I have a dialog that is created from a definition in a resource file with a call to CreateDialog. It has a resizing border, and only one control - a Treeview control that takes up the entire window. I know that I need to handle WM_SIZE when the window gets resized and tell the Treeview control that it needs to change its size as well, but I'm missing two critical pieces of information. I can't figure out how to get a handle to the Treeview control (I communicate with it using SendDlgItemMessage()), and I can't figure out what message to send it once I have its handle. How do I do this?