Question

我实际上有以下代码：

private Stopwatch _sw;

public void DownloadFile(string url, string fileName)
{
    string path = @"C:\DL\";

    Thread bgThread = new Thread(() =>
    {

        _sw = new Stopwatch();
        _sw.Start();
        labelDownloadAudioStatusText.Visibility = Visibility.Visible;
        using (WebClient webClient = new WebClient())
        {
            webClient.DownloadFileCompleted +=
                new AsyncCompletedEventHandler(DownloadCompleted);
            webClient.DownloadProgressChanged +=
                new DownloadProgressChangedEventHandler(DownloadStatusChanged);
            webClient.DownloadFileAsync(new Uri(url), path + fileName);
        }
    });

    bgThread.Start();
}

void DownloadStatusChanged(object sender, DownloadProgressChangedEventArgs e)
{
    this.BeginInvoke((MethodInvoker) delegate
    {
        int percent = 0;
        if (e.ProgressPercentage != percent)
        {
            percent = e.ProgressPercentage;
            progressBarDownloadAudio.Value = percent;

            labelDownloadAudioProgress.Content = percent + "%";
            labelDownloadAudioDlRate.Content =
                (Convert.ToDouble(e.BytesReceived)/1024/
                _sw.Elapsed.TotalSeconds).ToString("0.00") + " kb/s";

            Thread.Sleep(50);
        }
    });
}

private void DownloadCompleted(object sender, AsyncCompletedEventArgs e)
{
    this.BeginInvoke((MethodInvoker) delegate
    {

        labelDownloadAudioDlRate.Content = "0 kb/s";
        labelDownloadAudioStatusText.Visibility = Visibility.Hidden;
    });
}

我的问题是，在没有外部线程的先前版本中，整个GUI偶尔冻结，并且在下载完成时GUI是流动的。所以我用Google搜索并找到了这个：https://stackoverflow.com/a/9459441/2288470

答案是将所有内容打包到一个单独的线程中，该线程执行与DownloadFileAsync的交互，但我得到了错误，找不到BeginInvoke方法。

Answer 1

使用WPF时，BeginInvoke类不会公开Window方法，就像WinForms中的Form一样。相反，您应该使用Dispatcher.BeginInvoke。

工作代码：

private Stopwatch _sw;

public void DownloadFile(string url, string fileName)
{
    string path = @"C:\DL\";

    Thread bgThread = new Thread(() =>
    {
        _sw = new Stopwatch();
        _sw.Start();
        labelDownloadAudioStatusText.Visibility = Visibility.Visible;
        using (WebClient webClient = new WebClient())
        {
            webClient.DownloadFileCompleted +=
                new AsyncCompletedEventHandler(DownloadCompleted);
            webClient.DownloadProgressChanged +=
                new DownloadProgressChangedEventHandler(DownloadStatusChanged);
            webClient.DownloadFileAsync(new Uri(url), path + fileName);
        }
    });

    bgThread.Start();
}

void DownloadStatusChanged(object sender, DownloadProgressChangedEventArgs e)
{
    Dispatcher.BeginInvoke((MethodInvoker) delegate
    {
        int percent = 0;

        if (e.ProgressPercentage != percent)
        {
            percent = e.ProgressPercentage;
            progressBarDownloadAudio.Value = percent;

            labelDownloadAudioProgress.Content = percent + "%";
            labelDownloadAudioDlRate.Content =
                (Convert.ToDouble(e.BytesReceived)/1024/
                _sw.Elapsed.TotalSeconds).ToString("0.00") + " kb/s";

            Thread.Sleep(50);
        }
    });
}

private void DownloadCompleted(object sender, AsyncCompletedEventArgs e)
{
    Dispatcher.BeginInvoke((MethodInvoker) delegate
    {
        labelDownloadAudioDlRate.Content = "0 kb/s";
        labelDownloadAudioStatusText.Visibility = Visibility.Hidden;
    });
}

Answer 2

Invoke方法和BeginInvoke方法在System.Windows.Forms.Control类上实现。如果您没有在Form Class中编写代码，则无法使用此方法。若要解决此问题，从System.Windows.Forms.Control类继承您的Job类，然后您可以使用BeginInvoke方法。请注意，您必须在主线程上创建实例。

public class JobClass : System.Windows.Forms.Control {
.....
}

通过WebClient / BeginInvoke方法创建多线程webdownload

2 个答案: