WinUI 3 Fullscreen

Hello @Little Athan ,
Welcome to Microsoft Q&A!

Full screen can be used in winui3.
The usage of full screen is mentioned in the document Migrate from UWP to the Windows App SDK.

• Use AppWindow.SetPresenter with AppWindowPresenterKind.FullScreen.

Here is an example of button event triggering full screen,(It is recommended to use the latest Windows App SDK 1.1)

using Microsoft.UI;  
using Microsoft.UI.Windowing;  
using Microsoft.UI.Xaml;  
using Microsoft.UI.Xaml.Controls;  
using Microsoft.UI.Xaml.Controls.Primitives;  
using Microsoft.UI.Xaml.Data;  
using Microsoft.UI.Xaml.Input;  
using Microsoft.UI.Xaml.Media;  
using Microsoft.UI.Xaml.Navigation;  
using System;  
using System.Collections.Generic;  
using System.IO;  
using System.Linq;  
using System.Runtime.InteropServices.WindowsRuntime;  
using Windows.Foundation;  
using Windows.Foundation.Collections;  
  
using WinRT.Interop;  
  
// To learn more about WinUI, the WinUI project structure,  
// and more about our project templates, see: http://aka.ms/winui-project-info.  
  
namespace Winui3FullScreen  
{  
    /// <summary>  
    /// An empty window that can be used on its own or navigated to within a Frame.  
    /// </summary>  
    public sealed partial class MainWindow : Window  
    {  
        private AppWindow _appWindow;  
        public MainWindow()  
        {  
            this.InitializeComponent();  
            _appWindow = GetAppWindowForCurrentWindow();  
        }  
  
        private void myButton_Click(object sender, RoutedEventArgs e)  
        {  
            myButton.Content = "Clicked";  
            if (_appWindow.Presenter.Kind == AppWindowPresenterKind.FullScreen)  
            {  
                _appWindow.SetPresenter(AppWindowPresenterKind.Default);  
                myButton.Content = "Full Screen";  
            }  
            else  
            {  
                _appWindow.SetPresenter(AppWindowPresenterKind.FullScreen);  
                myButton.Content = "Exit Full Screen";  
            }  
        }  
  
        private AppWindow GetAppWindowForCurrentWindow()  
        {  
            IntPtr hWnd = WindowNative.GetWindowHandle(this);  
            WindowId myWndId = Win32Interop.GetWindowIdFromWindow(hWnd);  
            return AppWindow.GetFromWindowId(myWndId);  
        }  
    }  
}  

Thank you.

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