I want to create a PlusWnd which is always opposite with a ChatWnd, means their position can be adjusted at the same time (likes the playlist panel of winamp).

I've considered using setParent to make the PlusWnd be a child of the ChatWnd. But the PlusWnd even can't be shown if it is outside the border of the ChatWnd. How can I adjust the border of the ChatWnd and solve the problem?

Thank you very much!!

You cannot do it with SetParent then. You got to subclass the chat window, and look for movement/resize messages.

Or you can actually do it a quite bad way, using timers, moving the window to fit the chat window.

You can't make a child window exceed it's parents boundaries. That's not what a child window is supposed to do. According to your screenshot, you want to make a search field. (which is a pretty nice idea! ) I recommend you to subclass the chat window and move your PlusWnd when you receive a WM_SIZE (and eventually a WM_SIZING) message and change the positions of your child window based on the new window rectangle.

This may be tricky, so if you need help with it, PM me with your e-mail address and I'll try to help you out. I'll have to do some research on how to subclass windows first myself too, but once we have a WM_SIZE message, it'll be easy to move the child window.