在 BackgroundWorker 运行时显示模态窗口，而不会出现 STA/MTA 问题

Question

我正在开发一个 WPF 应用程序。我有一个耗时的方法，我想通过BackgroundWorker 运行异步。当方法运行时，我想显示一个模态的“请稍候...”对话框窗口，它必须在 BackgroundWorker 完成时自动关闭。

我目前对BackgroundWorker 或任何多线程编程的经验很少。

下面的代码当前生成InvalidOperationException，并带有消息“调用线程必须是 STA，因为许多 UI 组件都需要这个。”

请告诉我如何实现我想要实现的目标，如果你能帮助我了解问题所在，请给我额外的加分。

非常感谢！

编辑 澄清一下 - 这个想法是主线程启动BackgroundWorker，然后显示模式对话框。当工作人员完成时，它会关闭模式对话框。当模态对话框关闭时，主线程继续。

public class ImageResizer
{
    private BackgroundWorker worker;
    private MemoryStream ImageData { get; set; } // incoming data
    private public MemoryStream ResizedImageData { get; private set; } // resulting data
    private Dialogs.WorkInProgressDialog ProgressDialog;


    // Public interface, called by using class:
    public MemoryStream ReduceImageSize(MemoryStream imageData)
    {
        // injected data:
        this.ImageData = imageData;

        // init progress dialog window:
        ProgressDialog = new Dialogs.WorkInProgressDialog();

        // Start background worker that asyncronously does work
        worker = new BackgroundWorker();
        worker.DoWork += new DoWorkEventHandler(worker_DoWork);
        worker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(worker_RunWorkerCompleted);            
        worker.RunWorkerAsync();

        // Show progress dialog. Dialog is MODAL, and must only be closed when resizing is complete
        ProgressDialog.ShowDialog(); // THIS LINE CAUSES THE INVALID OPERATION EXCEPTION

        // This thread will only continue when ProgressDialog is closed.

        // Return result
        return ResizedImageData;
    }

    private void worker_DoWork(object sender, DoWorkEventArgs e)
    {
        // Call time consuming method
        ResizedImageData = ReduceImageSize_ActualWork();
    }

    // The actual work method, called by worker_DoWork
    private MemoryStream ReduceImageSize_ActualWork()
    {
        // Lots of code that resizes this.ImageData and assigns it to this.ResizedImageData
    }

    private void worker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {   
        // Async work completed - close progress dialog
        ProgressDialog.Close();
    }
}

Answer 1

您不能从 BackgroundWorker 调用 ShowDialog。您必须使用 Dispatcher 要求 UI 线程执行它：

 this.Dispatcher.BeginInvoke(new Action(() => ProgressDialog.ShowDialog()));

BackgroundWorker的'Completed'事件是在UI线程中执行的，所以这部分应该没问题。