Can't set ProtectedCursor in DependencyProperty PropertyChangedCallback - Access Violation

[michael-hawker]

Describe the bug

Tested on both latest 1.1.0-preview3 (not an option in dropdown below) and 1.0.1,

I'm hitting a 0xC0000005: Access violation reading location 0x0000000000000000. error when trying to set the ProtectedCursor on my derived control. I'm trying to update our new refactor of GridSplitter and related controls in the Toolkit to work with WinUI 3 from this PR here CommunityToolkit/WindowsCommunityToolkit#4083 (related to issue #4509 here as well).

We'd like to showcase this component in our new Labs setup. Seems more severe of an issue than previously reported #6058.

Interesting to note is that if I change this value within OnApplyTemplate it seems to work fine. However, when being called as a result of the XAML DependencyProperty PropertyChangedCallback - updating it fails with this error.

I tried to use a DispatcherQueue within the callback, but that resulted in the same error. (Even though this should already be still on the UI thread, so I wouldn't expect to have to do this here.)

Steps to reproduce the bug

Derive a control and try and set the ProtectedCursor property:

ProtectedCursor = InputSystemCursor.Create(InputSystemCursorShape.SizeNorthSouth);

Move this to a DependencyPropertyChanged callback, see error.

Happy to add someone to our repo and point them to the commit where we can reproduce this in Labs.

Expected behavior

Should not crash and set the cursor to the specified value.

Screenshots

No response

NuGet package version

WinUI 3 - Windows App SDK 1.1 Preview 2: 1.1.0-preview3

Windows app type

• UWP
• Win32

Device form factor

Desktop

Windows version

Windows 10 (21H2): Build 19044

Additional context

Exception thrown at 0x00007FFDB995F223 (Microsoft.ui.xaml.dll) in SizerBase.WinAppSdk.exe: 0xC0000005: Access violation reading location 0x0000000000000000.
 	Microsoft.ui.xaml.dll!CInputServices::SetCursor()	Unknown
 	Microsoft.ui.xaml.dll!CInputServices::UpdateCursor()	Unknown
 	Microsoft.ui.xaml.dll!CUIElement::SetValue()	Unknown
 	Microsoft.ui.xaml.dll!CFrameworkElement::SetValue()	Unknown
 	Microsoft.ui.xaml.dll!CControl::SetValue()	Unknown
 	Microsoft.ui.xaml.dll!DirectUI::DependencyObject::SetValueCore()	Unknown
 	Microsoft.ui.xaml.dll!DirectUI::DependencyObject::SetValueByKnownIndex()	Unknown
 	[Managed to Native Transition]	
 	Microsoft.WinUI.dll!ABI.Microsoft.UI.Xaml.IUIElementProtectedMethods.set_ProtectedCursor(WinRT.IObjectReference _obj, Microsoft.UI.Input.InputCursor value)	Unknown
 	Microsoft.WinUI.dll!Microsoft.UI.Xaml.UIElement.ProtectedCursor.set(Microsoft.UI.Input.InputCursor value)	Unknown
>	CommunityToolkit.Labs.WinUI.SizerBase.dll!CommunityToolkit.Labs.WinUI.SizerBase.OnOrientationPropertyChanged(Microsoft.UI.Xaml.DependencyObject d, Microsoft.UI.Xaml.DependencyPropertyChangedEventArgs e) Line 111	C#
 	Microsoft.WinUI.dll!ABI.Microsoft.UI.Xaml.PropertyChangedCallback.Do_Abi_Invoke(System.IntPtr thisPtr, System.IntPtr d, System.IntPtr e)	Unknown
 	[Native to Managed Transition]	
 	Microsoft.ui.xaml.dll!DirectUI::DependencyObject::NotifyPropertyChanged()	Unknown
 	Microsoft.ui.xaml.dll!CDependencyObject::NotifyPropertyChanged()	Unknown
 	Microsoft.ui.xaml.dll!CDependencyObject::SetEffectiveValue()	Unknown
 	Microsoft.ui.xaml.dll!CDependencyObject::UpdateEffectiveValue()	Unknown
 	Microsoft.ui.xaml.dll!CDependencyObject::SetValue()	Unknown
 	Microsoft.ui.xaml.dll!CUIElement::SetValue()	Unknown
...

Working stack:

>	CommunityToolkit.Labs.WinUI.SizerBase.dll!CommunityToolkit.Labs.WinUI.SizerBase.OnOrientationPropertyChanged(Microsoft.UI.Xaml.DependencyObject d, Microsoft.UI.Xaml.DependencyPropertyChangedEventArgs e) Line 111	C#
 	CommunityToolkit.Labs.WinUI.SizerBase.dll!CommunityToolkit.Labs.WinUI.SizerBase.OnApplyTemplate() Line 124	C#
 	Microsoft.WinUI.dll!Microsoft.UI.Xaml.FrameworkElement.Microsoft.UI.Xaml.IFrameworkElementOverrides.OnApplyTemplate()	Unknown
 	Microsoft.WinUI.dll!ABI.Microsoft.UI.Xaml.IFrameworkElementOverrides.Do_Abi_OnApplyTemplate_2(System.IntPtr thisPtr)	Unknown
 	[Native to Managed Transition]	
 	Microsoft.ui.xaml.dll!DirectUI::FrameworkElementGenerated::OnApplyTemplateProtected()	Unknown
 	Microsoft.ui.xaml.dll!DirectUI::FrameworkElement::OnApplyTemplateFromCore()	Unknown
 	Microsoft.ui.xaml.dll!CFrameworkElement::InvokeApplyTemplate()	Unknown
 	Microsoft.ui.xaml.dll!CFrameworkElement::MeasureCore()	Unknown
 	Microsoft.ui.xaml.dll!CUIElement::MeasureInternal()	Unknown
 	Microsoft.ui.xaml.dll!CUIElement::Measure()	Unknown
 	Microsoft.ui.xaml.dll!CGrid::MeasureCell()	Unknown
 	Microsoft.ui.xaml.dll!CGrid::MeasureCellsGroup()	Unknown
 	Microsoft.ui.xaml.dll!CGrid::MeasureOverride()	Unknown
 	Microsoft.ui.xaml.dll!CFrameworkElement::MeasureCore()	Unknown
 	Microsoft.ui.xaml.dll!CUIElement::MeasureInternal()	Unknown
 	Microsoft.ui.xaml.dll!CUIElement::Measure()	Unknown
 	Microsoft.ui.xaml.dll!DirectUI::UIElementGenerated::Measure()	Unknown
 	Microsoft.ui.xaml.dll!DirectUI::Page::MeasureOverride()	Unknown
...

Related microsoft/WindowsAppSDK#1816

[MikeHillberg]

I think the issue is that it can only be called when it's in the live tree, so OnApplyTemplate or the Loaded event handler are workarounds.

[michael-hawker]

@MikeHillberg thanks, If I ignore the first change from the DependencyProperty being set in XAML, I can still grab the value and call to set it in OnApplyTemplate. Will see how that holds up with some more testing and when dynamically changing the property at runtime which is trying to update this.

Opened a doc bug to add a note about this for now.