使用進度將取消令牌添加到異步任務

Question

我使用下面的代碼在WPF頁面異步方式中執行耗時的操作以及向UI報告進度

    private void btnStart_Click(object sender, RoutedEventArgs e)
    {
        txt_importStatus.Text = "";
        var progress = new Progress<string>(progress_info =>
        {
            //show import progress on a textfield
            txt_importStatus.Text = progress_info + Environment.NewLine + "Please dont close this window while the system processing the excel file contents";              
        });
        // DoProcessing is run on the thread pool.
        await Task.Run(() => DoProcessing(progress));
    }

    public void DoProcessing(IProgress<string> progress)
    {

        //read an excel file and foreach excel file row
        foreach(excelrow row in excelrowlist)
        {
            //do db entry and update UI the progress like 
            progress.Report("Processed x number of records. please wait..");    
        }  
    }

現在我想添加一個額外的選項，在中間取消這個異步操作。為此我發現我必須添加以下選項

CancellationTokenSource tokenSource = new CancellationTokenSource();
CancellationToken token = tokenSource.Token;    
private void btnCacnel_Click(object sender, RoutedEventArgs e)
{
    tokenSource.Cancel();
}

但是如何將此tokenSource傳遞給我的DoProcessing調用以及如何在DoProcessing中處理取消

Answer 1

你其實並不需要的傳遞CancellationTokenSource到DoProcessing ，但只是CancellationToken 。

為了處理取消，您可以執行以下操作：

    public void DoProcessing(CancellationToken token, IProgress<string> progress)
    {
        //read an excel file and foreach excel file row
        foreach(excelrow row in excelrowlist)
        {
            if(token.IsCancellationRequested)
                break;

            //do db entry and update UI the progress like 
            progress.Report("Processed x number of records. please wait..");    
        }  
    }

在這種情況下，您需要在btnStart_Click創建取消令牌源。 如果不清楚，你需要這樣做：

    CancellationTokenSource tokenSource;

    private void btnStart_Click(object sender, RoutedEventArgs e)
    {
        txt_importStatus.Text = "";
        var progress = new Progress<string>(progress_info =>
        {
            //show import progress on a textfield
            txt_importStatus.Text = progress_info + Environment.NewLine + "Please dont close this window while the system processing the excel file contents";              
        });
        // DoProcessing is run on the thread pool.
        tokenSource = new CancellationTokenSource();
        var token = tokenSource.Token;
        await Task.Run(() => DoProcessing(token, progress));
    }