Obj-C，“self”时使用的实例变量未设置为“[(super or self) init...]”的结果

Question

我知道不久前我问过类似的问题，但我仍然有点不确定。同样的事情在很多地方都发生过。

当“self”未设置为“[(super or self) init...]”的结果时使用实例变量

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;
}

B

- (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

C

 - (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

对于块 A，这是正确的

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

并且 B & C

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

Answer 1

一般来说，你应该这样写：

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

这是因为在某些情况下 init 可能不会返回原始的 self 值。