UIScreen

UIScreen 對象定義了與硬件顯示的相關屬性，IOS設備有一個主屏幕，0個或是多個附加屏幕，用這個類來獲取附加到設備屏幕的對象，每一個Screen對象都定義了矩形邊界和一些其餘有趣的屬性brightness。

處理通知

• - (void)handleScreenConnectNotification:(NSNotification*)aNotification {

•    UIScreen*    newScreen = [aNotification object];

•    CGRect        screenBounds = newScreen.bounds;

•    if (!_secondWindow) {

•        _secondWindow = [[UIWindow alloc] initWithFrame:screenBounds];

•        _secondWindow.screen = newScreen;

•        // Set the initial UI for the window and show it.

•        [self.viewController displaySelectionInSecondaryWindow:_secondWindow];

•        [_secondWindow makeKeyAndVisible];

•    }

• }

• - (void)handleScreenDisconnectNotification:(NSNotification*)aNotification {

•    if (_secondWindow) {

•        // Hide and then delete the window.

•        _secondWindow.hidden = YES;

•        [_secondWindow release];

•        _secondWindow = nil;

•        // Update the main screen based on what is showing here.

•        [self.viewController displaySelectionOnMainScreen];

•    }

• }