C#使用BeginInvoke和EndInvoke异步下载和获取返回结果

场景：为了防止UI卡死，使用异步下载文件

问题：采用多线程下载，关闭窗口后下载线程不能停止，线程操作麻烦。

参考：C#客户端的异步操作： http://www.cnblogs.com/fish-li/archive/2011/10/23/2222013.html

方案：采用BeginInvoke的方式调用下载方法，委托会自动启动新线程，停止时也不需要手动控制。使用EndInvoke获取返回结果。

try
{
    IAsyncResult ir = process.BeginInvoke(new HttpDownloadDelegate(HttpDownload),url,path); 
    bool result = process.EndInvoke(ir);
}
catch(Exception ex)
{
    MessageBox.Show(ex.Message);
}

//方法声明
public delegate bool HttpDownloadDelegate(string url, string path)

public bool HttpDownload(string url, string path)
{
    //下载方法...
}

HTTP下载：

/// <summary>
        /// http下载文件
        /// </summary>
        /// <param name="url">下载文件地址</param>
        /// <param name="path">文件存放地址，包含文件名</param>
        /// <returns></returns>
        public bool HttpDownload(string url, string path)
        {
            string tempPath = System.IO.Path.GetDirectoryName(path) + @"	emp";
            System.IO.Directory.CreateDirectory(tempPath);  //创建临时文件目录
            string tempFile = tempPath + @"" + System.IO.Path.GetFileName(path) + ".temp"; //临时文件
            if (System.IO.File.Exists(tempFile))
            {
                System.IO.File.Delete(tempFile);    //存在则删除
            }
            try
            {
                FileStream fs = new FileStream(tempFile, FileMode.Append, FileAccess.Write, FileShare.ReadWrite);
                // 设置参数
                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
                //发送请求并获取相应回应数据
                HttpWebResponse response = request.GetResponse() as HttpWebResponse;
                //直到request.GetResponse()程序才开始向目标网页发送Post请求
                Stream responseStream = response.GetResponseStream();
                //创建本地文件写入流
                //Stream stream = new FileStream(tempFile, FileMode.Create);
                byte[] bArr = new byte[1024];
                int size = responseStream.Read(bArr, 0, (int)bArr.Length);
                while (size > 0)
                {
                    //stream.Write(bArr, 0, size);
                    fs.Write(bArr, 0, size);
                    size = responseStream.Read(bArr, 0, (int)bArr.Length);
                }
                //stream.Close();
                fs.Close();
                responseStream.Close();
                System.IO.File.Move(tempFile, path);
                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }