I alloc a viewcontroller without init , but why everything works fine

Question

I alloc a viewcontroller without init it, but everything works fine. The subviews in the viewcontroller work fine.

Here is the code.

self.window = [[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];
[self.window makeKeyAndVisible];
self.window.rootViewController = [[UINavigationController alloc]initWithRootViewController:[ViewController alloc]];

The code in ViewController.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self test];
}


- (void)test
{
    self.view.backgroundColor = [UIColor whiteColor];
    CGRect frame = CGRectMake( 50, 100, 200, 200);
    UIScrollView *scrollView= [[UIScrollView alloc] initWithFrame:frame];
    [self.view addSubview:scrollView];
    frame= CGRectMake( 0, 0, 500, 500);
    UIImageView *myImageView= [[UIImageView alloc] initWithFrame:frame];
    [scrollView addSubview:myImageView];
    scrollView.contentSize = CGSizeMake(500,500);

    scrollView.backgroundColor = [UIColor blackColor];
    myImageView.backgroundColor = [UIColor yellowColor];

    scrollView.contentOffset = CGPointMake(0, 0);

}


@end

I put the code of ViewController.m in the question description. — Zentopia, Nov 08 '15 at 12:03
Well, if I remember correctly `init` is mainly just initializing variables. You don't seem to have any global ones, and I'm pretty sure `ViewController` extends `NSObject`, so maybe you don't need to call `init`. — Arc676, Nov 08 '15 at 12:19
Just a hunch. If this question gets more attention someone might be able to give a better answer. — Arc676, Nov 08 '15 at 12:35
It works due to dumb luck. Don't write code like that. It just so happens that UIViewController and its ancestors do not initialize anything critical in `init`. — Avi, Nov 08 '15 at 13:11
@Avi, you should really post your "dumb luck" comment as an answer so the OP can accept it. You were the first to say it. — Duncan C, Nov 08 '15 at 15:17

score 0 · Accepted Answer · answered Nov 08 '15 at 13:43

Avi got it right in (his?) comment. It's dumb luck. This is like saying "I've been driving my car for 30,000 km without changing the oil and it's running fine. Why does everybody say you have to change your oil?"

Init does the setup for a class, and it's ancestor classes. It's fairly certain that there is some setup that isn't getting done that will cause problems in the future.

The proper way to create an object is with alloc/init. If you don't do that, "the result is undefined."

I alloc a viewcontroller without init , but why everything works fine

1 Answers1