By default, the system moves the input focus to the next or previous control whenever the user presses a direction key. As long as the current control with the input focus does not process these keys and the next or previous control is not a static control, the system continues to move the input focus through all controls in the dialog box as the user continues to press the direction keys.
An application can use the WS_GROUP style to modify this default behavior. The style marks the beginning of a group of controls. If a control in the group has the input focus when the user begins pressing direction keys, the focus remains in the group. In general, the first control in a group must have the WS_GROUP style and all other controls in the group must not have this style. All controls in the group must be contiguous — that is, they must have been created consecutively with no intervening controls.
When the user presses a direction key, the system first determines whether the current control having the input focus processes the direction keys. The system sends a WM_GETDLGCODE message to the control and if the control returns the DLGC_WANTARROWS value, passes the key to the control. Otherwise, the system uses the GetNextDlgGroupItem function to determine the next control in the group.
GetNextDlgGroupItem searches controls in the order (or reverse order) they were created. If the user presses the right or down key, GetNextDlgGroupItem returns the next control if that control does not have WS_GROUP style. Otherwise, the function reverses the order of the search and returns the first control that has the WS_GROUP style. If the user presses the left or up key, the function returns the previous control unless the current control already has the WS_GROUP style. If the current control has this style, the function reverses the order of the search, locates the first control having the WS_GROUP style, and returns the control that immediately precedes the located control.
Once the system has the next or previous control, it sends a WM_GETDLGCODE message to the control to determine the control type. The system then moves the input focus to control if it is not a static control. If the control is an automatic radio button, the system sends a BM_CLICK message to it. An application can also use GetNextDlgGroupItem to locate controls in a group.
Generally, the first control in the group combines the WS_GROUP and WS_TABSTOP styles so that the user can move from group to group by using the tab key. If the group contains radio buttons, the application should apply the WS_TABSTOP style only to the first control in the group. The system automatically moves the style when the user moves between controls in the group. This ensures that the input focus will always be on the most recently selected control when the user moves to the group using the tab key.