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POWPF and backgroundworker problem
 

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  1. POWPF and backgroundworker problem
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    <p>In my program there is a BackgroundWorker class that preloads the images to BitmapImage object. I need to pass that preloaded image to the main application(WPF), where it will be copied to another BitmapImage object. This seems to be working, however, when i try</p> <pre><code>imgViewer.Source = imgNext; //imgNext is a main app copy of the preloaded image </code></pre> <p>an error occurs meaning that that object(imgNext) is owned by another thread and it cannot be used.</p> <p>Any ideas how to get rid of it and get the code working? </p> <p>Thanks everybody for answering!</p> <p>In fact, I managed to solve this problem by creating a static <code>BitmapImage</code> inside <code>App</code> class. Before using it, I do</p> <pre><code> App.iNext = null; </code></pre> <p>Then I load the actual image and freeze it, so this static property can be accessed from everywhere. When the cycle repeats many times, assigning null prevents 'object is frozen' errors.</p> <p>And of course, there was a lot of work with managing single BGW instance, queuing tasks etc.</p> <p><em>(Currently I'm using ImagesContainer class defined also in my program that has two BitmapImage properties. I use it to receive preloaded images from backgroundworker. )</em></p> <p><em>imgNext is a public variable defined in MainWindow. (main thread)</em></p> <pre><code> void bwImgLoader_DoWork(object sender, DoWorkEventArgs e) { backgrLoadNextPrevList list = e.Argument as backgrLoadNextPrevList; ImagesContainer result = new ImagesContainer(); if (list.HasNextPath) result.imgPrev = PrepareImage(list.NextPath); if (list.HasPrevPath) result.imgNext = PrepareImage(list.PrevPath); e.Result = result; } void bwImgLoader_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { ImagesContainer result = e.Result as ImagesContainer; if (result.imgNext != null) { setNextDelegate s = new setNextDelegate(setNext); object[] t = { result.imgNext }; imgNext.Dispatcher.Invoke(s, t); } // do not take into account this line, just ignore it. //if (result.imgPrev != null) imgPrev = result.imgPrev; } public void setNext(BitmapImage b) { imgNext = b; } public delegate void setNextDelegate(BitmapImage b); </code></pre> <p>Freezing the bitmapimage helps only on the first background load(see the comment under the answer below). When I call BackgroundWorker second time, an errors occures that the object is frozen and cannot be modified. Is there a way to un-freeze it?</p> <p>Or, is there any way to copy data from one thread to another without copying an attribution to thread?</p> <hr> <hr> <p><strong>UPDATED</strong></p> <p>Thanks everybody for answering!</p> <p>In fact, I managed to solve this problem by creating a static <code>BitmapImage</code> inside <code>App</code> class. Before using it, I do</p> <pre><code> App.iNext = null; </code></pre> <p>Then I load the actual image and freeze it, so this static property can be accessed from everywhere. When the cycle repeats many times, assigning null prevents errors.</p> <p>And of course, there was a lot of work with managing single BGW instance, queuing tasks etc.</p> <p>But these efforts were worth the result - I got +125% in performance!!! Thank everyone!</p>
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    1. USsimon
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    1. COYou have an empty `catch { }` block in there.
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      1. USHenk Holterman
    2. COduplicate? http://stackoverflow.com/questions/532740/wpf-how-to-handle-errors-with-a-backgroundworker
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    3. CO@ Will Hughes : that doesn't help. I need to assing a source for ui element that is owned by another thread
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