To create a new UIWindow over the main window

Question

In my app I want to create a new UIWindow over the main UIWindow, And I wrote as following, but it don't works. first, i create a UIWindow as the main window, and then make it key and visible, and then create a new UIWindow overlay, but nothing happens.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {     self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];     self.window.backgroundColor = [UIColor redColor];     ViewController *vc = [[ViewController alloc]initWithNibName:@"ViewController" bundle:nil];     self.window.rootViewController = vc;     [self.window makeKeyAndVisible];     UIWindow *window1 = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, 320, 320)];     window1.backgroundColor = [UIColor redColor];     window1.windowLevel = UIWindowLevelAlert;     [window1 makeKeyAndVisible];     return YES; } 

Answer 1

UIWindow *window1 = [[UIWindow alloc] initWithFrame:CGRectMake(0, 0, 320, 320)]; window1.backgroundColor = [UIColor redColor]; window1.windowLevel = UIWindowLevelAlert; [window1 makeKeyAndVisible]; 

Finally I know why it doesn't work, because window1 is a method var, and it will lost after the method executed. So I declare a new @property for it, as

@property (strong, nonatomic) UIWindow *window2; 

and change the code like

UIWindow *window2 = [[UIWindow alloc] initWithFrame:CGRectMake(0, 80, 320, 320)]; window2.backgroundColor = [UIColor redColor]; window2.windowLevel = UIWindowLevelAlert; self.window2 = window2; [window2 makeKeyAndVisible]; 

it works!

Answer 2

Xcode 8 + Swift

class ViewController: UIViewController {     var coveringWindow: UIWindow?          func coverEverything() {         coveringWindow = UIWindow(frame: (view.window?.frame)!)                  if let coveringWindow = coveringWindow {             coveringWindow.windowLevel = UIWindowLevelAlert + 1             coveringWindow.isHidden = false         }     } } 

According to the documentation, to receive events that do not have a relevant coordinate value, such as keyboard entry, make it key instead of merely ! isHidden:

coveringWindow.makeKeyAndVisible() 

You can even control the transparency of its background, for a smoke effect:

coveringWindow.backgroundColor = UIColor(white: 0, alpha: 0.5) 

Note that such window needs to handle orientation changes.