A button's state can be characterized by its focus state, push state, and check state. The focus state applies to a check box, radio button, push button, or owner-drawn button. A button receives the keyboard focus when the user selects it and loses the focus when the user selects another control. Only one control can have the keyboard focus at a time.
When a button has the keyboard focus, the system typically highlights the text, icon, or bitmap of a button by surrounding it with a dotted line. In addition, a push button has a heavy dark border when it has the focus. Windows automatically changes the highlight for an automatic button, but the application must change the highlight for a nonautomatic button by sending messages.
The push state applies to a push button, check box, radio button, or three-state check box, but does not apply to other buttons. The push state of a button can be either pushed or not pushed. When a push button (or any button with the BS_PUSHLIKE style) is pushed, the button is drawn as a sunken button. When it is not pushed, it is drawn as a raised button. When a check box, radio button, or three-state check box is pushed, the background of the button is grayed. When it is not pushed, the background of the button is not grayed.
The check state applies to a check box, radio button, or three-state check box, but does not apply to other buttons. The state can be checked, unchecked, or (for three-state check boxes) indeterminate. A check box is checked when it contains a check mark, and is unchecked when it does not. A radio button is checked when it contains a black dot; and is unchecked when it does not. A three-state check box is checked when it contains a check mark, is unchecked when it does not, and is indeterminate when it contains a grayed box. Windows automatically changes the check state of an automatic button, but the application must change the check state of a nonautomatic button.