[Foda]

Description of Change

Currently (on Windows), DeviceDisplay.Current.MainDisplayInfo doesn't get set until the first window is activated/shown on the screen since it uses the active window to gather this info.

This PR fixes that by setting the active window as soon as possible using the OnPlatformWindowSubclassed lifecycle event. This lifecycle event happens after we have a valid HWND but before the window is "technically" active. I don't think this will cause any issues (???).

As a result, Windows users can now do things like override Application.CreateWindow to set the initial window position and size before it's shown without needing to pinvoke:

class App : Application
{
    protected override Window CreateWindow(IActivationState activationState)
    {
        Window window = new Window(new NavigationPage(new MainPage()));

        var disp = DeviceDisplay.Current.MainDisplayInfo;
        var newWidth = disp.Width / 2;
        var newHeight = disp.Height / 2;

        // center the window
        window.X = (disp.Width / disp.Density - newWidth) / 2;
        window.Y = (disp.Height / disp.Density - newHeight) / 2;

        return window;
    }
}

Issues Fixed

Fixes #6976

[jfversluis]

I think a lot of people will be happy with this one, thank you!

[rmarinho]

Can we name the files for test like the other ones, no underscores please.

[Foda]

Thanks for applying the code review suggestions @jfversluis!

[kt215]

How will I know which maui-windows workload version this fix will be included in? The latest version is 7.0.81/7.0.100

[gerneio]

Would also like to know what version this fix will be applied to? Is this being saved for .NET 8? Hopefully will be delivered sooner. Can confirm that it's still an issue in the latest maui-windows workload version.

[mattleibow]

I wonder if we should actually take a different approach. If there is no main window yet, then we can just use the main monitor on the system?

I suppose the event is useful generally as it forms the same thing as an activity OnCreate...

[dinther]

It's day two of me exploring .NET Maui ... And I run into fundamental stuff like this!

The workaround solution offered here #6976 (comment)
is of no use as it assumes a displayDensity of 1

When will the fix be released?

Here is another workaround. My issue is the redraw of the window that appears as flashing. But setting the window size to 0 in createWindow and then to the proper size and location in the Loaded event handler of the Page works.

App.xaml.cs

namespace MyApp
{
    public partial class App : Application
    {
        double displayWidth;
        public App()
        {
            InitializeComponent();
            MainPage = new AppShell();
        }
        protected override Window CreateWindow(IActivationState activationState)
        {
            Window window = base.CreateWindow(activationState);
            // Manipulate Window object
            window.Width = 0;
            window.Height = 0;
            return window;
        }
    }
}

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.MainPage"
             Loaded="OnPageLoaded">

             ....

using Microsoft.Maui.Controls;

namespace MyApp
{
    public partial class MainPage : ContentPage
    {
        int count = 0;

        public MainPage()
        {
            InitializeComponent();
        }

        private void OnPageLoaded(object sender, EventArgs e)
        {
            // Get display size
            var displayInfo = DeviceDisplay.Current.MainDisplayInfo;
            Window.Width = 1700;
            Window.Height = 1500;
            // Center the window
            Window.X = (displayInfo.Width / displayInfo.Density - Window.Width) / 2;
            Window.Y = (displayInfo.Height / displayInfo.Density - Window.Height) / 2;
        }

         ....