvcResources.Common_NullOrEmpty, "contentPath");
	}
	if (httpContext == null)
	{
		throw new ArgumentNullException("httpContext");
	}
	if (contentPath[0] == '~')
	{
		return PathHelpers.GenerateClientUrl(httpContext, contentPath);
	}
	return contentPath;
}

　　对于ASP.NET MVC的Controller类中定义了一下几个方法来创建RedirectResult，然也可以直接在Action中创建RedirectResult对象并作为方法的返回值。

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IAsyncManagerContainer
{
    //省略其他代码
    protected internal virtual RedirectResult Redirect(string url)
    {
        if (String.IsNullOrEmpty(url))
        {
            throw new ArgumentException(MvcResources.Common_NullOrEmpty, "url");
        }

        return new RedirectResult(url);
    }

    protected internal virtual RedirectResult RedirectPermanent(string url)
    {
        if (String.IsNullOrEmpty(url))
        {
            throw new ArgumentException(MvcResources.Common_NullOrEmpty, "url");
        }

        return new RedirectResult(url, permanent: true);
    }
｝

8、RedirectToRoutResult

　　RedirectToRouteResult用于将路由信息中的Controller和Action拼接成Url，再进行跳转！

public class RedirectToRouteResult : ActionResult
{
	private RouteCollection _routes;

	public RedirectToRouteResult(RouteValueDictionary routeValues)
		:
			this(null, routeValues)
	{
	}

	public RedirectToRouteResult(string routeName, RouteValueDictionary routeValues)
		: this(routeName, routeValues, permanent: false)
	{
	}

	public RedirectToRouteResult(string routeName, RouteValueDictionary routeValues, bool permanent)
	{
		Permanent = permanent;
		RouteName = routeName ?? String.Empty;
		RouteValues = routeValues ?? new RouteValueDictionary();
	}

	public bool Permanent { get; private set; }

	public string RouteName { get; private set; }

	public RouteValueDictionary RouteValues { get; private set; }

	internal RouteCollection Routes
	{
		get
		{
			if (_routes == null)
			{
				_routes = RouteTable.Routes;
			}
			return _routes;
		}
		set { _routes = value; }
	}

	public override void ExecuteResult(ControllerContext context)
	{
		if (context == null)
		{
			throw new ArgumentNullException("context");
		}
		if (context.IsChildAction)
		{
			throw new InvalidOperationException(MvcResources.RedirectAction_CannotRedirectInChildAction);
		}

		string destinationUrl = UrlHelper.GenerateUrl(RouteName, null /* actionName */, null /* controllerName */, RouteValues, Routes, context.RequestContext, false /* includeImplicitMvcValues */);
		if (String.IsNullOrEmpty(destinationUrl))
		{
			throw new InvalidOperationException(MvcResources.Common_NoRouteMatched);
		}

		context.Controller.TempData.Keep();

		if (Permanent)
		{
			context.HttpContext.Response.RedirectPermanent(destinationUrl, endResponse: false);
		}
		else
		{
			context.HttpContext.Response.Redirect(destinationUrl, endResponse: false);
		}
	}
}

　　RedirectToRouteResult和RedirectResult都是实现重定向，只不过RedirectToRouteResult的跳转地址是通过路由信息中的Controller和Action的拼接来完成的，其他均和RedirectResult相同！

　　ASP.NET MVC在Controller类中定义了几个方法用于创建RedirectToRouteResult对象，当然也可以直接在Action中创建RedirectToRouteResult对象并作为方法的返回值。

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IAsyncManagerContainer
{
    //省略其他代码
    protected internal RedirectToRouteResult RedirectToAction(string actionName)
    {
        return RedirectToAction(actionName, (RouteValueDictionary)null);
    }

    protected internal RedirectToRouteResult RedirectToAction(string actionName, object routeValues)
    {
        return RedirectToAction(actionName, new RouteValueDictionary(routeValues));
    }

    protected internal RedirectToRouteResult RedirectToAction(string actionName, RouteValueDictionary routeValues)
    {
        return RedirectToAction(actionName, null /* controllerName */, routeValues);
    }

    protected internal RedirectToRouteResult RedirectToAction(string actionName, string controllerName)
    {
        return RedirectToAction(actionName, controllerName, (RouteValueDictionary)null);
    }

