C#backgroundWorker取消和调用

在进入代码之前,让我们先解决这个问题

1. 由于某些原因,在实际下载完成后,您有一个完全冗余的循环等待取消。因此 BtnStop
2. 当你打电话的时候 EditProcess.Text 从…起 Dnld cross-thread operation here . 在你的情况下,你应该通过 ReportProgress

现在你可以看到我

1. GoDownload 在移动 if (DnldBgWorker.CancellationPending) 检查下载循环。这应该使 StopBtn
2. 添加了 ProgressChanged ExecuteBtn_Click . 这是由 DnldBgWorker.ReportProgress 货物装载 方法这里我们将自定义格式的字符串传递为 UserState
3. ReportsProgress SupportsCancellation 属性,可能在designer属性框或代码lile中 DnldBgWorker.WorkerReportsProgress = true; DnldBgWorker.WorkerSupportsCancellation = true;

public partial class App : Form {
    //Some codes omitted
    public EditProcess Process = new EditProcess(ProcessTextBox);

    private void ExecuteBtn_Click (object sender, EventArgs e) {
        //DnldBgWorker is a backgroundWorker.
        Download Dnld = new Download(dir, Process);
        DnldBgWorker.DoWork += (obj, e) => GoDownload(Dnld, urllist, e);
        DnldBgWorker.RunWorkerAsync();
        DnldBgWorker.RunWorkerCompleted += (obj, e) => FinishExecution();
        DnldBgWorker.ProgressChanged += (s, e) => EditProcess.Text((string)e.UserState);;
    }

    private void GoDownload(Download Dnld, string[] urllist, EventArgs e) {
        foreach(string url in urllist) {
            Dnld.Dnld(url);
            DnldBgWorker.ReportProgress(0, String.Format($"Downloaded: {url}\r\n"));
            if (DnldBgWorker.CancellationPending) {
                e.Cancel = true;
                return;
            }
        }
    }

    private void StopBtn_Click(object sender, EventArgs e) {
        DnldBgWorker.CancelAsync();
    }
}

public class Download {
    // Some codes omitted
    public WebClient client = new WebClient();
    public EditProcess Process;

    public Download(string dir, EditProcess Process) {
        this.dir = dir;
        this.Process = Process;
    }

    public void Dnld() {
        client.DownloadFile(url, dir);
    }
}

public class EditProcess {
    public TextBox Box;

    public EditProcess(TextBox Box) {
        this.Box = Box;
    }

    public void Text(string textToAdd) {
        Box.Text += textToAdd;
    }
}

这里有两个问题:

关于取消-你需要在下载的循环中检查取消状态(因此只下载部分请求的文件),而不是在我不太理解的后一个循环中。

WebClient.DownloadFileAsync 和 WebClient.CancelAsync 联合体。

BackgroundWorker 通过将进度报告回UI线程 ReportProgress

至于如何取消线程。这是一个控制台应用程序的基本示例,我希望您可以将其放入更复杂的代码中。

void Main()
{
    var tokenSource = new CancellationTokenSource();
    System.Threading.Tasks.Task.Run(() => BackgroundThread(tokenSource.Token));

    Thread.Sleep(5000);
    tokenSource.Cancel();   
}

private void BackgroundThread(CancellationToken token)
{
    while (token.IsCancellationRequested == false) {
        Console.Write(".");
        Thread.Sleep(1000);
    }

    Console.WriteLine("\nCancellation Requested Thread Exiting...");
}

结果如下。

.....
Cancellation Requested Thread Exiting...

Updating Windows Form UI elements from another thread

要支持取消,您需要设置属性

 DnldBgWorker.WorkerSupportsCancellation = true;

不清楚您是否在其他地方设置了它,但您需要它来取消后台工作程序,因为您可以在MSDN上阅读

支持取消的后台工作人员。当此属性为true时, 您可以调用CancelAsync方法来中断后台

另外,我会将GoDownload方法更改为

private void GoDownload(Download Dnld, string[] urllist, EventArgs e) 
{
    foreach(string url in urllist) 
    {
        Dnld.Dnld(url);

        // this is just to give more time to test the cancellation
        System.Threading.Thread.Sleep(500);

        // Check the cancellation after each download
        if (DnldBgWorker.CancellationPending) 
        {
            e.Cancel = true;
            return;
        }
    }
}

对于第二个问题,当代码在UI线程而不是后台线程上运行时,需要调用该方法。通过在ProgressChanged事件的事件处理程序中移动文本框更新,可以轻松实现这一点。要设置事件处理程序,需要将另一个属性设置为true

DnldBgWorker.WorkerReportsProgress = true;

并为ProgressChanged事件设置事件处理程序

DnldBgWorker.ProgressChanged += DnldBgWorker_ProgressChanged;

private void DnldBgWorker_ProgressChanged(object sender,    ProgressChangedEventArgs e)
{
    EditProcess.Text(String.Format("Downloaded: {0}\r\n", e.ProgressPercentage));
}

DnldBgWorker.ReportProgress(i);