---

Handling the Display Notice Event as a High-Level Event

To handle the Display Notice event as a high-level event like any other Apple event, you need to

• set the isHighLevelEventAware bit in your application's ' SIZE ' resource to indicate that your application supports high-level events (in which case your application must also support the four required Apple events)
• include code to handle high-level events in your main event loop (as illustrated in Listing 3-1)
• write a function that handles the Display Notice event (as illustrated in Listing 3-2)
• use the AEInstallEventHandler function to install the entry for handling the Display Notice event in your application's Apple event dispatch table

If you want your application to handle all window positioning itself (that is, if you do not want the Display Manager to automatically move any of your windows), you should also set the isDisplayManagerAware bit in the ' SIZE ' resource.

Listing 3-1 Handling Apple events in the event loop

void MyDoEvent(EventRecord *event)
{
    short           part, err;
    WindowPtr       window;
    char            key;
    switch ( event->what ) {
        /* here, handle null, mouse down, key down, update, and 
            other necessary events */
        case kHighLevelEvent:
DoHighLevelEvent(event);
break;
    }
}
void DoHighLevelEvent(EventRecord *event)
{
    OSErr   myErr;
        /* handling only Apple-event types of high-level events */
        myErr = AEProcessAppleEvent(event);
}   

Your application must use the AEInstallEventHandler function to add an entry to your application's Apple event dispatch table. This entry is the function that responds to the Display Notice event. For example, the following code fragment illustrates how to use AEInstallEventHandler to install an application-defined function called DoAEDisplayUpdate .

err = AEInstallEventHandler (kCoreEventClass, 
                            kAESystemConfigNotice, 
                            (ProcPtr)DoAEDisplayUpdate, 0, false);

Listing 3-2 shows an application-defined function called DoAEDisplayUpdate that uses Apple Event Manager functions to obtain information about the various video devices reported by the Display Notice event. The function DoAEDisplayUpdate uses this information to update its internal data structures for its windows and then calls another application-defined function that ensures that its windows are displayed optimally in the new configuration environment.

Listing 3-2 Responding to the Display Notice event

pascal OSErr DoAEDisplayUpdate
(AppleEvent theAE,AppleEvent reply,long ref) {
    #pragma unused(theAE,reply,ref)
    AEDescList      DisplayList;
    AEDescList      DisplayID;
    AERecord        OldConfig,NewConfig;
    AEKeyword       tempWord;
    AEDesc          returnType;
    OSErr           myErr;
    long            result;
    long            count;
    Rect            oldRect, newRect;
    Size            actualSizeUnused;
/* get a list of the displays from the Display Notice event */

    myErr = 
    AEGetParamDesc(&theAE,kAEDisplayNotice,typeWildCard,&DisplayList);

/* count the elements in the list */
    myErr = AECountItems(&DisplayList,&count);
    while (count >0)        /* decode the Display Notice event */
{
        myErr = AEGetNthDesc(&DisplayList, count, typeWildCard, 
            &tempWord, &DisplayID);
        myErr = AEGetNthDesc(&DisplayID, 1, typeWildCard, &tempWord,
            &OldConfig);
        myErr = AEGetKeyPtr(&OldConfig, keyDeviceRect, typeWildCard, 
            &returnType, &oldRect, 8, actualSizeUnused);
        myErr = AEGetNthDesc(&DisplayID, 2, typeWildCard, &tempWord, 
            &NewConfig);
        myErr = AEGetKeyPtr(&NewConfig, keyDeviceRect, typeWildCard, 
            &returnType, &newRect, 8, actualSizeUnused);
/* update internal info about the gdRects for the devices */
        MyUpdateWindowStructures(oldRect, newRect); 
        count--;
}
/* move and resize windows as necessary*/ 
    MyDisplayWindows(); 
    return (noErr);
}