Multiple XamlRoots improvements

[MartinZikmund]

What would you like to be added:

• Determine whether InvalidateParentMeasureDirtyPath and InvalidateParentArrangeDirtyPath should use VisualTree.GetParent as fallback? feat: Enable multiple XamlRoots #8612 (comment)
• Enable drag and drop for multiple XamlRoots (see TODO in WpfDragDropExtension.cs - but will require changes on all platforms), choose proper XamlRoot in DropUITarget.cs (related fix: Fix DragDrop not working properly with multi window #16583)
• Add proper implementation for IXamlMetadataProvider and IXamlMetadataContainer members to Uno.UI.XamlHost.XamlApplication class.
• Pointer capture should capture the proper pointer type (mouse vs. pen vs. touch) (see dev/mazi/wip-wpf-capture) - as part of this also remove Capture methods from ICoreWindowExtension in favor of just using IPointerExtension
• Skia rendering - InvalidateRender - ensure invalidation is performed only for dirty rects
• Focus management support for non-CoreWindow XAML roots + we need to make sure that when the UnoXamlHost loses focus, focus is changed in the XamlRoot as well [focus]
• DependencyObjectExtensions.GetVisualTree and SetVisualTree should work on non-UIElements as well
• Adjust XamlRoot to support multiple windows ([windows] in XamlRoot.cs)
• Find a way to avoid using MetadataProviderDiscovery.MetadataProviderFactory
• UnoXamlHostBase.Layout.cs IsXamlContentLoaded parent is not set the same as in UWP
• Find out how to avoid the need for UpdateUnoSize() method in UnoXamlHostBase.Layout.cs
• Undo Uno specific approach in UnoTypeFectory.cs CreateXamlContentByType
• XamlRoot setter should work if XamlRoot property is still null (UIElement.cs XamlRoot property)
• DiscoverMetadataProviders was yield breaking after finding a Application type, why? [Question] Why break after Application type found? CommunityToolkit/Microsoft.Toolkit.Win32#347
• Unify and move Arrange and Measure invalidation code to use XamlRoot on all targets (e.g. #ifs in UIElement.Layout.netstd.cs)
• Investigate if there is a better way to associate target host InvalidateRender with XamlRoot (currently happening on Window.Activated for CoreWindow roots)
• FrameIdProvider should be in sync with actual frame rendering (should increase on each render)
• Refactor HostPointerHandler in WPF runtime
• Refactor inputs to simplify them, see feat: Enable multiple XamlRoots #8612 (comment)
• Get rid of CoreWindowContentRootSet and find a better way to notify about assigned XamlRoot (for both CoreWindow and XamlIslands)
• Determine whether the ditochomy of XamlRoot and GetOrCreateXamlRoot makes sense in ContentRoot and VisualTree
• Cleanup three first lines of code in UnoXamlHostBase.host.cs InitializeHost - they are required to properly initialize the application for islands use cases, but can't stay like this when we support multiple windows.
• Pointer handling going through CoreWindow is tricky and messy - https://github.com/unoplatform/uno/pull/8612/commits/ee8df80b3a92d916e0e8b7e36b1ba9d32e7548db\
• XamlRoot.Content currently supports only one window and its content for islands may not match UWP
• Adjust VisualTree.GetPopupRootForElement code to support XamlRoot
• Restore When_PlacementTarget_Binding when popups will be fully supported
• Tabbing out of an island to the parent app should be possible

Updated

• Unsubscribe from ApplicationView events on Window close in UnoGtkWindow and UnoWpfWindow
• Enable UWP-style new window via WUX AppWindow and add this to samples app
• Transition all targets to use non-CoreWindow windows in WinUI branch (Window.cs constructor)
• Invalidate and render each composition root independently
• Avoid having Dispatcher.Main and DispatcherQueue.Main
• Avoid Window.CurrentSafe reference in BackdropMaterial.cs based on updated WinUI sources
• Avoid using CoreWindow in FrameBuffer Uno.Templates Program.cs
• The events of Window should be changed to TypedEventHandlers on MUX source tree
• Avoid using CoreWindowActivationState in MUX source tree in favor of WindowActivationState
• Ensure EnteredBackground and LeavingBackground is raised in a platform agnostic way and respects multiwindow environment
• CoreWindow should not use WindowChrome (see ContentManager.cs)
• Verify whether we can use the same ScheduleInvalidateMeasureOrArrange(invalidateMeasure: true); for WASM in XamlRoot.crossruntime.cs or we need to keep the WASM-specific implementation
• Avoid __IOS__ specific workaround in ContentManager.cs (resetting the Frame after content changes)
• XamlRoot.Size and Bounds should forward to VisualTree.Size and VisualTree.Bounds and they should have aligned meaning Properly align window bounds and visible bounds readings #13975
• Add multi-XamlRoot support for drag and drop #13982
• Avoid using Window.CurrentSafe in FocusManager.wasm
• Add a way to identify which window is currently focused (active - should match the activation state)
• Get rid of all usages of GtkHost.InitialWindow and NativeWindowShown
• Get rid of all usages of WpfHost.InitialWindow and NativeWindowShown
• Empty Current Window Bounds if it's not Loaded #13118
• Window_SetBackground sample should apply to actual displayed Window not Window.Current
• Install snooper only once and route to currently focused window for GtkKeyboardInputSource.cs
• WpfDisplayInformationExtension should get DPI per window
• Re-enable commented out Given_Flyout tests
• Windows must be correctly cleaned up when closed and their XamlRoot collected
• Closing last window must terminate the application
• Window Bounds must be non-empty even before activation

Why is this needed:

For which Platform:

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• macOS
• Skia
  • WPF
  • GTK (Linux)
  • Tizen
• Windows
• Build tasks
• Solution Templates

Anything else we need to know?