[windows] fix memory leak in WebView
#18810
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Context: dotnet#18365 Context: https://github.com/heyThorsten/GCTest Testing the sample app, I could see a leak in `WebView` on Windows. A memory snapshot showed: Microsoft.Maui.Handlers.WebViewHandler Windows.Foundation.TypedEventHandler<Microsoft.UI.Xaml.Controls.WebView2, Microsoft.UI.Xaml.Controls.CoreWebView2InitializedEventArgs> WinRT._EventSource_global__Windows_Foundation_TypedEventHandler_global__Microsoft_UI_Xaml_Controls_WebView2__global__Microsoft_UI_Xaml_Controls_CoreWebView2InitializedEventArgs_+EventState Windows.Foundation.TypedEventHandler<Microsoft.UI.Xaml.Controls.WebView2, Microsoft.UI.Xaml.Controls.CoreWebView2InitializedEventArgs> [Dependent Handle, Microsoft.Maui.Platform.LayoutPanel <0x2079E7A8D00>] Microsoft.UI.Xaml.RoutedEventHandler WinRT._EventSource_global__Microsoft_UI_Xaml_RoutedEventHandler+EventState Microsoft.UI.Xaml.RoutedEventHandler [Dependent Handle, Microsoft.Maui.Platform.LayoutPanel <0x2079E7A8D00>] I could this same leak in `WebView` by updating `MemoryTests` to do: if (view is WebView webView) { webView.Source = new HtmlWebViewSource { Html = "<p>hi</p>" }; await Task.Delay(1000); } After a bit of debugging, I found that events on `WebView` seem to suffer from the same "circular reference" problem we see on iOS. This makes sense, as it is an unmanaged/native control. (Might be COM?) So we have the cycle: * `WebViewHandler` -> * `WebView2` -> * Various `WebView2` events: * `CoreWebView2Initialized` * `HistoryChanged` * `NavigationStarting` * `NavigationCompleted` * `WebViewHandler` Using the same pattern we've been using for iOS: creating a `WebView2Proxy` type solves the issue. Note that I didn't have to do this for all events, just the ones subscribing to `WebView2`-related events. I also don't see the `WebView2Proxy` object living forever, so the issue does appear to be a cycle.
jonathanpeppers
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Eilon
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rmarinho
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Nov 17, 2023
| @@ -25,7 +26,7 @@ internal WebNavigationEvent CurrentNavigationEvent | |||
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| protected override void ConnectHandler(WebView2 platformView) | |||
| { | |||
| platformView.CoreWebView2Initialized += OnCoreWebView2Initialized; | |||
| _proxy.Connect(this, platformView); | |||
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Hum shouldn't we just connect the proxy when WebView2 is initialized? I think we need this I remember other bug related with this where there was an exception related with this. @Eilon do you remember ?
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The connect method should be the same as what it was doing before:
public void Connect(WebViewHandler handler, WebView2 platformView)
{
_handler = new(handler);
platformView.CoreWebView2Initialized += OnCoreWebView2Initialized;
}I don't think I changed any events -- just moved methods to a new class.
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@rmarinho hmm sorry I don't specifically remember a bug around this, but maybe there was.
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Nov 17, 2023
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Context: #18365
Context: https://github.com/heyThorsten/GCTest
Testing the sample app, I could see a leak in
WebViewon Windows. A memory snapshot showed:I could this same leak in
WebViewby updatingMemoryTeststo do:After a bit of debugging, I found that events on
WebViewseem to suffer from the same "circular reference" problem we see on iOS. This makes sense, as it is an unmanaged/native control. (Might be COM?)So we have the cycle:
WebViewHandler->WebView2->WebView2events:CoreWebView2InitializedHistoryChangedNavigationStartingNavigationCompletedWebViewHandlerUsing the same pattern we've been using for iOS: creating a
WebView2Proxytype solves the issue. Note that I didn't have to do this for all events, just the ones subscribing toWebView2-related events. I also don't see theWebView2Proxyobject living forever, so the issue does appear to be a cycle.