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Handling Events in Response to Display Manager Changes

Users indirectly inform the Display Manager of changes they wish to make to their display environment by using the Monitors control panel, or by attaching or removing additional displays. The Display Manager in turn sends an Apple event--the Display Notice event--to notify applications that the display environment has changed.

After changing the display environment, the Display Manager also generates an update event to notify all current applications to update their windows.

Your application should always handle update events for its windows. However, your application needs to respond to the Display Notice event only if your application repositions its own windows, uses nonstandard windows, or must update any display information that it stores internally.

To receive the Display Notice event informing you of changes to the user's display configuration, you must either

• handle the Display Notice event as a high-level event in your application's normal event loop; or
• use the DMRegisterExtendedNotifyProc function to register a function that handles the Display Notice event as soon as the Display Manager issues it

If you write a utility--such as a control panel--that does not handle events through a normal event loop, or if you want your application to handle the Display Notice event as soon as it is issued instead of waiting for it to appear in the event queue, you should use the DMRegisterExtendedNotifyProc function.

Here is a summary of the Display Notice event (remember that you must use Apple Event Manager functions to obtain the information contained in Apple events such as this):

Display Notice--respond to display configuration changes

Table 3-1 Keyword-specified descriptor structures