`LayoutUpdated` event is not fired properly

dr1rrb commented 3 years ago

Current behavior

The LayoutUpdated event is fired only on elements that has been [re-]layouted

Expected behavior

It's like a static event that has to be fired on any UIElement associated to the current thread
The sender of the event has to be null

More info: https://docs.microsoft.com/en-us/uwp/api/windows.ui.xaml.frameworkelement.layoutupdated?view=winrt-20348#remarks

How to reproduce it (as minimally and precisely as possible)

In a blank app, in the MainPage constructor, add

new Border().LayoutUpdated += (snd, e) => "".ToString();

The event handler is never invoked while it's on UWP!

Workaround

Don't rely on the sender like on UWP
Subscribe to Window.Current.Content.LayoutUpdated to get notify also for element that are not in the visual tree.

Works on UWP/WinUI

Yes

Environment

Uno.UI / Uno.UI.WebAssembly / Uno.UI.Skia

NuGet package version(s)

3.10.0-dev.632

Affected platforms

iOS, Android, WebAssembly, WebAssembly renderers for Xamarin.Forms, macOS, Skia (WPF), Skia (GTK on Linux/macOS/Windows), Skia (Tizen)

IDE

No response

IDE version

No response

Relevant plugins

No response

Anything else we need to know?

Didn't really validated on all platforms ... just an assumption based of current implementation.

jeromelaban commented 3 years ago

Youssef1313 commented 8 months ago

Wrote two runtime tests for this to prepare after #14936.

        [TestMethod]
        [RunsOnUIThread]
        public async Task When_LayoutUpdated()
        {
            string s = "";
            var button = new Button();
            button.LayoutUpdated += (sender, args) =>
            {
                Assert.IsNull(sender);
                Assert.IsNull(args);
                s += "button1 ";
            };
            button.LayoutUpdated += (sender, args) =>
            {
                Assert.IsNull(sender);
                Assert.IsNull(args);
                s += "button2 ";
            };

            var border = new Border
            {
                Width = 100,
                Height = 100,
                Background = new SolidColorBrush(Colors.Red),
            };

            border.LayoutUpdated += (sender, args) =>
            {
                Assert.IsNull(sender);
                Assert.IsNull(args);
                s += "border1 ";
            };

            border.LayoutUpdated += (sender, args) =>
            {
                Assert.IsNull(sender);
                Assert.IsNull(args);
                s += "border2 ";
            };

            await UITestHelper.Load(border);

            // On WinUI, running the test randomly produces one of these outputs.
            if (s is not ("button1 button2 border1 border2 " or "border1 border2 button1 button2 "))
            {
                Assert.Fail($"Test failed. Actual: {s}");
            }
        }

        [TestMethod]
        [RunsOnUIThread]
        public void When_LayoutUpdated_Element_Can_Get_GCed()
        {
            WeakReference GetButtonWeakReference()
            {
                var button = new Button();
                button.LayoutUpdated += static (_, _) => { };
                return new WeakReference(button);
            }

            var weakRef = GetButtonWeakReference();
            GC.Collect();
            Assert.IsFalse(weakRef.IsAlive);
        }

Youssef1313 commented 3 months ago

Done for Skia and Wasm in #16761

unoplatform / uno