在WPF中使用Backgroundworker弹出主应用程序的消息框

Question

在 WPF 应用程序中，我使用 BackgroundWorker 定期检查服务器上的情况。虽然这工作正常，但我想弹出一个消息框，如果检查过程中出现问题，通知用户。

这是我所拥有的：

public static void StartWorker()
{
    worker = new BackgroundWorker();

    worker.DoWork += DoSomeWork;
    worker.RunWorkerAsync();
}

private static void DoSomeWork(object sender, DoWorkEventArgs e)
{
    while (!worker.CancellationPending)
    {
        Thread.Sleep(5000);

        var isOkay = CheckCondition();

        if(!isOkay)
           MessageBox.Show("I should block the main window");                
    }   
}

但是这个MessageBox并不会遮挡主窗口。我仍然可以单击我的 WPF 应用程序并使用 MessageBox 更改我喜欢的任何内容。

我该如何解决这个问题？谢谢，

---

编辑：

仅供参考，这就是我最终所做的：

public static void StartWorker()
{
    worker = new BackgroundWorker();

    worker.DoWork += DoSomeWork;
    worker.ProgressChanged += ShowWarning;
    worker.RunWorkerAsync();
}

private static void DoSomeWork(object sender, DoWorkEventArgs e)
{
    while (!worker.CancellationPending)
    {
        Thread.Sleep(5000);

        var isOkay = CheckCondition();

        if(!isOkay)
           worker.ReportProgress(1);                
    }   
}

private static void ShowWarning(object sender, ProgressChangedEventArgs e)
{
    MessageBox.Show("I block the main window");
}

Answer 1

更换

MessageBox.Show("I should block the main window"); 

与

this.Invoke((Func<DialogResult>)(() => MessageBox.Show("I should block the main window")));

这将导致消息框位于主线程上，并阻止对 UI 的所有访问，直到收到响应。作为额外的好处， this.Invoke 将返回一个可以转换为 DialogResult 的对象。

Answer 2

它不但不会挡住主窗口，还很有可能消失在主窗口后面。这是它在不同线程上运行的直接结果。当您没有指定消息框的所有者时，它会使用 GetActiveWindow() API 函数寻找所有者。它只考虑使用相同消息队列的窗口。这是线程特定的属性。当然，丢失消息框是很难处理的。

同样，MessageBox 仅禁用属于同一消息队列的窗口。因此不会阻塞主线程创建的窗口。

通过让 UI 线程显示消息框来解决您的问题。使用 Dispatcher.Invoke 或利用 ReportProgress 或 RunWorkerCompleted 事件。听起来这些活动在这里不合适。

Answer 3

致电

ReportProgress

并将

this

传递给

MessageBox.Show

。

Answer 4

正如 Stephen 和 Hans 所说，使用 ReportProgress 事件，并将数据传递到 UI 线程。如果您想要执行 MessageBox 以外的任何操作（例如，更新控件），这一点尤其重要，因为后台线程无法直接执行此操作。你会得到一个跨线程异常。

因此，无论您需要做什么（更新进度条、向 UI 记录消息等），将数据传递给 UI 线程，告诉 UI 线程需要做什么，但让 UI 线程去做。

Answer 5

我像这样修改了它并且对我来说效果很好

 return Application.Current.Dispatcher.Invoke(() => MessageBox.Show(messageBoxText, caption, button, icon));

Answer 6

为有关使用 ReportProgress 的建议添加一些技巧：

这是鱼与熊掌兼得的好方法！或者换句话说，这是一种让您在 BackgroundWorker

中编写 UI 交互代码并且不会遇到跨线程操作的方法。有一天我把这个放在一起做一个项目，买家要小心！

' Init background worker
Dim _BGWorker As BackgroundWorker

' Your Windows Form's _Load event handler:
Private Sub Form_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    ' Just for this example, we're newing up the _BGWorker here
    _BGWorker = New BackgroundWorker()
    _BGWorker.WorkerReportsProgress = True
End Sub

' Magical UI Action Handling ProgressChanged Event Handler Thing (v24.4.550-alpha9) ™ ©
Private Sub _BGWorker_ProgressChanged(ByVal sender As Object, ByVal e As ProgressChangedEventArgs) Handles _BGWorker.ProgressChanged
    ' Take the UserState object and cast to an Action delegate type
    Dim uiAction As Action = CType(e.UserState, Action)

    ' Check if an action was passed
    If uiAction IsNot Nothing Then
        ' Run it if so!
        uiAction()
    End If
End Sub

' Standard DoWork handler for BackroundWorker
Private Sub _BGWorker_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs) Handles _BGWorker.DoWork
    '...your background worker code...

    ' EXAMPLE:
    '
    ' Me.Text = "Background worker is (trying to) change form title! :-O"
    '
    ' This line would normally fail with an exception when written directly in the DoWork
    ' handler of a BackgroundWorker. Exception you would see is:
    '   System.InvalidOperationException: Cross-thread operation not valid: Control 'FormName'
    '   accessed from a thread other than the thread it was created on.'

    ' BUT...

    ' If we write something like this:

    _BGWorker.ReportProgress(-1, New Action(
    Sub()
        '...and put that line inside this action:
        Me.Text = "Background worker is changing form title! :-O"

        ' Then NO PROBLEM! UI-interactive code MAGIC!

        ' Well, it's not magic... This works because this code is not executed here immediately.
        ' It is an Action Delegate: https://learn.microsoft.com/en-us/dotnet/api/system.action-1?view=net-7.0
        ' You can write ANY UI-interactive code inside blocks like this in your BackgroundWorkers
        ' and they will all execute on the main thread, because the Action delegate is being 
        ' shipped to the ProgressChanged event handler on the main Form thread.

        'TODO: Add your other UI code...

    End Sub))

    ' Now simply repeat the above section every time you wish write UI-interactive
    ' code in your BG workers! SHAZAM!

    '...your background worker code...
End Sub