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Editorial Team
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Asked: 2026-05-15T03:28:04+00:00

I’m familiar with the following: If the operation raises an exception that your code

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I’m familiar with the following:

“If the operation raises an exception that your code does not handle, the BackgroundWorker catches the exception and passes it into the RunWorkerCompleted event handler, where it is exposed as the Error property of System.ComponentModel.RunWorkerCompletedEventArgs. If you are running under the Visual Studio debugger, the debugger will break at the point in the DoWork event handler where the unhandled exception was raised.”

However, I’ve encountered a weird glitch.

In my component, there’s an instance of BackgroundWorker.

Even though it’s not running in the debugger, the exception remains unhandled by the worker.

Even simplified code produces an unhandled exception (and RunWorkerCompleted doesn’t fire):

Throw New ArgumentException("Test")

The main thing is the code of RunWorkerComplete:

RaiseEvent UpdateComplete(Me, New AsyncCompletedEventArgs(e.Error, e.Cancelled, e.Result))

I need the component to expose the worker exception through a public event.

If I remove the RaiseEvent call, the exception becomes handled by the worker, and accessible through e.Error.

Apparently, raising an event causes the worker to miss the exception. How can that be?

Full Code:

Component:

Private Sub workerDownloader_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs)

        RaiseEvent UpdateComplete(Me, New AsyncCompletedEventArgs(e.Error, e.Cancelled, e.Result))

End Sub

Private Sub workerDownloader_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs)
        Throw New ArgumentException("Test")
End Sub

Host app (WinForms):

Private Sub Connector1_UpdateComplete(ByVal sender As System.Object, ByVal e As System.ComponentModel.AsyncCompletedEventArgs) Handles Connector1.UpdateComplete
        If e.Error IsNot Nothing Then MessageBox.Show(e.Error.ToString)
End Sub
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1 Answer

  1. Editorial Team

    Update based on your updates to the question…
    I’ve mocked this up in C# code and it looks like it’s a (cross thread?) issue trying to pass the Result from the event args to the AsyncCompletedEventArgs.

    Passing the error and the cancel works, but when I try to pass the result object, it dies. Do you need the result object in the event?

    UpdateComplete(this, new AsyncCompletedEventArgs(e.Error, e.Cancelled, null));
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