Opening all windows at the same time

Question

I found this post searching

https://learn.microsoft.com/en-us/answers/questions/1411868/how-to-activate-a-window-in-net-maui

it seems like a good solution

 if (!WindowHelper.SecondWindowCreated) {
        // Create the second window
        var newPage = _items[name!];
        var secondWindow = WindowHelper.CreateWindow(newPage, "second", 300, 300);
        secondWindow.Created += (s, e) => { WindowHelper.SecondWindowCreated = true; };
        secondWindow.Destroying += (s, e) => { WindowHelper.SecondWindowCreated = false; };
        Application.Current?.OpenWindow(secondWindow);
    } else {
        // Activate the existing second window
        MauiProgram.secondWindow.Activate();
    }

it does open the correct window, it is opening the same every time

        public static MauiWinUIWindow secondWindow;
        public static MauiApp CreateMauiApp() {
            var builder = MauiApp.CreateBuilder();
            builder
                .UseMauiApp<App>()
                .ConfigureFonts(fonts => {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
                }).ConfigureLifecycleEvents(e => {
#if WINDOWS
                    e.AddWindows(windows => windows.OnWindowCreated(window => {
                        var mauiWinUIWindow = window as MauiWinUIWindow;
                        if (mauiWinUIWindow?.Title == "second") {
                            secondWindow = mauiWinUIWindow;
                        }
                    }));
#endif
                });
#if DEBUG
            builder.Logging.AddDebug();
#endif
            builder.Services.AddTransient<MainViewModel>();
            builder.Services.AddSingleton<MainPage>();

 public static bool SecondWindowCreated { get; set; }

 public static Window CreateWindow(Page view, string title, double height, double width, double x = 0, double y = 0) {

     var displayInfo = DeviceDisplay.MainDisplayInfo;

     if (height == 0 && width == 0) {

         width = displayInfo.Width;
         height = displayInfo.Height;
     }

     var newWindow = new Window() {

         Page = view,

         Title = title,

         Height = height,

         Width = width,

         X = x,

         Y = y,

     };

     return newWindow;
 }

If for example I have my application in Fullscreen move, and decide to open 8 little windows it will open all (Obviously I know that I have to click on them to interact with them, but a want to see all of them

look

I am going to open the "Marion Window"

if I click in the dot net

I get the Maio windows

I also found a bug, if I close the mario window and try to open it again. I get

apparenly my new Window is null

Answer 1

Hello,

Only one variable is needed to activate two windows. For multi-window requirements, you need to record the opened windows through a data structure. In the following example, I use two pages, differentiate them through different Title attributes and save them into a dictionary.

Before providing the key code, I need to explain two core issues.

If I open the Mario window, and close it, and open again I get this error.

This null pointer error is because you used a dictionary to create the page.

    Dictionary<string, Page> _items = new() {

        {"mario.png", new Page1()},
        {"dotnet_bot.png", new Page_2()},
    };

Your expected behavior should be to create a new page using the value in the ImageButton. However, the actual function of this code is to create a new page only when declared. So when you close the window and reopen it, the context will be null because the page has been Disposed.

every window I opened. for windows and Mac

Mac does not support programmatic activation of windows.

First of all, I would like to inform you that the user has to touch the screen to active a session on iOS/MacCatalyst. Please watch the Apple's Window Management in Your Multitasking App video around 4:50. Therefore, you cannot bring an existing window to the foreground programmatically.

For implementing this function on Windows, please refer to the following key code:

API you need to implement for WindowHelper.

  public static class WindowHelper
    {
        private static Dictionary<string, Window> _windows = new Dictionary<string, Window>();
#if WINDOWS
        private static Dictionary<string, MauiWinUIWindow> _windowsUIWindow = new Dictionary<string, MauiWinUIWindow>();
        public static void AddUIWindow(string title,MauiWinUIWindow value)
        {
            if (!_windowsUIWindow.ContainsKey(title))
            {
                value.Closed += (s, e) => {
                    _windowsUIWindow.Remove(title);
                };
                _windowsUIWindow.Add(title, value);
            }
        }
        public static MauiWinUIWindow GetExistedWinUIWindow(string title)
        {
            return _windowsUIWindow[title];
        }
#endif
        public static bool WindowCreated(string title)
        {
            return _windows.ContainsKey(title);
        }
        public static Window GetExistedWindow(string title) { 
            return _windows[title];
        }
        public static Window CreateWindow(Page view, string title, double height, double width, double x = 0, double y = 0)
        {
            if (!_windows.ContainsKey(view.Title))
            {
                var displayInfo = DeviceDisplay.MainDisplayInfo;

               if (height == 0 && width == 0)
                {

                   width = displayInfo.Width;
                    height = displayInfo.Height;
                }

               var newWindow = new Window()
                {
                    Page = view,
                    Title = title,
                    Height = height,
                    Width = width,
                    X = x,
                    Y = y,
                };
                newWindow.Destroying += (s, e) => { _windows.Remove(view.Title); };
                _windows.Add(view.Title, newWindow);
                return newWindow;
            }
            else
            {
                return _windows[view.Title];
            }

        }
   }

Add WinUI window to dictionary when creating new window:

.ConfigureLifecycleEvents(e => {
#if WINDOWS
                    e.AddWindows(windows => windows.OnWindowCreated(window => {
                        var mauiWinUIWindow = window as MauiWinUIWindow;
                        WindowHelper.AddUIWindow(mauiWinUIWindow.Title, mauiWinUIWindow);
                    }));
#endif
                });

Create a new page through the Switch method in the page to avoid the null pointer problem.

public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }
        Page GetPageByName(string Sourcename)
        {
            switch (Sourcename) {
                case "File: test.png":
                    return new Page1(); // 
                case "File: dotnet_bot.png":
                    return new Page2();
                default:
                    return new Page1();
            }
        }
        private void ImageButton_Clicked(object sender, EventArgs e)
        {
            var btn = sender as ImageButton;
            var newPage = GetPageByName(btn.Source.ToString());
            if (!WindowHelper.WindowCreated(newPage.Title))
            {
                // Create the new window
                var newWindow = WindowHelper.CreateWindow(newPage, newPage.Title, 300, 300);   
                Application.Current?.OpenWindow(newWindow);
            }
            else
            {
#if WINDOWS
                // Activate the existing second window
                WindowHelper.GetExistedWinUIWindow(newPage.Title).Activate();
#endif
            }
       }
    }

Best Regards,

Alec Liu.

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