Obj-C, the instance variable used during "self" is not set by the result "[(super or self) init ...]

Question

I know that I recently asked a similar question, but I'm still a little unsure of it. The same thing happens in several places.

Instance variable used when self is not set to result [[(super or self) init ...] '

A

- (id)initWithCoder:(NSCoder *)decoder { if (![super init]) return nil; red = [decoder decodeFloatForKey:kRedKey]; //occurs here green = [decoder decodeFloatForKey:kGreenKey]; blue = [decoder decodeFloatForKey:kBlueKey]; return self; } 

IN

 - (id)initWithFrame:(CGRect)frame title:(NSString*)str sideUp:(BOOL)up{ if(![super initWithFrame:frame]) return nil; int y; UIImage *img; if(up){ img = [UIImage imageNamedTK:@"TapkuLibrary.bundle/Images/graph/popup"]; y = 5; }else{ img = [UIImage imageNamedTK:@"TapkuLibrary.bundle/Images/graph/popdown"]; y = 14; } background = [[UIImageView alloc] initWithImage:img]; // occurs here 

WITH

  - (id) initWithFrame:(CGRect)frame { if(![super initWithFrame:frame]) return nil; UILabel *titleBackground = [[[UILabel alloc] initWithFrame: CGRectMake(0, 0, 480, 40)] autorelease]; titleBackground.backgroundColor = [UIColor whiteColor]; [self addSubview:titleBackground]; titleLabel = [[UILabel alloc] initWithFrame:CGRectZero]; // occurs here 

For block A, this is correct

 self = [self init]; if( self != nil ) { 

And B and C

 - (id) initWithFrame:(CGRect)frame { super = [super initWithFrame:frame] if(super != nil) { 

Answer 1

Typically, you should write:

 self = [super init...]; // Potentially change "self" if (self) { something = x; another = y; } return self; 

This is because init may not return the original value of self in some cases.