    protected internal RedirectToRouteResult RedirectToAction(string actionName, string controllerName, object routeValues)
    {
        return RedirectToAction(actionName, controllerName, new RouteValueDictionary(routeValues));
    }

    protected internal virtual RedirectToRouteResult RedirectToAction(string actionName, string controllerName, RouteValueDictionary routeValues)
    {
        RouteValueDictionary mergedRouteValues;

        if (RouteData == null)
        {
            mergedRouteValues = RouteValuesHelpers.MergeRouteValues(actionName, controllerName, null, routeValues, includeImplicitMvcValues: true);
        }
        else
        {
            mergedRouteValues = RouteValuesHelpers.MergeRouteValues(actionName, controllerName, RouteData.Values, routeValues, includeImplicitMvcValues: true);
        }

        return new RedirectToRouteResult(mergedRouteValues);
    }

    protected internal RedirectToRouteResult RedirectToActionPermanent(string actionName)
    {
        return RedirectToActionPermanent(actionName, (RouteValueDictionary)null);
    }

    protected internal RedirectToRouteResult RedirectToActionPermanent(string actionName, object routeValues)
    {
        return RedirectToActionPermanent(actionName, new RouteValueDictionary(routeValues));
    }

    protected internal RedirectToRouteResult RedirectToActionPermanent(string actionName, RouteValueDictionary routeValues)
    {
        return RedirectToActionPermanent(actionName, null /* controllerName */, routeValues);
    }

    protected internal RedirectToRouteResult RedirectToActionPermanent(string actionName, string controllerName)
    {
        return RedirectToActionPermanent(actionName, controllerName, (RouteValueDictionary)null);
    }

    protected internal RedirectToRouteResult RedirectToActionPermanent(string actionName, string controllerName, object routeValues)
    {
        return RedirectToActionPermanent(actionName, controllerName, new RouteValueDictionary(routeValues));
    }

    protected internal virtual RedirectToRouteResult RedirectToActionPermanent(string actionName, string controllerName, RouteValueDictionary routeValues)
    {
        RouteValueDictionary implicitRouteValues = (RouteData != null) ? RouteData.Values : null;

        RouteValueDictionary mergedRouteValues =
            RouteValuesHelpers.MergeRouteValues(actionName, controllerName, implicitRouteValues, routeValues, includeImplicitMvcValues: true);

        return new RedirectToRouteResult(null, mergedRouteValues, permanent: true);
    }

    protected internal RedirectToRouteResult RedirectToRoute(object routeValues)
    {
        return RedirectToRoute(new RouteValueDictionary(routeValues));
    }

    protected internal RedirectToRouteResult RedirectToRoute(RouteValueDictionary routeValues)
    {
        return RedirectToRoute(null /* routeName */, routeValues);
    }

    protected internal RedirectToRouteResult RedirectToRoute(string routeName)
    {
        return RedirectToRoute(routeName, (RouteValueDictionary)null);
    }

    protected internal RedirectToRouteResult RedirectToRoute(string routeName, object routeValues)
    {
        return RedirectToRoute(routeName, new RouteValueDictionary(routeValues));
    }

    protected internal virtual RedirectToRouteResult RedirectToRoute(string routeName, RouteValueDictionary routeValues)
    {
        return new RedirectToRouteResult(routeName, RouteValuesHelpers.GetRouteValues(routeValues));
    }

    protected internal RedirectToRouteResult RedirectToRoutePermanent(object routeValues)
    {
        return RedirectToRoutePermanent(new RouteValueDictionary(routeValues));
    }

    protected internal RedirectToRouteResult RedirectToRoutePermanent(RouteValueDictionary routeValues)
    {
        return RedirectToRoutePermanent(null /* routeName */, routeValues);
    }

    protected internal RedirectToRouteResult RedirectToRoutePermanent(string routeName)
    {
        return RedirectToRoutePermanent(routeName, (RouteValueDictionary)null);
    }

    protected internal RedirectToRouteResult RedirectToRoutePermanent(string routeName, object routeValues)
    {
        return RedirectToRoutePermanent(routeName, new RouteValueDictionary(routeValues));
    }

    protected internal virtual RedirectToRouteResult RedirectToRoutePermanent(string routeName, RouteValueDictionary routeValues)
    {
        return new RedirectToRouteResult(routeName, RouteValuesHelpers.GetRouteValues(routeValues), permanent: true);
    }

