Overriding init in subclass

Question

In Objective-C, is it necessary to override all inherited constructors of a subclass to add custom initialization logic?

For example, would the following be correct for a UIView subclass with custom initialization logic?

@implementation CustomUIView

- (id)init {
    self = [super init];
    if (self) {
        [self initHelper];
    }
    return self;
}

- (id)initWithFrame:(CGRect)theFrame {
    self = [super initWithFrame:theFrame];
    if (self) {
        [self initHelper];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)decoder {
    self = [super initWithCoder:decoder];
    if (self) {
        [self initHelper];
    }
    return self;
}

- (void) initHelper {
    // Custom initialization
}

@end

Answer 1

Every Cocoa Touch (and Cocoa) class has a designated initializer; for UIView, as stated in this documentation, that method is initWithFrame:. In this particular case, you'll only need to override initWithFrame; all other calls will cascade down and hit this method, eventually.

This goes beyond the scope of the question, but if you do end up creating a custom initializer with extra parameters, you should make sure to the designated initializer for the superclass when assigning self, like this:

- (id)initWithFrame:(CGRect)theFrame puzzle:(Puzzle *)thePuzzle title:(NSString *)theTitle {
    self = [super initWithFrame:theFrame];
    if (self) {
        [self setPuzzle:thePuzzle];
        [self setTitle:theTitle];
        [self initHelper];
    }
    return self;
}