如何自定义MVC控件？

今天公司要写学习总结，想着想着还是先写一篇关于MVC内部什么东东的博客整理整理再发表吧，一举两得。

之前写过了路由、过滤器等。今天就研究一下怎么自定义MVC控件吧。

本人技术小菜，不喜勿喷。。。。。（说这句话通常有两种情况，一种是牛人谦虚的说法，一种是怕受伤害提前准备个挡箭牌）

首先我们先去熟知一下MVC内部的那些控件是怎么实现的。

首先,Input标签是大佬，我给各位看管来上一小段Password的吧。

     
    public static class InputExtensions {
   public static MvcHtmlString Password(this HtmlHelper htmlHelper, string name) {
            return Password(htmlHelper, name, null /* value */);
        }

        public static MvcHtmlString Password(this HtmlHelper htmlHelper, string name, object value) {
            return Password(htmlHelper, name, value, null /* htmlAttributes */);
        }

        public static MvcHtmlString Password(this HtmlHelper htmlHelper, string name, object value, object htmlAttributes) {
            return Password(htmlHelper, name, value, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
        }

        public static MvcHtmlString Password(this HtmlHelper htmlHelper, string name, object value, IDictionary<string, object> htmlAttributes) {
            return PasswordHelper(htmlHelper, null /* metadata */, name, value, htmlAttributes);
        }

        [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]
        public static MvcHtmlString PasswordFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression) {
            return PasswordFor(htmlHelper, expression, null /* htmlAttributes */);
        }
}

这定义的都是扩展方法，实现了重载，我们看到最后一个方法调用的是PasswordHelper 方法

        private static MvcHtmlString PasswordHelper(HtmlHelper htmlHelper, ModelMetadata metadata, string name, object value, IDictionary<string, object> htmlAttributes) {
            return InputHelper(htmlHelper, InputType.Password, metadata, name, value, false /* useViewData */, false /* isChecked */, true /* setId */, true /* isExplicitValue */, htmlAttributes);
        }

但其最终调用的还是InputHelper方法，我们可以展开看看.....

        private static MvcHtmlString InputHelper(HtmlHelper htmlHelper, InputType inputType, ModelMetadata metadata, string name, object value, bool useViewData, bool isChecked, bool setId, bool isExplicitValue, IDictionary<string, object> htmlAttributes) {
            string fullName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
            if (String.IsNullOrEmpty(fullName)) {
                throw new ArgumentException(MvcResources.Common_NullOrEmpty, "name");
            }

            TagBuilder tagBuilder = new TagBuilder("input");
            tagBuilder.MergeAttributes(htmlAttributes);
            tagBuilder.MergeAttribute("type", HtmlHelper.GetInputTypeString(inputType));
            tagBuilder.MergeAttribute("name", fullName, true);

            string valueParameter = Convert.ToString(value, CultureInfo.CurrentCulture);
            bool usedModelState = false;

            switch (inputType) {
                case InputType.CheckBox:
                    bool? modelStateWasChecked = htmlHelper.GetModelStateValue(fullName, typeof(bool)) as bool?;
                    if (modelStateWasChecked.HasValue) {
                        isChecked = modelStateWasChecked.Value;
                        usedModelState = true;
                    }
                    goto case InputType.Radio;
                case InputType.Radio:
                    if (!usedModelState) {
                        string modelStateValue = htmlHelper.GetModelStateValue(fullName, typeof(string)) as string;
                        if (modelStateValue != null) {
                            isChecked = String.Equals(modelStateValue, valueParameter, StringComparison.Ordinal);
                            usedModelState = true;
                        }
                    }
                    if (!usedModelState && useViewData) {
                        isChecked = htmlHelper.EvalBoolean(fullName);
                    }
                    if (isChecked) {
                        tagBuilder.MergeAttribute("checked", "checked");
                    }
                    tagBuilder.MergeAttribute("value", valueParameter, isExplicitValue);
                    break;
                case InputType.Password:
                    if (value != null) {
                        tagBuilder.MergeAttribute("value", valueParameter, isExplicitValue);
                    }
                    break;
                default:
                    string attemptedValue = (string)htmlHelper.GetModelStateValue(fullName, typeof(string));
                    tagBuilder.MergeAttribute("value", attemptedValue ?? ((useViewData) ? htmlHelper.EvalString(fullName) : valueParameter), isExplicitValue);
                    break;
            }

