I'm getting an error even when I wrap it in Dispatcher.BeginInvoke

Question

In c# I'm trying to fade a Image in then out in my application. Its a image in the MainPage. At first it works great. But If I navigate to another site, lets say Settings.xaml and then back to MainPage the Dispatcher throws Invalid cross-thread access.

Anyone got an idea, this is how I'm trying to set the images opacity in my BackgroundWorker's _DoWork function:

Dispatcher.BeginInvoke(() =>
                    {
                        MyImage.Opacity = opacity;
                    });

Funny, it does not break, but put a breakpoint on it and it says everything is Invalid cross-thread access.

you use the OnProgressChanged event to update the UI. See here: http://stackoverflow.com/questions/1862590/how-to-update-gui-with-backgroundworker — Ric, Jan 12 '13 at 17:33
Just for completeness, you know that you can animate a control's `Opacity` by a `DoubleAnimation` in a `Storyboard`? — Clemens, Jan 12 '13 at 18:04

Alexander Balte · Accepted Answer · 2013-01-12T18:25:27.843

1

Try to implement your fading logic using Animation, not BackgroundWorker. It may help.

Have you tried this way?

Another way using Windows Phone Toolkit:

WP7 Transitions in depth | key concepts and API

WP7 Transitions in depth | custom transitions

It's old articles, but they may contain usefull information.

edited Jan 12 '13 at 18:25

answered Jan 12 '13 at 18:05

Alexander Balte

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gleb.kudr · Answer 2 · 2013-01-13T14:21:11.087

Try this:

Dispatcher.Invoke(DispatcherPriority.ContextIdle, new Action(delegate()
        {
            //your code in another thread you want to invoke in UI thread
        }));

You should invoke it from the UI thread, for example from MainWindow. From my project:

//Event raised on ImageSource property changed while Backgroundwoker in MainWindow class:
    void binding_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        MyProject.ImageCropSize crop = MyProject.ImageCropSize.SourceCrop;

        this.Dispatcher.Invoke(DispatcherPriority.ContextIdle, new Action(delegate()
        {
            BitmapImage bmisource = image1.Source as BitmapImage;
            bmisource = null;//new BitmapImage();
            GC.Collect();

            BitmapImage bmi = MyProject.ImageData.ConvertFromBitmapToBitmapImage(((ImageBinding)sender).BitMap, crop);
            image1.Source = bmi;
            ((ImageBinding)sender).Clear();

        }));
    }

I'm getting an error even when I wrap it in Dispatcher.BeginInvoke

2 Answers2