LiveCharts Navigation Exception on iOS and .NET 9

[jai-io]

Describe the bug
When navigating away from a page containing a LiveChart graph using the back button, the application throws the following casting exception:

System.Exception: Unable to cast to ContentView
   at LiveChartsCore.SkiaSharpView.Maui.ChartBehaviour.<>c__DisplayClass0_0.<On>b__0(Object sender, EventArgs e) in /_/src/skiasharp/LiveChartsCore.SkiaSharpView.Maui/ChartBehaviour.cs:line 58

To Reproduce
Steps to reproduce the behavior:

1. Load a page containing a LiveChart graph
2. Navigate away from the page using the back button

Environment:

• OS: Mac OS 15.1 (24B83)
• iOS Simulator: 18.1
• .NET SDK: 9.0.100
• LiveChartsCore.SkiaSharpView.Maui Nuget Package: 2.0.0-rc4.5

Additional context
While I haven't thoroughly investigated the Android platform, preliminary observations suggest this issue is also present there.

[sharifxu]

i'm experiencing the same issue with 2.0.0-rc2, any workarounds for this?

[xhorack]

The same for me. Exceptionis on all platforms, Win, iOS, Android. On Android there is 'Unable to cast to ContentViewGroup' exception. This happened only after upgrading Microsoft.Maui.Controls to version 9.0.10 from 8 on net9. So i'm not sure if this is addresed to MS or LiveCharts. Also tried latest rc 4.5 of LiveCharts, but behavior is the same. After spending a couple of endless nigths, i have still no workaround.

[jai-io]

Looks like this is due to changes in .NET 9 in the way custom control using handlers are cleaned up: Handler disconnection.

Adding HandlerProperties.DisconnectPolicy="Manual" to the control seems to fix the issue. As an example:

                    <maui:CartesianChart
                        Grid.Column="1"
                        HandlerProperties.DisconnectPolicy="Manual"
                        HeightRequest="52"
                        Margin="-16,0,0,0"
                        Series="{Binding Source={RelativeSource AncestorType={x:Type report:StockReportSummaryViewModel}}, Path=StockSummaryPrices.Series}"
                        XAxes="{Binding Source={RelativeSource AncestorType={x:Type report:StockReportSummaryViewModel}}, Path=StockSummaryPrices.XAxes}"
                        YAxes="{Binding Source={RelativeSource AncestorType={x:Type report:StockReportSummaryViewModel}}, Path=StockSummaryPrices.YAxes}"
                        TooltipPosition="Hidden" />

[xhorack]

Well, you are right, i can confirm on all plaforms everything works fine. Thank you.

[jo-ruch]

This happens on Maui 8 on Windows as well when calling Graph.Handler?.DisconnectHandler().

Maui 8.0.21
net8.0-windows10.0.19041.0
LiveChartsCore.SkiaSharpView.Maui 2.0.0-rc4.5

274|2024-12-09T13:27:35.3479033+00:00|ERROR|1|VesselHomePage|Threw --> System.Exception: Unable to cast to ContentPanel
   at LiveChartsCore.SkiaSharpView.Maui.ChartBehaviour.<>c__DisplayClass0_0.<On>b__0(Object sender, EventArgs e) in /_/src/skiasharp/LiveChartsCore.SkiaSharpView.Maui/ChartBehaviour.cs:line 74
   at Microsoft.Maui.Controls.Element.OnHandlerChangedCore()
   at Microsoft.Maui.Controls.VisualElement.OnHandlerChangedCore()
   at Microsoft.Maui.Controls.View.OnHandlerChangedCore()
   at Microsoft.Maui.Controls.Element.SetHandler(IElementHandler newHandler)
   at Microsoft.Maui.Controls.Element.set_Handler(IElementHandler value)
   at Microsoft.Maui.Controls.VisualElement.Microsoft.Maui.IElement.set_Handler(IElementHandler value)
   at Microsoft.Maui.Handlers.ElementHandler.DisconnectHandler(Object platformView)
   at Microsoft.Maui.Handlers.ElementHandler.Microsoft.Maui.IElementHandler.DisconnectHandler()
   at Slick.Views.Components.TelemetryGraph.OnDestroy()

Project to replicate the issue: https://github.com/jo-ruch/LiveCharts2MauiMemoryLeakDemo/tree/disconnect_handler_exception

[maonaoda]

This might be a problem with the implementation of LiveCharts.
Currently, if HandlerProperties.DisconnectPolicy="Manual" is not added, Maui will automatically Disconnect.
At this time, the HandlerChanged event set in ChartBehaviour will be triggered.
At this time, element.Handler?.PlatformView is already null

            var contentView = (Microsoft.Maui.Platform.ContentView?)element.Handler?.PlatformView
                ?? throw new System.Exception("Unable to cast to ContentView");

[maonaoda]

The correct approach should be to use Handler （ConnectHandler/DisconnectHandler）
instead of HandlerChanged

I'll try to modify this process when I have some free time.

[beto-rodriguez]

I tested and I was able to reproduce on the master branch (v rc-4.5)

The good news is that this was fixed with #1704 by @albyrock87, now the chart uses the ChartViewHandler to connect and disconnect handlers, this is now merged to dev and will be included in the next version of the library.

I think this could also fix #1725