Page 128 - DCAP408_WEB_PROGRAMMING

Windows Programming

Notes When the user uses an accelerator that corresponds to a menu item, the window procedure
receives the WM_INITMENU and WM_INITMENUPOPUP messages as though the user had
selected the menu item. For information about how to process these messages, see Menus.
An accelerator that corresponds to a menu item should be included in the text of the menu item.

7.11.5 UI State

Windows enables applications to hide or show various features in its UI. These settings are
known as the UI state. The UI state includes the following settings:

 focus indicators (such as focus rectangles on buttons)
 keyboard accelerators (indicated by underlines in control labels)
A window can send messages to request a change in the UI state, can query the UI state, or
enforce a certain state for its child windows. These messages are as follows.
MessageDescription
WM_CHANGEUISTATE Indicates that the UI state should change.

WM_QUERYUISTATE Retrieves the UI state for a window.
WM_UPDATEUISTATE Changes the UI state.
By default, all child windows of a top-level window are created with the same UI state as their
parent.
The system handles the UI state for controls in dialog boxes. At dialog box creation, the system
initializes the UI state accordingly. All child controls inherit this state. After the dialog box is
created, the system monitors the user's keystrokes. If the UI state settings are hidden and the
user navigates using the keyboard, the system updates the UI state. For example, if the user
presses the Tab key to move the focus to the next control, the system calls WM_CHANGEUISTATE
to make the focus indicators visible. If the user presses the Alt key, the system calls
WM_CHANGEUISTATE to make the keyboard accelerators visible.
If a control supports navigation between the UI elements it contains, it can update its own UI
state. The control can call WM_QUERYUISTATE to retrieve and cache the initial UI state. Whenever
the control receives an WM_UPDATEUISTATE message, it can update its UI state and send a
WM_CHANGEUISTATE message to its parent. Each window will continue to send the message
to its parent until it reaches the top-level window. The top-level window sends the
WM_UPDATEUISTATE message to the windows in the window tree. If a window does not pass
on the WM_CHANGEUISTATE message, it will not reach the top-level window and the UI state
will not be updated.
Self Assessment

Fill in the blanks:
15. An ......................... table includes an array of ACCEL structures, each defining an individual
accelerator.
16. The WM_COMMAND message comprises the identifier of the accelerator that caused
......................... to produce the message.

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