Clear PopupFlyout target on flyout close

[BAndysc]

What does the pull request do?

Flyouts hold a strong reference to target object: #15465 leaking memory. Luckily when the same menu is opened on another target, the memory is released. Still, this is a bug.

What is the current behavior?

What is the updated/expected behavior with this PR?

How was the solution implemented (if it's not obvious)?

The Target in PopupFlyoutBase will be cleared on popup close. I am not sure if this changes any behaviour or not.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Not sure if this changes flyouts behaviour or not.

Obsoletions / Deprecations

Fixed issues

Fixes #15465

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047560-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047568-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[robloo]

I don't think you can do this. Target is a valid property and is required for positioning the popup. If you clear it after flyout closes, how will it position correctly the next time it opens?

[BAndysc]

Keep in mind Target != PlacementTarget. As far as I can see, not sure tho, Target (outside of PopupFlyoutBase) is used only in button:

https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Controls/Button.cs#L675-L692

and this usage is still valid, because in the event Target is already set.

usages of Target property

[robloo]

So we have a different issue here too. Target is from UWP Flyouts and PlacementTarget is from WPF Popups. We really shouldn't have both and one needs to be obsoleted.

Both properties should really behave the same too. (Havnt looked at code to see how PlacementTarget handles this).

[maxkatz6]

@robloo it's a bit simpler here. Flyout doesn't have PlacementTarget property. It's an argument of ShowAt(placementTarget) method. And Target property is only set while Flyout is shown, IIRC it's the same in UWP.

[maxkatz6]

Double checked, WinUI behaves this way as I expected:

Opening: Microsoft.UI.Xaml.Controls.Button
Opened: Microsoft.UI.Xaml.Controls.Button
Closing: Microsoft.UI.Xaml.Controls.Button
Closed: Microsoft.UI.Xaml.Controls.Button
After Closed: (null) # used a DispatcherQueue

On a Button with ContextFlyout

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0047580-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]