Question

我正在制作一个WPF应用程序，我使用WebClient来下载文件。我想在ProgressPercentage控制器中显示ProgressBar。我在类中使用WebClient下载文件的方法。我的问题是如何将ProgressBar数据绑定到e.ProgressPercentage。

类中的方法（DownloadFile）：

public async Task DownloadProtocol(string address, string location)
{

        Uri Uri = new Uri(address);
        using (WebClient client = new WebClient())
        {
            //client.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
            //client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(DownloadProgress);
            client.DownloadProgressChanged += (o, e) =>
            {
                Console.WriteLine(e.BytesReceived + " " + e.ProgressPercentage);
                //ProgressBar = e.ProgressPercentage???
            };

            client.DownloadFileCompleted += (o, e) =>
            {
                if (e.Cancelled == true)
                {
                    Console.WriteLine("Download has been canceled.");
                }
                else
                {

                    Console.WriteLine("Download completed!");
                }

            };

            await client.DownloadFileTaskAsync(Uri, location);
        }

}

进度：

<ProgressBar HorizontalAlignment="Left" Height="24" Margin="130,127,0,0" VerticalAlignment="Top" Width="249"/>

Answer 1

要获得干净的解决方案，您需要一个ViewModel课程，我们会在其中创建StartDownload方法，您可以通过Command或button点击进行调用你的window。

另一方面，有一个很好的Type名为IProgress<T>。它对我们来说是一个 informer ，您可以像下面的示例一样玩它;）

在DownloadViewModel.cs中：

public sealed class DownloadViewModel : INotifyPropertyChanged
{
    private readonly IProgress<double> _progress;
    private double _progressValue;

    public double ProgressValue
    {
        get
        {
            return _progressValue;
        }
        set
        {
            _progressValue = value;
            OnPropertyChanged();
        }
    }

    public DownloadViewModel()
    {
        _progress = new Progress<double>(ProgressValueChanged);
    }

    private void ProgressValueChanged(double d)
    {
        ProgressValue = d;
    }

    public async void StartDownload(string address, string location)
    {
        await new MyDlClass().DownloadProtocol(_progress, address, location);
    }

    //-----------------------------------------------------------------------
    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

在MyDlClass中。 CS

public class MyDlClass { public async Task DownloadProtocol(IProgress<double> progress, string address, string location) { Uri Uri = new Uri(address); using (WebClient client = new WebClient()) { //client.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed); //client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(DownloadProgress); client.DownloadProgressChanged += (o, e) => { Console.WriteLine(e.BytesReceived + " " + e.ProgressPercentage); progress.Report(e.ProgressPercentage); }; client.DownloadFileCompleted += (o, e) => { if (e.Cancelled == true) { Console.WriteLine("Download has been canceled."); } else { Console.WriteLine("Download completed!"); } }; await client.DownloadFileTaskAsync(Uri, location); } } }

内MyWindow.Xaml.cs＆amp; MyWindow.Xaml

现在，您应该使用DataContext类的实例（通过Xaml或Code-Behind）填充您的窗口DownloadViewModel。

绑定到ProgressValue类的DownloadViewModel.cs属性：

<ProgressBar HorizontalAlignment="Left" Height="24" Margin="130,127,0,0" VerticalAlignment="Top" Width="249" Minimum="0" Maximum="100" Value="{Binding Path=ProgressValue}"/>

Finnaly，在你的按钮上点击OnClick：

if(this.DataContext!=null) ((DownloadViewModel)this.DataContext).StartDownload("__@Address__","__@Location__"); else MessageBox.Show("DataContext is Null!");

<强>结果：

Answer 2

您应该在方法中添加IProgress<double> progress参数，只要您的客户想要更新进度，然后调用progress.Report()。您的视图/窗口侧的IProgress将指向您将实施MyProgressBar.Value = value或其他任何内容的方法。

使用IProgress有效地删除了与提供更新的目标控件的交互，此外它还负责调用调度程序，因此您不会遇到通常无效的跨线程调用错误。

请参阅此帖子以获取示例：

http://blogs.msdn.com/b/dotnet/archive/2012/06/06/async-in-4-5-enabling-progress-and-cancellation-in-async-apis.aspx

WPF数据绑定ProgressBar

2 个答案: