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Check Boxes

A check box consists of a square box and application-defined text (label), an icon, or a bitmap, that indicates a choice the user can make by selecting the button. Applications typically display check boxes in a group box to permit the user to choose from a set of related, but independent options. For example, an application might present a group of check boxes from which the user can select error conditions that produce warning beeps.

A check box can be one of four styles: standard, automatic, three-state, and automatic three-state, as defined by the constants BS_CHECKBOX, BS_AUTOCHECKBOX, BS_3STATE, and BS_AUTO3STATE, respectively. Each style can assume two check states: checked (a check mark inside the box) or cleared (no check mark). In addition, a three-state check box can assume an indeterminate state (a grayed box inside the check box). Repeatedly clicking a standard or automatic check box toggles it from checked to cleared and back again. Repeatedly clicking a three-state check box toggles it from
checked to cleared to indeterminate and back again.

When the user clicks a check box (of any style), the check box receives the keyboard focus. The system sends the check box's parent window a WM_COMMAND message containing the BN_CLICKED notification code. The parent window doesn't acknowledge this message if it comes from an automatic check box or automatic threestate check box, because the system automatically sets the check state for those styles. But the parent window must acknowledge the message if it comes from a check box or three-state check box because the parent window is responsible for setting the check state Using Dialogs and Windows Controls 11 for those styles. Regardless of the check box style, the system automatically repaints the check box once its state is changed.

Group Boxes

A group box is a rectangle that surrounds a set of controls, such as check boxes or radio buttons, with application-defined text (label) in its upper left corner. The sole purpose of a group box is to organize controls related by a common purpose (usually indicated by the label). The group box has only one style, defined by the constant BS_GROUPBOX. Because a group box cannot be selected, it has no check state, focus state, or push state. An application cannot send messages to a group box.

Owner Drawn Buttons

Unlike radio buttons, an owner-drawn button is painted by the application, not by the system, and has no predefined appearance or usage. Its purpose is to provide a button whose appearance and behavior are defined by the application alone. There is only one owner-drawn button style: BS_OWNERDRAW.
When the user selects an owner-drawn button, the system sends the button's parent window a WM_COMMAND message containing the BN_CLICKED notification code, just as it does for a button that is not owner-drawn. The application must respond appropriately.

Push Buttons

A push button is a rectangle containing application-defined text (label), an icon, or a bitmap that indicates what the button does when the user selects it. A push button can be one of two styles: standard or default, as defined by the constants BS_PUSHBUTTON and BS_DEFPUSHBUTTON. A standard push button is typically used to start an operation. It receives the keyboard focus when the user clicks it. A default push button, on the other hand, is typically used to indicate the most common or default choice. It is a button that the user can select by simply pressing ENTER when a dialog box has the input focus. When the user clicks a push button (of either style), it receives the keyboard focus. The system sends the button's parent window a WM_COMMAND message that contains the BN_CLICKED notification code. In response, the dialog box typically closes and carries out the operation indicated by the button. The default push button cannot be a check box, a radio button, or an ownerdraw button at the same time. Using Dialogs and Windows Controls 12

Radio Buttons

A radio button consists of a round button and application-defined text (a label), an icon, or a bitmap that indicates a choice the user can make by selecting the button. An application typically uses radio buttons in a group box to permit the user to choose from a set of related, but mutually exclusive options. For example, the application might present a group of radio buttons from which the user can select a format preference for text selected in the client area. The user could select a left-aligned, right-aligned, or centered format by selecting the corresponding radio button. Typically, the user can select only one option at a time from a set of radio buttons. A radio button can be one of two styles: standard or automatic, as defined by the constants BS_RADIOBUTTON and BS_AUTORADIOBUTTON. Each style can assume two check states: checked (a dot in the button) or cleared (no dot in the button). Repeatedly selecting a radio button (standard or automatic) toggles it from checked to cleared and back again.

When the user selects either state, the radio button receives the keyboard focus. The system sends the button's parent window a WM_COMMAND message containing the BN_CLICKED notification code. The parent window doesn't acknowledge this message if it comes from an automatic radio button because the system automatically sets the check state for that style. But the parent window should acknowledge the message if it comes from a radio button because the parent window is responsible for setting the check state for that style. Regardless of the radio button style, the system automatically repaints the button as its state changes. When the user selects an automatic radio button, the system automatically sets the check state of all other radio buttons within the same group to clear. The same behavior is available for standard radio buttons by using the WS_GROUP style, as discussed in Dialog Boxes.