Checking if a MainWindow already exists

Question

I have a C#/WPF application that consists of a mainwindow and a system tray icon. I have configured App.xaml with ShutdownMode="OnExplicitShutdown" in order to keep the application running in the system tray upon closing the main window.

In the context menu of the system tray icon, I have menu items bound to methods that re-open the main Window:

private void SysTray_Information_Click(object sender, RoutedEventArgs e)
{
    var newWindow = new MainWindow();
    newWindow.Show();
    MainWindow.Focus();
}

I would like to add to these methods a check to see if the mainwindow is already being displayed (hasn't been closed). Otherwise it will be possible to open multiple copies of the mainwindow. How can I achieve this?

score 2 · Answer 1 · edited Dec 25 '22 at 21:11

2

A semaphore or a mutex would be appropriate at the application level. This code is for a WinForms app but I am sure it can be modified to suite your needs.

static void Main()
{
    System.Threading.Mutex appMutex = new System.Threading.Mutex(true, "MyApplicationName", out exclusive);
    if (!exclusive)
    {
        MessageBox.Show("Another instance of My Program is already running.","MyApplicationName",MessageBoxButtons.OK,MessageBoxIcon.Exclamation );
        return;
    }
    Application.Run(new frmMyAppMain());
    GC.KeepAlive(appMutex);
}

edited Dec 25 '22 at 21:11

Vizel Leonid

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answered Apr 24 '14 at 01:38

Ross Bush

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2
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Actually, I re-read your original post. This would work for your sys tray application. However, determining if the main form is active is different, sorry. – Ross Bush Apr 24 '14 at 01:43

score 1 · Answer 2 · answered Apr 24 '14 at 01:37

It sounds like you could use a static variable for this:

public class MainWindow : Window
{
    private static bool _isInstanceDisplayed = false;
    public static bool IsInstanceDisplayed() { return _isInstanceDisplayed; }
}

Set it to true when you load the window. Then you can check as needed using:

if (MainWindow.IsInstanceDisplayed()) { ... }

Checking if a MainWindow already exists

2 Answers2