Do you need TAB to select a shape and the arrow keys to move it?

Tabbing could be done like this:

private void diagram_KeyDown(object sender, KeyEventArgs e)
{
	if (e.Key == Key.Tab)
	{
		if (diagram.ActiveItem != null)
		{
			if (diagram.ActiveItem is DiagramNode)
			{
				SelectNearestRightNode(diagram.ActiveItem as DiagramNode);
			}
		}
		else
		{
			if (diagram.Nodes.Count > 0)
				diagram.Nodes[0].Selected = true;
		}
	}
}

public void SelectNearestRightNode(DiagramNode selectedNode)
{
	DiagramNode nextNode = null;
	double currDist = double.MaxValue;
	foreach (DiagramNode node in diagram.Nodes)
	{
		if (node.Equals(selectedNode))
			continue;

		double dist = node.Bounds.X - selectedNode.Bounds.X;
		if (dist > 0 && dist < currDist)
		{
			nextNode = node;
			currDist = dist;
		}
	}

	if (nextNode != null)
	{
		diagram.Selection.Clear();
		nextNode.Selected = true;
	}
}
 

Or you might get the index of the ActiveItem in the Diagram.Items collection and select the next item. The arrow keys are intercepted by the ScrollViewer and don't reach the diagram_KeyDown handler. If you want to use them, you will have to add a KeyDown handler higher in the visual tree, to the ScrollViewer or the panel that contains it.

I hope that helps,
Stoyan

Hi Stoyo,

Thanks for the answer!