WPF : How to set a Dialog position to show at the center of the application?

Question

How to set Dialog\'s position that came from .ShowDialog(); to show at the center of the mainWindows.

This is the way I try to set position.

Answer 1

This code works if you don't want to use the WindowStartupLocation property in xaml:

private void CenterWindowOnApplication()
{
    System.Windows.Application curApp = System.Windows.Application.Current;
    Window mainWindow = curApp.MainWindow;
    if (mainWindow.WindowState == WindowState.Maximized)
    {
        // Get the mainWindow's screen:
        var screen = System.Windows.Forms.Screen.FromRectangle(new System.Drawing.Rectangle((int)mainWindow.Left, (int)mainWindow.Top, (int)mainWindow.Width, (int)mainWindow.Height));
        double screenWidth = screen.WorkingArea.Width;
        double screenHeight = screen.WorkingArea.Height;
        double popupwindowWidth = this.Width;
        double popupwindowHeight = this.Height;
        this.Left = (screenWidth / 2) - (popupwindowWidth / 2);
        this.Top = (screenHeight / 2) - (popupwindowHeight / 2);
    }
    else
    {
        this.Left = mainWindow.Left + ((mainWindow.ActualWidth - this.ActualWidth) / 2;
        this.Top = mainWindow.Top + ((mainWindow.ActualHeight - this.ActualHeight) / 2);
    }
}

I am using "screen.WorkingArea" because the task bar makes the mainWindow smaller. If you want to place the window in the middle of the screen, you can use "screen.Bounds" instead.

Answer 2

In the XAML belonging to the Dialog:

<Window ... WindowStartupLocation="CenterOwner">

and in C# when you instantiate the Dialog:

MyDlg dlg = new MyDlg();
dlg.Owner = this;

if (dlg.ShowDialog() == true)
{
    ...