CODEWITHSUNDEEP
c#.netwinforms
Juan
Juan

Reputation: 15715

Why is this code making my form disappear?

Since I added a splash screen my main form will sometimes (about 1 every 20 times) disappear like it's minimized (it will be invisible but it will be still on the task bar and if I click it it reappears). Here is my code:

static class Program
{
    private static SplashScreen splashScreen = null;
    private static ManualResetEvent splashScreenWaiter = null;
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        ShowSplashAsync();
        BuilderForm2 builderForm2 = new BuilderForm2();
        builderForm2.Shown += new EventHandler(builderForm2_Shown);
        Application.Run(builderForm2);
    }

    private static void HideSplash()
    {
        if (splashScreenWaiter != null)
        {
            splashScreenWaiter.WaitOne();
            splashScreen.Invoke(new Action(splashScreen.Close));
            splashScreenWaiter = null;
            splashScreen = null;
        }
    }

    private static void builderForm2_Shown(object sender, EventArgs e)
    {
        HideSplash();
    }

    private static void ShowSplashAsync()
    {
        splashScreenWaiter = new ManualResetEvent(false);
        Thread splashThread = new Thread(ShowSplash);
        splashThread.IsBackground = true;
        splashThread.SetApartmentState(ApartmentState.STA);
        splashThread.Start(splashScreenWaiter);
    }

    private static void ShowSplash(object resetEvent)
    {
        splashScreen = new SplashScreen((ManualResetEvent)resetEvent);
        Application.Run(splashScreen);
    }
}

And this is SplashScreen code:

public partial class SplashScreen : Form
{
    private ManualResetEvent ResetEvent;
    bool handleCreated = false;
    bool formShown = false;

    public SplashScreen(ManualResetEvent resetEvent)
    {
        ResetEvent = resetEvent;
        HandleCreated += new EventHandler(SplashScreen_HandleCreated);
        InitializeComponent();
    }

    private void SetResetEventIfReady()
    {
        if(handleCreated && formShown) ResetEvent.Set();
    }

    private void SplashScreen_Shown(object sender, EventArgs e)
    {
       formShown = true;
       SetResetEventIfReady();
    }

    void SplashScreen_HandleCreated(object sender, EventArgs e)
    {
        handleCreated = true;
        SetResetEventIfReady();
    }
}

Upvotes: 0

Views: 659

Answers (1)

Hans Passant
Hans Passant

Reputation: 941277

Nothing jumps out. There is however a very serious race condition in your code. It is related to the SystemEvents class. That class provides important notifications to controls so they can respond to the user changing the Windows theme. That class needs a hidden notification window to receive messages about the changes the user made.

This goes very wrong if your program's first window is created on a worker thread instead of the UI thread. That makes the SystemEvents class create that notification window on the wrong thread (not your worker thread btw). And the events it raises will be called from that thread. Getting the event on that wrong thread creates havoc, controls are not thread-safe. The most typical outcome is that you'll have odd painting problems or the form deadlocks when you lock the workstation. I can imagine what you see going wrong could be explained by this as well.

The .NET framework already has excellent and time-tested support for splash screens. I recommend you use it instead of spinning your own. Check this answer for the code.

If you want to keep your own then you can work around the race problem by pasting this line of code into your Main method, before the ShowSplashAsync call:

  Microsoft.Win32.SystemEvents.UserPreferenceChanged += delegate { };

Upvotes: 4

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