｝

9、ViewResult

　　ViewResult内容包含了：PartialViewResult和ViewResult。ViewResult将视图页的内容响应给客户端，而PartialViewResult称分部视图，其响应请求时不输出那写html、head、body等标签，只是将分部视图中内容返回！由于ViewResult和PartialViewResult在进行【View呈现】的过程大致相同，所以此处就只针对ViewResult进行详细解读，而PartialViewRsult详细过程将不再敖述。（分部视图的更多信息：关于如何PartialViewResult的使用）

public abstract class ViewResultBase : ActionResult
{
    private DynamicViewDataDictionary _dynamicViewData;
    private TempDataDictionary _tempData;
    private ViewDataDictionary _viewData;
    private ViewEngineCollection _viewEngineCollection;
    private string _viewName;

    public object Model
    {
        get { return ViewData.Model; }
    }

    public TempDataDictionary TempData
    {
        get
        {
            if (_tempData == null)
            {
                _tempData = new TempDataDictionary();
            }
            return _tempData;
        }
        set { _tempData = value; }
    }

    public IView View { get; set; }

    public dynamic ViewBag
    {
        get
        {
            if (_dynamicViewData == null)
            {
                _dynamicViewData = new DynamicViewDataDictionary(() => ViewData);
            }
            return _dynamicViewData;
        }
    }
    public ViewDataDictionary ViewData
    {
        get
        {
            if (_viewData == null)
            {
                _viewData = new ViewDataDictionary();
            }
            return _viewData;
        }
        set { _viewData = value; }
    }

    //获取或设置视图引擎，ASP.NET有两个视图引擎，分别是：WebFormViewEngine、RazorViewEngine。
    public ViewEngineCollection ViewEngineCollection
    {
        get { return _viewEngineCollection ?? ViewEngines.Engines; }
        set { _viewEngineCollection = value; }
    }

    public string ViewName
    {
        get { return _viewName ?? String.Empty; }
        set { _viewName = value; }
    }

    public override void ExecuteResult(ControllerContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException("context");
        }
        //如果没有设置ViewName就将当前Action作为ViewName
        if (String.IsNullOrEmpty(ViewName))
        {
            ViewName = context.RouteData.GetRequiredString("action");
        }

        ViewEngineResult result = null;

        if (View == null)
        {
            //通过视图引擎去寻找视图
            result = FindView(context);
            View = result.View;
        }

        TextWriter writer = context.HttpContext.Response.Output;
        ViewContext viewContext = new ViewContext(context, View, ViewData, TempData, writer);
        //使用指定的编写器对象来呈现指定的视图上下文
        View.Render(viewContext, writer);

        if (result != null)
        {
            result.ViewEngine.ReleaseView(context, View);
        }
    }

    protected abstract ViewEngineResult FindView(ControllerContext context);
}

public class ViewResult : ViewResultBase
{
    private string _masterName;

    public string MasterName
    {
        get { return _masterName ?? String.Empty; }
        set { _masterName = value; }
    }

    protected override ViewEngineResult FindView(ControllerContext context)
    {
        //根据View引擎去寻找View
        //此处ViewEngineCollection是ViewResultBase类中的一个属性，表示视图引擎集合。
        ViewEngineResult result = ViewEngineCollection.FindView(context, ViewName, MasterName);
        //如果找到了指定的VIew，则返回。
        if (result.View != null)
        {
            return result;
        }
        //没有找到指定的View，那么就将查找路径给通过异常返回。
        StringBuilder locationsText = new StringBuilder();
        foreach (string location in result.SearchedLocations)
        {
            locationsText.AppendLine();
            locationsText.Append(location);
        }
        throw new InvalidOperationException(String.Format(CultureInfo.CurrentCulture,
                                                          MvcResources.Common_ViewNotFound, ViewName, locationsText));
    }
}

public class PartialViewResult : ViewResultBase
{
    /// <summary>Returns the <see cref="T:System.Web.Mvc.ViewEngineResult" /> object that is used to render the view.</summary>
    /// <returns>The view engine result.</returns>
    /// <param name="context">The controller context.</param>
    /// <exception cref="T:System.InvalidOperationException">An error occurred while the method was attempting to find the view.</exception>
    protected override ViewEngineResult FindView(ControllerContext context)
    {
        ViewEngineResult viewEngineResult = base.ViewEngineCollection.FindPartialView(context, base.ViewName);
        if (viewEngineResult.View != null)
        {
            return viewEngineResult;
        }
        StringBuilder stringBuilder = new StringBuilder();
        foreach (string current in viewEngineResult.SearchedLocations)
        {
            stringBuilder.AppendLine();
            stringBuilder.Append(current);
        }
        throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, MvcResources.Common_PartialViewNotFound, new object[]
        {
            base.ViewName,
            stringBuilder
        }));
    }
}

