Question

I need to update a C# WinForms PictureBox from a MemoryStream input.
I was able to accomplish this using

pictureBox.Image = new Bitmap(new MemoryStream(payload));

in the thread that parses the stream [RxThread()] but was advised to use a delegate to avoid undesirable effects.
So I’ve implemented this:

private void RxThread()
{
    ...
    var imageDelegateClass = new ImageDelegateClass();
    var imageDelegate = new ImageDelegate(imageDelegateClass.SetImage);
    imageDelegate(payload);
    ...
}

delegate void ImageDelegate(byte[] payload);
class ImageDelegateClass
{
    public void SetImage(byte[] payload)
    {
        pictureBox.Image = new Bitmap(new MemoryStream(payload));
    }
}

but get the following error code when I try to compile:

Cannot access a non-static member of
outer type ‘FormMain’ via nested type
‘FormMain.ImageDelegateClass’

I am sure its a bad idea to make pictureBox static since it is WinForms generated.
I know the repair is probably simple but I am a bit new to C#.
I have read the chapter on Delegates in Jon Skeets C# In Depth 2nd Edition multiple times but this is the first time I’ve actually tried to use one.
How can I change SetImage() so it can access pictureBox?

Answer 1

You should move the method to the form class itself.
You don’t need a separate class at all.

Also, you can use the built-in Action<byte[]> delegate instead of creating your own delegate type.

Also, just calling the the delegate directly doesn’t do you any good; it will still run on the background thread.

You need to call BeginInvoke(new Action<byte[]>(this.SetImage), payload) to run the delegate on the UI thread.