如何实现一个可滚动子对话框

Many times it happened to me (and I hope to you too!) the need for a kind of child dialog, to use as a control inside a more bigger dialog or window or view etc. Filling this child dialog of controls is easy. Set the size of it to fit inside the parent window is not so easy. So, here is the scrollable child dialog, which i found veeeeery useful in my applications