NullReferenceException on ToolTipChanged on Windows 10

Describe the bug

I’m developing on Windows 11 and test my app on Windows 10 21H2. Everything works fine on Windows 11. However on Windows, my app crashes when I pass the mouse on the icon in the system tray.

Message:

Object reference not set to an instance of an object.

Call stack:

   at WinRT.ExceptionHelpers.<ThrowExceptionForHR>g__Throw|20_0(Int32 hr)
   at H.NotifyIcon.TaskbarIcon.OnToolTipChange(Object sender, Boolean visible)
   at H.NotifyIcon.Core.MessageWindow.ProcessWindowMessage(UInt32 msg, WPARAM wParam, LPARAM lParam)
   at H.NotifyIcon.Core.MessageWindow.OnWindowMessageReceived(HWND hWnd, UInt32 msg, WPARAM wParam, LPARAM lParam)

Steps to reproduce the bug

1. Be on Windows 10 build 19044.2075 (21H2) (does not reproduce on Windows 11)
2. Using H.NotifyIcon.WinUI 2.0.68` and above.
3. Create a windowless WinUI 3 app using this sample: https://github.com/HavenDV/H.NotifyIcon/tree/master/src/apps/H.NotifyIcon.Apps.WinUI.Windowless
4. Update WinAppSDK to 1.2.220930.4-preview2 (I admit I didn’t try with an older version)
5. Have a XAML similar to

<tb:TaskbarIcon
        x:Key="NotifyIcon"
        Visibility="Visible"
        ToolTipText="MyTooltip"
        ContextMenuMode="SecondWindow">
        [...]
    </tb:TaskbarIcon>

1. Start the app from Visual Studio 2022
2. Pass the mouse above the icon in the systray, without clicking.
3. NRE exception gets raised and don’t seem to be handled.
4. App end up crashing 😃

Expected behavior

No crash 😃 Tooltip should appear.

Screenshots

No response

NuGet package version

2.0.68 Also tried with 2.0.73

Platform

WinUI

IDE

Visual Studio 2022

Windows Version

Windows 10

WindowsAppSDK Version

Other

WindowsAppSDK Type

Packaged

Manifest

No response

Additional context

Windows 10 build 19044.2075 (21H2)

[justinsoderstrom]

I can see something similar happening on my system (also Windows 10) with the WinUI.Windowless example project. However in my case the null reference exception is thrown as soon as it reaches line 231 in TaskBarIcon.ToolTips.cs. This line causes issues:

TrayToolTipResolved.IsOpen = true;

While debugging I can see TrayToolTipResolved is defined so maybe the error is somewhere deeper in the IsOpen setter? The stack trace I get

   at WinRT.ExceptionHelpers.<ThrowExceptionForHR>g__Throw|20_0(Int32 hr)
   at ABI.Microsoft.UI.Xaml.Controls.IToolTipMethods.set_IsOpen(IObjectReference _obj, Boolean value)  
   at H.NotifyIcon.TaskbarIcon.OnToolTipChange(Object sender, Boolean visible) in C:\\Projects\\H.NotifyIcon\\src\\libs\\H.NotifyIcon.Shared\\TaskbarIcon.ToolTips.cs:line 231"

I added a trivial check to WinUI to bypass this area. Please check 74 version on NuGet. But I’m guessing the problem is deeper, it’s just a temporary solution to bypass NRE.

NRE no longer occurs for me on 74 version.

[HavenDV]

I can see something similar happening on my system (also Windows 10) with the WinUI.Windowless example project. However in my case the null reference exception is thrown as soon as it reaches line 231 in TaskBarIcon.ToolTips.cs.

This line causes issues:

TrayToolTipResolved.IsOpen = true;

While debugging I can see TrayToolTipResolved is defined so maybe the error is somewhere deeper in the IsOpen setter?

The stack trace I get

   at WinRT.ExceptionHelpers.<ThrowExceptionForHR>g__Throw|20_0(Int32 hr)
   at ABI.Microsoft.UI.Xaml.Controls.IToolTipMethods.set_IsOpen(IObjectReference _obj, Boolean value)  
   at H.NotifyIcon.TaskbarIcon.OnToolTipChange(Object sender, Boolean visible) in C:\\Projects\\H.NotifyIcon\\src\\libs\\H.NotifyIcon.Shared\\TaskbarIcon.ToolTips.cs:line 231"

I added a trivial check to WinUI to bypass this area. Please check 74 version on NuGet. But I’m guessing the problem is deeper, it’s just a temporary solution to bypass NRE.