使用ShowDialog（）从STA线程显示窗口

Question

I need to open a window from a dll project (Runs in the background or is triggered when called). For this to be possible I need to open a window from a method marked as [STAThread] to create an instance of the window.

I am using the MVVM pattern to bind the ViewModel to a View, and the view is added to the MainWindow as a usercontrol.

On the View there is a button bound to a command that 'closes' the window. The command in the ViewModel calls the CloseCommand(), which in turn will call the window.Close() method.

Code Snippet:

    MethodShowingTheWindow() {
        var idVM = new IDWindowViewModel();
        ShowForm<MainWindow>(idVM); // Works fine, Close Command closes the window.
        ShowForm<MainWindow>(idVM); // hits the ShowDialog() line, then just jumps to the while loop 
        ShowForm<MainWindow>(idVM);        // waiting for the thread to finish. Never displays the window.
        ShowForm<MainWindow>(idVM);

    }

    [STAThread]
    public void ShowForm<T>(IViewModel vm) {
        Thread th = new Thread(new ThreadStart(delegate {
            var window = new MainWindow();
            window.DataContext = vm;

            vm.CloseAction = new Action(() => window.Close()); // Does this when the Close Action is called from the viewmodel (Close the window).

            try {
                window.ShowDialog();
            } catch (Exception ex) {
                throw ex;
            }
        }));

        th.ApartmentState = ApartmentState.STA;
        th.Start();

        while (th.IsAlive) {
            //Wait for thread to finish
        }
    }

All I need to know is why the window wont appear with the second ShowWindow(idVM) call? All I can think of is that the Window is not correctly closed/Disposed. I tried adding the following to the CloseAction Action:

...
vm.CloseAction = new Action(() => {
    if (window is IDisposable) (window as IDisposable).Dispose();
    window.Close();
});

but (window is IDisposable) == false?

Any help would be greatly appreciated.

Answer 1

This is my implementation for your scenario. Using Dispatcher in order to avoid STA Exceptions:

async Task MethodShowingTheWindow() 
{
    var idVM = new IDWindowViewModel();
    await ShowForm<MainWindow>(idVM); // Works fine, Close Command closes the window.
    await ShowForm<MainWindow>(idVM); // hits the ShowDialog() line, then just jumps to the while loop 
    await ShowForm<MainWindow>(idVM);        // waiting for the thread to finish. Never displays the window.
    await ShowForm<MainWindow>(idVM);
}

public await Task ShowForm<T>(IViewModel vm) 
{
    Dispatcher.InvokeAsync(() =>
    {
        var window = new MainWindow();
        window.DataContext = vm;
        System.Windows.Application.Current.Dispatcher.Invoke(() =>
        {
            vm.CloseAction = new Action(() => window.Close());
        });
        window.ShowDialog();
    });
}