Controller类中定义的创建ViewResult和PartialViewResult对象的方法：

public abstract class Controller : ControllerBase, IActionFilter, IAuthorizationFilter, IDisposable, IExceptionFilter, IResultFilter, IAsyncController, IController, IAsyncManagerContainer
{
    //省略其他代码...
    
    //PartialViewResult
    protected internal PartialViewResult PartialView()
    {
        return this.PartialView(null, null);
    }
    protected internal PartialViewResult PartialView(object model)
    {
        return this.PartialView(null, model);
    }
    protected internal PartialViewResult PartialView(string viewName)
    {
        return this.PartialView(viewName, null);
    }
    protected internal virtual PartialViewResult PartialView(string viewName, object model)
    {
        if (model != null)
        {
            base.ViewData.Model = model;
        }
        return new PartialViewResult
        {
            ViewName = viewName,
            ViewData = base.ViewData,
            TempData = base.TempData,
            ViewEngineCollection = this.ViewEngineCollection
        };
    }
    //ViewResult
    protected internal ViewResult View()
    {
        string viewName = null;
        string masterName = null;
        object model = null;
        return this.View(viewName, masterName, model);
    }
    protected internal ViewResult View(object model)
    {
        return this.View(null, null, model);
    }
    protected internal ViewResult View(string viewName)
    {
        string masterName = null;
        object model = null;
        return this.View(viewName, masterName, model);
    }
    protected internal ViewResult View(string viewName, string masterName)
    {
        return this.View(viewName, masterName, null);
    }
    protected internal ViewResult View(string viewName, object model)
    {
        return this.View(viewName, null, model);
    }
    protected internal virtual ViewResult View(string viewName, string masterName, object model)
    {
        if (model != null)
        {
            base.ViewData.Model = model;
        }
        return new ViewResult
        {
            ViewName = viewName,
            MasterName = masterName,
            ViewData = base.ViewData,
            TempData = base.TempData,
            ViewEngineCollection = this.ViewEngineCollection
        };
    }
    protected internal ViewResult View(IView view)
    {
        return this.View(view, null);
    }
    protected internal virtual ViewResult View(IView view, object model)
    {
        if (model != null)
        {
            base.ViewData.Model = model;
        }
        return new ViewResult
        {
            View = view,
            ViewData = base.ViewData,
            TempData = base.TempData
        };
    }
}

ViewResult进行呈现的大致流程为：

• 获取视图引擎，默认有两个：ASPX引擎、Razor引擎。
• 根据视图页名称，通过视图引擎去检查是否存在对应的视图页，如果存在，则创建视图对象。如果不存在，则将所有视图引擎寻找过的路径作为异常返回。
• 创建视图对象之后，处理视图页中的内容（先处理_ViewStart.cshtml，之后再处理相应的试图页）。例如：TempData、Html.XXX等。
• 视图页内容处理完毕之后，就将视图内容作为响应返回给客户端。

　　对于上述流程中的第三步中，创建视图对象之后，通过它来对视图页进行处理。在对处理视图页时，首先要处理_ViewStart.cshtml文件（相当与asp.net中的Page_Load方法），之后再去处理请求的试图页。例如：如果在~/View/HomeController目录下创建一个_ViewStart.cshtml文件，那么之后当请求HomeController目录下的任意视图页时，都会先执行_ViewStart.cshtml，如果再在~/View目录下创建一个_ViewStart.cshtml的话，那么在请求HomeController目录下的任意视图页时，那么两个_ViewStart.cshtml都会先执行，且顺序为：先~/View目录下后~/View/HomeController目录下的_ViewStart.cshtml。

由于ViewResult的详细过程涉及内容较多，所以将另写一篇博文来对其进行详细分析：《白话学习MVC(十)View的呈现二》