在另一个事件处理方法中取消已经初始化和运行的任务

Question

我正在构建一个 C#/Windows 表单应用程序。

在表单上各种按钮的点击事件处理程序中，我初始化并触发了不同的任务。但是，对于某些按钮单击，我想取消任何仍然运行由某些其他单击事件处理程序启动的任务。

下面是我的代码。到目前为止，第二个版本是我尝试使用第二种方法来取消第一种方法启动的运行任务，但是它还不起作用。如何取消运行任务？

示例代码（尚未添加取消令牌）：

private void btnFrontDoorCycle_Click(object sender, EventArgs e)
{
    Task.Factory.StartNew(() =>
    {
        // Do function 1
        // Do function 2
        // etc
    });
}

private void btnFrontDoorClose_Click(object sender, EventArgs e)
{
    // If task started in btnFrontDoorCycle_Click is running, cancel it here
    Task.Factory.StartNew(() =>
    {
        // Do function 5
        // Do function 6
        // etc
    });
}

示例代码（我尝试添加取消令牌时无法正常工作）：

private CancellationTokenSource cancellationTokenSource;
private void btnFrontDoorCycle_Click(object sender, EventArgs e)
{
    Task.Factory.StartNew(() =>
    {
        // Do function 1
        // Do function 2
        // etc
    }, cancellationToken);
}

private void btnFrontDoorClose_Click(object sender, EventArgs e)
{
    // If task started in btnFrontDoorCycle_Click is running, cancel it here
    if (this.cancellationTokenSource != null)
    {
        this.cancellationTokenSource.Cancel();
    }
    this.cancellationTokenSource = new CancellationTokenSource();
    CancellationToken cancellationToken = this.cancellationTokenSource.Token;
    Task.Factory.StartNew(() =>
    {
        // Do function 5
        // Do function 6
        // etc
    });
}

Answer 1

您是否在代码中检查 cancellationToken.IsCancelationRequested？我认为这就是问题所在。

应该是这样的：

// Do function 1
if (token.IsCancellationRequested)
{
    return;
}
// Do function 2
// Were we already canceled?
ct.ThrowIfCancellationRequested();// another variant
// etc

更多详情：https://msdn.microsoft.com/en-us//library/dd997396(v=vs.110).aspx

Answer 2

您需要检查令牌是否已被取消。下面是我编写的一小段代码，只是为了检查它是如何工作的。希望你能从中提取你需要的东西...

internal class TaskCancellationProblem
{
    private CancellationTokenSource tokenSource;
    private CancellationToken token;

    public TaskCancellationProblem()
    {
        ResetSourceAndToken();
    }

    private void ResetSourceAndToken()
    {
        tokenSource = new CancellationTokenSource();
        token = tokenSource.Token;
    }

    public void RunFirstTask()
    {
        // check if cancellation has been requested previously and reset as required
        if (tokenSource.IsCancellationRequested)
            ResetSourceAndToken();

        Task.Factory.StartNew(() =>
        {
            while (!token.IsCancellationRequested)
            {
                Console.WriteLine("Doing first task");
                Thread.Sleep(1000);
            }
        }, token);
    }

    public void CancelFirstAndRunSecond()
    {
        // Cancel the task that was running
        tokenSource.Cancel();
        Task.Factory.StartNew(() =>
        {
            while (true)
            {
                Console.WriteLine("Doing second task");
                Thread.Sleep(1000);
            }
        });
    }
}

在另一个事件处理方法中取消已经初始化和运行的任务

Cancel tasks that have been initialized and run in another event handler method

.net

c#

multithreading

task

winforms