Exception in DataContextChanged event

Question

Exception in DataContextChanged event

Rousselle, Holger 1

If there is an exception in the DataContextChanged event, the exception will stop displaying the MainPage, but the app is still running.
The same behavior when an exception is thrown in the DataContextChanged event of controls on the MainPage.
The exception can't be catched when adding UnhandledException += OnUnhandledException; in the App.cs

Added a small blank UWP app where an exception is thrown in the DataContextChanged of the MainPage.

https://drive.google.com/file/d/1yNJM9p2RdD06Z115vvnYyTYU_R8K6BN8/view?usp=sharing

Yan Gu - MSFT 2,676 Reputation points

2021-03-11T09:10:47.72+00:00

@Rousselle, Holger I have reproduced the problem as you mentioned by using your sample. The OnUnhandledException event handler isn’t called when an exception is throw in DataContextChanged event handler. I need to consult other engineers. There may be some delays.
Rousselle, Holger 1 Reputation point

2021-04-06T17:08:18.45+00:00

Any updates on this topic?
Yan Gu - MSFT 2,676 Reputation points

2021-04-07T02:00:07.647+00:00

@Rousselle, Holger We are waiting for the response from other engineers. I will notify you as soon as there is new information about the case.
Anthony Soto 81 Reputation points

2021-05-04T00:39:52.08+00:00
Hello @Rousselle, Holger ,

I have looked into the issue behavior you describe, and can repro it myself, too. If possible, could you provide further explanation on how this issue is causing problems with your project specifically? Are exceptions commonly being thrown in this event callback with your project?

From testing with your sample, I notice that my Page UI does still manage to generate, but any UI element bindings are not updated properly if the DataContext is changed by, for example, a button click.

If you wrap the thrown exception inside of a Dispatcher.RunAsync call and dispatch it to the main thread, you see the expected behavior of App.UnhandledException being triggered and the app terminating. It is odd behavior, but this could be possibly due to some internal wrapping going on with OnDataContextChanged.

await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { throw new NullReferenceException(); });

Your answer

Yan Gu - MSFT 2,676 Reputation points

2021-03-11T09:10:47.72+00:00

@Rousselle, Holger I have reproduced the problem as you mentioned by using your sample. The OnUnhandledException event handler isn’t called when an exception is throw in DataContextChanged event handler. I need to consult other engineers. There may be some delays.
Rousselle, Holger 1 Reputation point

2021-04-06T17:08:18.45+00:00

Any updates on this topic?
Yan Gu - MSFT 2,676 Reputation points

2021-04-07T02:00:07.647+00:00

@Rousselle, Holger We are waiting for the response from other engineers. I will notify you as soon as there is new information about the case.
Anthony Soto 81 Reputation points

2021-05-04T00:39:52.08+00:00

Hello @Rousselle, Holger ,

I have looked into the issue behavior you describe, and can repro it myself, too. If possible, could you provide further explanation on how this issue is causing problems with your project specifically? Are exceptions commonly being thrown in this event callback with your project?

From testing with your sample, I notice that my Page UI does still manage to generate, but any UI element bindings are not updated properly if the DataContext is changed by, for example, a button click.

If you wrap the thrown exception inside of a Dispatcher.RunAsync call and dispatch it to the main thread, you see the expected behavior of App.UnhandledException being triggered and the app terminating. It is odd behavior, but this could be possibly due to some internal wrapping going on with OnDataContextChanged.

await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { throw new NullReferenceException(); });

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Exception in DataContextChanged event

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