[Windows] Fixed the flyout content width not being set correctly after updating to WinUI SDK 1.7 (#28996)

* Fixed flyout content width issue

* Updated details

Author: Tamilarasan-Paranthaman

src/Controls/src/Core/Handlers/Shell/Windows/ShellFlyoutItemView.cs

@@ -98,9 +98,6 @@ void ShellElementPropertyChanged(object sender, PropertyChangedEventArgs e)
 			if (ShellView == null)
 				return base.MeasureOverride(availableSize);
 
-			if (!ShellView.IsPaneOpen)
-				return base.MeasureOverride(availableSize);
-
 			if (ShellView.OpenPaneLength < availableSize.Width)
 				return base.MeasureOverride(availableSize);
 

src/Core/src/Platform/Windows/MauiNavigationView.cs

@@ -124,6 +124,10 @@ protected override void OnApplyTemplate()
 			// It causes the content to not be flush up against the title bar
 			PaneContentGrid.Margin = new WThickness(0, 0, 0, 0);
 			UpdateMenuItemsContainerHeight();
+
+			// On WinAppSDK 1.7, it seems that if the PaneContentGrid width is not explicitly set,
+			// it takes on the desired width of its child.
+			PaneContentGrid.Width = OpenPaneLength;
 		}
 
 

src/Core/src/Platform/Windows/NavigationViewExtensions.cs

@@ -249,9 +249,19 @@ public static void UpdateFlyoutBehavior(this MauiNavigationView navigationView,
 		public static void UpdateFlyoutWidth(this MauiNavigationView navigationView, IFlyoutView flyoutView)
 		{
 			if (flyoutView.FlyoutWidth >= 0)
+			{
 				navigationView.OpenPaneLength = flyoutView.FlyoutWidth;
+			}
 			else
+			{
 				navigationView.OpenPaneLength = 320;
+			}
+
+			if (navigationView.PaneContentGrid is not null)
+			{
+				navigationView.PaneContentGrid.Width = navigationView.OpenPaneLength;
+			}
+
 			// At some point this Template Setting is going to show up with a bump to winui
 			//handler.PlatformView.OpenPaneLength = handler.PlatformView.TemplateSettings.OpenPaneWidth;
 		}