Question

I managed to get a webcam running using Aforge. The code can be found in my answer here.

Now I want to do some computer vision stuff and return back some results to the main form. The threading problem I have is in this part from that code:

void FinalVideo_NewFrame(object sender, NewFrameEventArgs eventArgs)
{ Bitmap video = (Bitmap)eventArgs.Frame.Clone();
  pictureBox1.Image = video;
  // count red colors  
  // not yet written
  TextBox1.text = "demo error";  // >> i like to return a value to the main form
 }

The problem however is it’s doing the video frames in another thread, and now I can’t return answers from that thread to the main form back. I didn’t write the Aforge, I only linked it and made it work on my form.

I can’t change the way how Aforge video works. I mean it was never made to result something back that’s something I like to do. Are there ways to get a result back, like a string text in a textbox. On the main form where this code runs from?

I am able to follow a sample code of threading but this is a bit over my head since I got not much influence on how video acquisition in Aforge was designed.

I have been wondering if raising another thread just to update a textbox might work but I am not that sure and wonder that in the end one would create to many threads, causing to much kernel switching load.

Some additional info: the code thread above is started with this button function below.

private void button1_Click(object sender, EventArgs e)
{ FinalVideo = new VideoCaptureDevice(VideoCaptureDevices[comboBox1.SelectedIndex].MonikerString);
  FinalVideo.NewFrame += new  NewFrameEventHandler(FinalVideo_NewFrame);
  FinalVideo.Start();
}

Answer 1

Try writing your code like this:

void FinalVideo_NewFrame(object sender, NewFrameEventArgs eventArgs)
{
    Bitmap video = (Bitmap)eventArgs.Frame.Clone();
    pictureBox1.Invoke((Action)(() =>
    {
        pictureBox1.Image = video;
        TextBox1.text = "demo error";
    }));
}

The .Invoke pushes the execution of the Action delegate onto the same thread that created the pictureBox1 control, in order words, the UI thread.