WPF custom BalloonTips problem with multithreading

0 votes
asked Apr 1, 2010 by erika

I have read other related question but i cant really get them to relate to this so I thought it were best to ask, Im pretty new to WPF and so on so please bear with me.

I am using this http://www.codeproject.com/KB/WPF/wpf_notifyicon.aspx api to work with custom WPF Windows (in particular FancyBalloon).

However, i'm coming across the following problem, I seem unable to start off BalloonTips in a separate thread ( i need this because i'm parsing emails and hence if there are 3 emails for instance, it displays the first email (that works fine), but when it comes to the second email it crashes with a TargetInvocationException , {"Specified element is already the logical child of another element. Disconnect it first."}.

Thing is, im supposedly working with the same instance and i have attempted calling it to close it before, disposing it etc but to no avail. (then again if i dispose it, i cant create another instance as apparently WPF UI components must be called from a static thread so throughout the looping of emails + displaying balloon, i am trying to use the same BalloonTip.

Any suggestions please? I am really at a loss here and i've been on it for quite a while now :/

I was wondering if there was anyone

2 Answers

+1 vote
answered Apr 1, 2010 by alex

It seems you are adding the same UI element to multiple parent containers at the same time.

For example, if I attempt myStackPanel.Children.Add(myUIElement) concurrently in separate threads, referring to the same UI element object, this would cause the error you are seeing.

If you need the same UI elements for multiple threads, consider cloning them or moving your UI logic to the main thread.

+2 votes
answered Apr 1, 2010 by dthorpe

In general, WPF controls should be accessed and updated only on the main UI thread. There are thread affinity checks all over the data binding innards that will throw an exception if you assign to a data bound property from any thread that isn't the WPF UI thread, for example.

You can either remove the UI code from your background worker thread, or make judicious use of a SynchronizationContext to invoke from your background thread snippets of code to execute on the UI thread.

If you're new to WPF or new to threading, you should keep the UI stuff out of the background threads. WPF has plenty of complexity to keep you busy without adding the additional headache of threading issues to the mix.

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