            if (setId) {
                tagBuilder.GenerateId(fullName);
            }

            // If there are any errors for a named field, we add the css attribute.
            ModelState modelState;
            if (htmlHelper.ViewData.ModelState.TryGetValue(fullName, out modelState)) {
                if (modelState.Errors.Count > 0) {
                    tagBuilder.AddCssClass(HtmlHelper.ValidationInputCssClassName);
                }
            }

            tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata));

            if (inputType == InputType.CheckBox) {
                // Render an additional <input type="hidden".../> for checkboxes. This
                // addresses scenarios where unchecked checkboxes are not sent in the request.
                // Sending a hidden input makes it possible to know that the checkbox was present
                // on the page when the request was submitted.
                StringBuilder inputItemBuilder = new StringBuilder();
                inputItemBuilder.Append(tagBuilder.ToString(TagRenderMode.SelfClosing));

                TagBuilder hiddenInput = new TagBuilder("input");
                hiddenInput.MergeAttribute("type", HtmlHelper.GetInputTypeString(InputType.Hidden));
                hiddenInput.MergeAttribute("name", fullName);
                hiddenInput.MergeAttribute("value", "false");
                inputItemBuilder.Append(hiddenInput.ToString(TagRenderMode.SelfClosing));
                return MvcHtmlString.Create(inputItemBuilder.ToString());
            }

            return tagBuilder.ToMvcHtmlString(TagRenderMode.SelfClosing);
        }

该方法主要通过传递来的Input类型，还有一些name，value以及一些判断的界定来生产一个Input标签，最后返回一个MvcHtmlString对象。

其中实现我们就不做一一分析了，只是看看大概是如何实现的。

接下来我们自己定义一个简单的Input标签，类型为submit即提交的按钮。

namespace System.Web.Mvc.Html      
{
    public static class SubmitExtention
    {
        public const string DefaultSubmitValue = "提交";

        public static MvcHtmlString Submit(this HtmlHelper htmlHelper)
        {
            return Submit(htmlHelper);
        }

        public static MvcHtmlString Submit(this HtmlHelper htmlHelper, string value)
        {
            return Submit(htmlHelper, null, value);
        }

        public static MvcHtmlString Submit(this HtmlHelper htmlHelper, string name, string value)
        {
            return Submit(htmlHelper, name, value, null);
        }

        public static MvcHtmlString Submit(this HtmlHelper htmlHelper, string name, string value, IDictionary<string, string> attributes)
        {
            TagBuilder tag = new TagBuilder("input");
            tag.Attributes.Add("type", "submit");

            if (!string.IsNullOrEmpty(name))
            {
                tag.Attributes.Add("name", name);
            }

            if (!string.IsNullOrEmpty(value))
            {
                tag.Attributes.Add("value", value);
            }
            else
            {
                tag.Attributes.Add("value", DefaultSubmitValue);
            }

            if (null != attributes)
            {
                foreach (var attr in attributes)
                {
                    tag.Attributes.Add(attr.Key, attr.Value);
                }
            }
            return MvcHtmlString.Create(tag.ToString());
        }
    }
}

好了，我们去视图里看看吧。

点出来了吧，小伙伴们惊喜吗？

呵呵，其实一点都不惊喜，不久一个扩展方法吗？

不积跬步无以至千里，慢慢来，以后的路还很长，写博客只是为了总结，忘了的时候翻出来看看，温习温习，权当做笔记咯。

注意：

 在视图配置文件中没有添加引用的情况下，小伙伴们可能点不出。

如果不行，你们还是把命名空间改为System.Web.Mvc.Html，像我这样，不然是点不出来的。