Fix InAppNotification not working show/hide/show sequence

[vgromfeld]

Fixes #3451

When using InAppNotification and running the Show()/Dismiss()/Show() sequence "too fast", we never see the last notification.

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

When running the following code in the InAppNotification sample page, we are not seeing the last notification:

 SampleController.Current.RegisterNewCommand("Show hide show", (sender, args) =>
 {
      _exampleInAppNotification?.Show("Notification 1", 0);
      _exampleInAppNotification?.Dismiss();
      _exampleInAppNotification?.Show("Notification 2", 0);
});

What is the new behavior?

The InAppNotification content visibility is driven by two VisualStates and the control visibility is controlled using its Visibility property.

When going "too fast", we have the following sequence:

• show notification 1 is called
  -- control visibility set to visible
  -- request visual state change to "visible"
• dismiss is called
  -- request visual state change to "hidden"
• show notification 2 is called
  -- request visual state change to "visible"
  -- visual state changed to "visible"
  -- visual state changed to "hidden"
  -- control visibility set to collapsed (See OnNotificationCollapsed())
  -- visual state changed to "visible"

The visual states changed events are raised even if we've never really gone into the state and our event handler for the "hidden" state is forcing the control to be collapsed.
Forcing the control to be displayed when entering the visible state is ensuring that the control visibility remains synchronized with its content.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

[ghost]

Thanks vgromfeld for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[Kyaa-dost]

"D:\a\1\s\Windows Community Toolkit.sln" (Build target) (1) ->
"D:\a\1\s\Microsoft.Toolkit.Uwp.UI.Controls\Microsoft.Toolkit.Uwp.UI.Controls.csproj" (default target) (9:2) ->
(CoreCompile target) ->
InAppNotification\InAppNotification.cs(72,80): error SA1028: Code should not contain trailing whitespace [D:\a\1\s\Microsoft.Toolkit.Uwp.UI.Controls\Microsoft.Toolkit.Uwp.UI.Controls.csproj]

@vgromfeld Seeing this error regarding build failure

[Sergio0694]

Looks great, good catch @vgromfeld! 🚀