Question

I can’t figure out why that view takes the entire screen.

In AppDelegate file

…

self.viewController = [[[ViewController alloc]init]autorelease];
[self.window setRootViewController:self.viewController];
self.window.backgroundColor = [UIColor whiteColor];

..

In ViewController.m

UIView *view = [[UIView alloc]initWithFrame:CGRectMake(30, 30, 30, 30)];
[view setBackgroundColor:[UIColor greenColor]];
self.view = view;

When I run the app the screen is entirely green instead of having just a square in green.
What is wrong here ?

Answer 1

The erroneous line is here:

self.view = view;

When you set a view of a UIViewController that is the root controller, it is guaranteed to fill the screen. Instead, add it as a subview:

[self.view addSubview:view];

And you should be fine.