c# - Windows 窗体 : UI threads flow with Show() and ShowDialog()

Question

在 Windows 窗体上开发解决方案时，我习惯于向用户展示持续的进展。我实现了带有连续进度条的简单虚拟窗口:

在解决方案树中，它与主窗口位于同一级别:

在做某事时显示持续进展的最简单的工作方法是以下代码。它有效:

//This method works
private void DoSomeBackgroundStuffWithShow()
{
    ContinuousProgressWindow continuousProgressWindow = 
        new ContinuousProgressWindow();
    BackgroundWorker backgroundWorker = new BackgroundWorker();
    backgroundWorker.DoWork += (sender, arguments) =>
    {
        //Do some  stuff for 4 seconds
        Thread.Sleep(4000);
    };
    backgroundWorker.RunWorkerCompleted += (sender, arguments) =>
    {
        //Window is closed when needed. Great!
        continuousProgressWindow.Dispose(); 
    };
    continuousProgressWindow.Show(this);
    backgroundWorker.RunWorkerAsync();
}

但我需要此窗口显示在最顶层 并在工作时阻止其父窗口。以下代码非常相似，但它不起作用 - 显示对话框，但从未关闭:

//This method DOES NOT WORK
private void DoSomeBackgroundStuffWithShowDialog()
{
    ContinuousProgressWindow continuousProgressWindow =
        new ContinuousProgressWindow();
    BackgroundWorker backgroundWorker = new BackgroundWorker();
    backgroundWorker.DoWork += (sender, arguments) =>
    {
        //Do some important stuff for 4 seconds
        Thread.Sleep(4000);
    };
    backgroundWorker.RunWorkerCompleted += (sender, arguments) =>
    {
        //None of the following work for "ShowDialog() method"
        //Ran with debugger - breakpoints not hit!
        continuousProgressWindow.DialogResult = DialogResult.OK;
        continuousProgressWindow.Close();
        continuousProgressWindow.Dispose();
    };
    continuousProgressWindow.ShowDialog(this);
    backgroundWorker.RunWorkerAsync();
}

然后，我意识到问题出在 UI 线程流上:当进度窗口作为对话框运行时，MainWindow 线程被卡住，它无法被 BackgroundWorker 调用在 RunWorkerCompleted 委托(delegate)中关闭对话框。

让它按需工作的最简单解决方案是什么？

Answer 1

  continuousProgressWindow.ShowDialog(this);
  backgroundWorker.RunWorkerAsync();

您遇到了一个简单的先有鸡还是先有蛋的问题，直到对话框关闭之后您才启动 worker。 ShowDialog() 是一个阻塞调用。所以 RunWorkerCompleted 事件不会触发，因为工作人员没有开始。最简单的解决方法是交换两个语句:

  backgroundWorker.RunWorkerAsync();
  continuousProgressWindow.ShowDialog(this);

这样做并不完全安全。此代码段没有问题，但在实际代码中存在工作人员在显示对话框之前完成的危险。赔率低但不为零。要解决这个问题，您需要延迟 worker，直到您确定对话已启动并正在运行。这可以通过对话框的 OnShown() 方法使用 Set() 的 AutoResetEvent 来完成。或者，更优雅地，利用一个技巧:

  this.BeginInvoke(new Action(() => backgroundWorker.RunWorkerAsync()));
  continuousProgressWindow.ShowDialog(this);

Control.BeginInvoke() 的委托(delegate)目标在程序重新进入消息循环时运行。这发生在对话框变得可见之后:)