c# - 保持 Form 实例打开的任务？

Question

我有一个 Windows 窗体可以打开另一个窗体。在次要形式中，它异步启动任务。如果用户启动任务然后取消它并快速关闭表单，表单将被处理并设置为 null 但是当任务从被取消中恢复时我仍然会收到 MessageBox.Show 发生

public class MyMainForm : Form
{
  public void OpenChildForm()
  {
     MyChildForm form = new MyChildForm();
     form.ShowDialog();
     form.Dispose();
     form = null;
  }
}

public class MyChildForm : Form
{

  private CancellationTokenSource MyTokensource;
  private Task task; 


  public void StartTask()
  {
     MyTokensource = new CancellationTokenSource();
     task = Task.Factory.StartNew(() => MyMethod(MyTokensource.Token), MyTokensource.Token);
  }

  public void MyMethod(CancellationToken token)
  {
      var result = StaticClass.DoSomethingLengthy(token);  //The cancel make take a couple of seconds to return here
      if (result == Cancelled)
      {
         MessageBox.Show("Cancelled");
         UpdateLabel("Cancelled")
       }
  }

  public void ButtonClose_Click()
  { 
    if (task != null && !task.IsCompleted)
    {
      MyTokensource.Cancel();
    }
    this.Close();
  }
}

Answer 1

the form is Disposed and set to null however when the task comes back from being cancelled I still get a MessageBox.Show happen

将作为表单引用的变量设置为 null，甚至在表单上调用 Dispose()，实际上销毁表单。 Task 仍在执行，直到它被取消(CancellationTokenSource 被设计为用于取消的协作模型)。

因此，您需要显式处理取消任务时出现的代码路径。这可能就像检查您是否已经处置一样简单，即:

if (this.IsDisposed)
    return; // Just break out if we canceled and shut down

// Your other code....
if (result == Cancelled)
    MessageBox.Show("Cancelled");