c# - 带进度条的异步文件下载

Question

我正在尝试让进度条的进度随着 WebClient 下载进度的变化而变化。此代码仍在下载文件，但当我调用 startDownload() 时，窗口在下载文件时卡住。我希望用户能够在启动画面加载时看到进度变化。有什么方法可以解决此问题，以便用户可以看到 progressBar2 更改的进度吗？

private void startDownload()
{
    WebClient client = new WebClient();
    client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
    client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted);
    client.DownloadFileAsync(new Uri("http://joshua-ferrara.com/luahelper/lua.syn"), @"C:\LUAHelper\Syntax Files\lua.syn");
}
void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    double bytesIn = double.Parse(e.BytesReceived.ToString());
    double totalBytes = double.Parse(e.TotalBytesToReceive.ToString());
    double percentage = bytesIn / totalBytes * 100;
    label2.Text = "Downloaded " + e.BytesReceived + " of " + e.TotalBytesToReceive;
    progressBar1.Value = int.Parse(Math.Truncate(percentage).ToString());
}
void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    label2.Text = "Completed";
}

Answer 1

当您单击startDownload() 时，UI 线程将被卡住。如果您不想卡住表单，可以在另一个线程中使用 startDownload() 并在跨线程中进行进度更新。 一种方式，

private void startDownload()
{
    Thread thread = new Thread(() => {
          WebClient client = new WebClient();
          client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
          client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted);
          client.DownloadFileAsync(new Uri("http://joshua-ferrara.com/luahelper/lua.syn"), @"C:\LUAHelper\Syntax Files\lua.syn");
    });
    thread.Start();
}
void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    this.BeginInvoke((MethodInvoker) delegate {
        double bytesIn = double.Parse(e.BytesReceived.ToString());
        double totalBytes = double.Parse(e.TotalBytesToReceive.ToString());
        double percentage = bytesIn / totalBytes * 100;
        label2.Text = "Downloaded " + e.BytesReceived + " of " + e.TotalBytesToReceive;
        progressBar1.Value = int.Parse(Math.Truncate(percentage).ToString());
    });
}
void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    this.BeginInvoke((MethodInvoker) delegate {
         label2.Text = "Completed";
    }); 
}

像这样在谷歌阅读更多多线程 http://msdn.microsoft.com/en-us/library/ms951089.aspx

-修复了丢失的 close );到 bgThread 声明