Determines whether a button control has a check mark next to it. If the button is a three-state control, the member function determines whether it is dimmed, checked, or neither.

• 这个函数确定一个按钮控件的附加是否具有选中标记。如果按钮是三态控件,则这个函数确定它是变灰、被选中,或都不是。