[ios] fix memory leak in Frame, VisualElementRenderer
#18552
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Context: dotnet#18365 I could reproduce a leak in `Frame` by adding a parameterized test: [InlineData(typeof(Frame))] public async Task HandlerDoesNotLeak(Type type) `FrameRenderer` has a circular reference via its base type, `VisualElementRenderer`: * `Frame` -> * `FrameRenderer` / `VisualElementRenderer` -> * `Frame` (via `VisualElementRenderer._virtualView`) To solve this issue, I made `_virtualView` a `WeakReference`, but only on iOS or MacCatalyst platforms. We don't necessarily need this treatment for Windows or Android. My initial attempt threw a `NullReferenceException`, because the `Element` property is accessed before `SetVirtualView()` returns. I had to create a `_tempElement` field to hold the value temporarily, clearing it to avoid a circular reference. The Roslyn analyzer didn't catch this cycle because it doesn't warn about `IPlatformViewHandler`, only `NSObject`'s. Will investigate further on this example here: jonathanpeppers/memory-analyzers#12
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Context: #18365
I could reproduce a leak in
Frameby adding a parameterized test:FrameRendererhas a circular reference via its base type,VisualElementRenderer:Frame->FrameRenderer/VisualElementRenderer->Frame(viaVisualElementRenderer._virtualView)To solve this issue, I made
_virtualViewaWeakReference, but only on iOS or MacCatalyst platforms. We don't necessarily need this treatment for Windows or Android.My initial attempt threw a
NullReferenceException, because theElementproperty is accessed beforeSetVirtualView()returns. I had to create a_tempElementfield to hold the value temporarily, clearing it to avoid a circular reference.The Roslyn analyzer didn't catch this cycle because it doesn't warn about
IPlatformViewHandler, onlyNSObject's. Will investigate further on this example here:jonathanpeppers/memory-analyzers#12