How do I load images in the background?

Question

I am trying to load an image in the background and then update the UI. I have been playing with this all day and I don\'t know what I am missing. I keep getting the follow

Answer 1

Your code to load the image (.jpg) into memory should be done in the background. Code to load the image from memory into a WPF control must be done in the normal UI WPF thread. Only slow/long running tasks should be put into a background thread. Once the long task is complete, it must signal the UI thread to update the view with the result of the long task.

My favourite way is using the BackgroundWorker class:

var bg = new System.ComponentModel.BackgroundWorker();
bg.DoWork += Work_Function;
bg.RunWorkerCompleted += UI_Function;
bg.RunWorkerAsync();

void Work_Function(object sender, DoWorkEventArgs e) { ... }
void UI_Function(object sender, RunWorkerCompletedEventArgs e) { ... }

When you call RunWorkerAsync(), first your Work_Function() is called. When it is complete, the UI_Function() is called. The work function may place one variable in the DoWorkEventArgs.Result property, which is accessible from the RunWorkerCompletedEventArgs.Result property.

I think you might also be interested in this article: http://www.codeproject.com/KB/WPF/WPF_Explorer_Tree.aspx It shows how to set up Lazy Loading in a tree view in WPF. I think the basic concept (add a dummy node, intercept the display of the dummy node by loading the next image instead) will apply to your work.