What is the difference between UIApplication.sharedApplication.delegate.window and UIApplication.sharedApplication.keyWindow?

Question

Can anyone help me understand the difference between the following two lines:

[UIApplication.sharedApplication.delegate.window addSubview:myView];
         


        

Answer 1

Basheer_CAD's answer is not right. They are not always the same in iOS.

Jeffery Thomas's answer is right and let me provide a concrete example.

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"keyWindow --------> %@",[UIApplication sharedApplication].keyWindow.rootViewController);
    NSLog(@"delegate.window --> %@",[UIApplication sharedApplication].delegate.window.rootViewController);
    NSLog(@"self.view.window -> %@",self.view.window.rootViewController);
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:nil];
    [alert show];
    NSLog(@"keyWindow --------> %@",[UIApplication sharedApplication].keyWindow.rootViewController);
    NSLog(@"delegate.window --> %@",[UIApplication sharedApplication].delegate.window.rootViewController);
    NSLog(@"self.view.window -> %@",self.view.window.rootViewController);
}

The output is:

keyWindow --------> (null)
delegate.window --> 
self.view.window -> (null)
keyWindow --------> 
delegate.window --> 
self.view.window -> 

When viewDidLoad, actually the window is not ready yet, so there is nothing for the system window. UIAlertView may dominate the window, so you cannot get the window you want.