Question

I’m trying to compile this code (the last one):
http://www.aforgenet.com/framework/features/blobs_processing.html

but it throws: Use of unassigned local variable ‘edgePoints’ ..

here is the code:

        BlobCounter blobCounter = new BlobCounter();
        blobCounter.ProcessImage(image23);
        Blob[] blobs = blobCounter.GetObjectsInformation();
        GrahamConvexHull hullFinder = new GrahamConvexHull();
        BitmapData data = image23.LockBits(new Rectangle(0, 0, image23.Width, image23.Height), ImageLockMode.ReadWrite, image23.PixelFormat);
        foreach (Blob blob in blobs)
        {
            List<IntPoint> leftPoints, rightPoints, edgePoints;
            blobCounter.GetBlobsLeftAndRightEdges(blob, out leftPoints, out rightPoints);
            edgePoints.AddRange(leftPoints);
            edgePoints.AddRange(rightPoints);
            List<IntPoint> hull = hullFinder.FindHull(edgePoints);
            Drawing.Polygon(data, hull, Color.Red);
        }
        image23.UnlockBits(data);

And this is the line that he has problem with:

            edgePoints.AddRange(leftPoints);

I tied to assign Null to edgePoints but it failed:

List<IntPoint> leftPoints, rightPoints, edgePoints= null;

What’s the problem? I didn’t modify source code so everything should work..

Answer 1

You need to, well – assign a value to it:

List<IntPoint> leftPoints, rightPoints, edgePoints;
edgePoints = new List<IntPoint>();

Before you call method on that instance.

Your leftPoints and rightPoints are probably initialized by

blobCounter.GetBlobsLeftAndRightEdges(blob, out leftPoints, out rightPoints);

call (note the out keywords), but edgePoints isn’t – you need to do that yourself.