Question

Hello i am newbie in iPhone development can any one help me to know difference between following two lines:

First:

[[[[UIApplication sharedApplication] delegate] window] addSubview:UIView];

Second:

[[UIApplication sharedApplication].keyWindow addSubview:UIView];

Thanks in advance.

Basheer_CAD · Accepted Answer · 2015-04-05 19:07:10Z

They are the same in iOS, but on Mac OS they can be different, because in iOS there is only one window, while on Mac OS could be more than one.
from the documentation:
- For [[[UIApplication sharedApplication] delegate] window];

The window to use when presenting a storyboard. This property contains the window used to present the app’s visual content on the device’s main screen.

i.e this is the property window you have in your appDelegate.h file

for [[UIApplication sharedApplication] keyWindow];

This property holds the UIWindow object in the windows array that is most recently sent the makeKeyAndVisible message.

in iOS you sent makeKeyAndVisible in your appDelegate.m inside
application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
to window, which what we have above, so they are the same. (This is done automatically if you are using storyboards)

Jeffery Thomas · Answer 2 · 2014-02-11 12:07:12Z

For most uses, they will be the same… but not always.

[UIApplication sharedApplication].keyWindow is the window which is currently being displayed on the device. This is normally your application's window, but could be a system window.

[UIApplication sharedApplication].delegate.window is the window your application is expected to use.

Which one should be used? Well that all depends on context.

If you are updating part of your application, then you should add views to your application's window. This is almost always what you want to do.

Personally, I always use [[UIApplication sharedApplication].delegate.window addSubview:view]or [self.view.window addSubView:view] (within UIViewController) when I need to add a view directly to the window.

There might be some times when you want to present a view to the window currently being displayed, regardless if the window belongs to your application or is some system window. I've not run into that situation.

plu · Answer 3 · 2014-02-11 10:09:11Z

The simplest setup is to just have one UIWindow. Usually that window is kept as a property on your app delegate. The keyWindow is the one that is designated to receive keyboard and other non-touch related events. Only one window at a time may be the key window. So if you add a 2nd window and make it the keyWindow (via [window makeKeyAndVisible]), your lines return different windows!

3 Answers