Form UI Freeezes even after using Backgroundworker when using Flickr.Net API

Question

Im trying to upload some images using the Flickr.net API.The Images are uploaded but the User Interface freezes.I have inserted the code for uploading in a Background worker

Answer 1

If you are doing something like:

while(worker.IsBusy)
{
}

to wait for it to finish, this will hang because it ties up the UI thread in the loop and since the background worker needs to invoke onto the UI thread to set the busy property safely there is a dead lock.

Answer 2

Two common causes for this, your snippet is way too brief to narrow down which it might be. First is the ReportProgress method, the event handler runs on the UI thread. If you call it too often then the UI thread can get flooded with invoke requests and spend too much time to handle them. It doesn't get around to doing its regular duties anymore, like responding to paint requests and processing user input. Because as soon as it is done handling a invoke request, there's another one waiting to get dispatched. The UI thread isn't actually frozen, it just looks like it is. The net effect is the same. You'll need to fix it by slowing down the worker or call ReportProgress less often.

The second cause is your flicker object not being thread-safe and itself ensuring that it is used in a thread-safe way. By marshaling the call from the worker thread to the UI thread automatically. This is very common for COM components, this kind of marshaling is a core feature of COM. Again the UI thread isn't actually frozen, but it still won't handle paint and input since it is busy uploading a photo. You'll need to fix it by creating the flicker object on the worker thread. With good odds that you can't do this with a BackgroundWorker, such a component often needs an STA thread that pumps a message loop. Which requires Thread.SetApartmentState() and Application.Run().