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Application.MainWindow Property


Gets or sets the main window of the application.

 property System::Windows::Window ^ MainWindow { System::Windows::Window ^ get(); void set(System::Windows::Window ^ value); };
public System.Windows.Window MainWindow { get; set; }
member this.MainWindow : System.Windows.Window with get, set
Public Property MainWindow As Window

Property Value

A Window that is designated as the main application window.


MainWindow is set from an application that's hosted in a browser, such as an XAML browser applications (XBAPs).


The following example shows how to find the main application window.

// Get the main window
Window mainWindow = this.MainWindow;
' Get the main window
Dim mainWindow As Window = Me.MainWindow

The following example shows how to set MainWindow using XAML.

    <NavigationWindow Source="MainPage.xaml" Visibility="Visible"></NavigationWindow>

The following example shows how to instantiate the MainWindow in code during application startup.

public partial class App : Application
    void App_Startup(object sender, StartupEventArgs e)
        MainWindow window = new MainWindow();
Partial Public Class App
    Inherits Application
    Private Sub App_Startup(ByVal sender As Object, ByVal e As StartupEventArgs)
        Dim window As New MainWindow()
    End Sub
End Class


MainWindow is automatically set with a reference to the first Window object to be instantiated in the AppDomain.

You can specify a different main window by setting MainWindow assigning another Windows object to the MainWindow property.

If the ShutdownMode property of the Application object is set to OnMainWindowClose, closing the main window causes the application to shut down.

It is possible to set the MainWindow property from XAML, if an application's main window is not the window that is produced by setting the StartupUri property in XAML. The two limitations of the XAML approach are:

  • You can specify either a XAML-only Window or a XAML-only NavigationWindow as the main window.

  • You must set the Visibility property of the window you specify, otherwise it won't be shown.

The reference to the first Window object to be instantiated is also added as the first item to the Windows collection. If MainWindow is subsequently set with a reference to a different Window, the position of the item with the reference to the main window will change, while the order of items in Windows remains the same. Consequently, always use MainWindow to refer to the main window instead of the first item in Windows.


If the main window is a NavigationWindow, and you need specific access to NavigationWindow members, you will need to cast the value of MainWindow to NavigationWindow.

This property is available only from the thread that created the Application object.

Applies to

See also