System.Windows.MessageBox doesn't wait for user input before going poof!

...and it makes no sense why. T-T

In my Application_Startup event handler I have code that looks kinda like this:

private void Application_Startup(object sender, StartupEventArgs e)
{
    string errorMessage;

    if(CheckStartUpConditions(out errorMessage))
    {
        (new MainWindow()).Show();
    }
    else
    {
        MessageBox.Show(errorMessage, "Application Startup", 
            MessageBoxButton.OK, MessageBoxImage.Error);

        Shutdown();
    }
}

private bool CheckStartUpConditions(out string errorMessage)
{
    errorMessage = string.Empty;  

    if(...)
        errorMessage += "Please login to xxx. ";

    if(...)
        errorMessage += "Please install xxx.";

    if(string.IsNullOrEmpty(errorMessage))
        return true;
    else
        return false;
}

The message box makes an brief appearance for like a second before going "POOF!" It doesn't wait for me to click "OK" or on the "X" button. I'm really stumped as to why this is occuring, so any help would be greatly appreciated.

I've tried commenting out the call to Shutdown just for kicks and giggles, and it still behaves the same way.

Also, the application also has a SplashScreen, so I don't know if that's effecting this.

EDIT: I added more code if that helps. The message box is showing the correct error message. Just won't stay long enough for the users to read it. >:(

EDIT PART 2: Okay...I think I've found the culprit. :( I changed the build action on the image I'm using as my splash from SplashScreen to None and the message box will now stay and wait for user input. I don't understand why the SplashScreen is screwing with the MessageBox. >:(

Alexey Ivanov

Try to use an overload that accepts System.Windows.Window parameter and pass Null value to make your MessageBox a top-level window of your application, which is independent of all other windows that may exist. I guess your MessageBox gets owned by splashscreen form. When splashscreen is closed, the framework closes the MessageBox. So making your MessageBox ownerless should do the trick.

Based on Alexey Ivanov's suggestion, I successfully used a new window as the parent

System.Windows.Forms.MessageBox.Show(new System.Windows.Forms.NativeWindow(), errorMessage, "Application Startup", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);

The message box vanishes immediately because it has no owner. If you specify the option MessageBoxOptions.DefaultDesktopOnly, the desktop will be assigned as the owner, and the message box will work correctly on an application with no main window.

MessageBox.Show(
    "Message", 
    "Title",
    MessageBoxButton.YesNoCancel, 
    MessageBoxImage.Question, 
    MessageBoxResult.Cancel,
    MessageBoxOptions.DefaultDesktopOnly);

Create transparent hidden window and use it as an owner of the MessageBox:

private Window CreateHiddenWindow()
        {
            var window = new Window
            {
                AllowsTransparency = true,
                Background = System.Windows.Media.Brushes.Transparent,
                WindowStyle = WindowStyle.None,
                Top = 0,
                Left = 0,
                Width = 1,
                Height = 1,
                ShowInTaskbar = false
            };

            window.Show();

            return window;
        }

You can keep your splash screen and use a standard WPF MessageBox if you implement the splash screen in code instead of as an image build action.

App.xaml.cs:

var splashScreen = new SplashScreen("path/to/splash_image.bmp");
splashScreen.Show(false); //make sure to use 'false' here to prevent auto-closing

string errorMessage;

if(CheckStartUpConditions(out errorMessage))
{
    (new MainWindow()).Show();
}
else
{
    //standard WPF MessageBox may now be used here
    MessageBox.Show(errorMessage, "Application Startup", 
        MessageBoxButton.OK, MessageBoxImage.Error);

    Shutdown();
}

//explicitly close the splash screen now
splashScreen.Close(TimeSpan.FromSeconds(1));

Alexey is right, the splash screen closes the message box.

A simple way to avoid this is to use the native MessageBox function:

[DllImport("user32.dll", CharSet = CharSet.Unicode)]
public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);

public static void Main()
{
   ...
   MessageBox(new IntPtr(0), "Hello World!", "MyApp", 0);

You need to tell WPF not to shutdown when the first window does. Look at this: http://msdn.microsoft.com/en-us/library/system.windows.application.shutdownmode.aspx. You want to set your application to shutdown explicitly (instead of after the first window closes):

<Application
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    StartupUri="MainWindow.xaml"
    ShutdownMode="OnExplicitShutdown">
</Application>

Your other choose is to set your MainWindow as the StartupUri (instead of your splash screen) and then load your splash screen in the MainWindow's loaded event. Then you would do whatever loading or time intensive stuff you need to do, hide your splash screen, and re-show your main Window.

来源：https://stackoverflow.com/questions/5923188/system-windows-messagebox-doesnt-wait-for-user-input-before-going-poof

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