Why I can't update my UIImageView?

I make my own UIImageView, like this:

@interface MyImageView : UIImageView{


}

And I have the initWithFrame like this:

- (id)initWithFrame{
    if( ( self = [ super initWithFrame: CGRectMake(0, 0, 175, 175) ] ) ) {

    UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"myImage" ofType:@"png"]];
    CGRect cropRect = CGRectMake(175, 0, 175, 175);
    CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], cropRect);   
    //self = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 175, 175)];
    //self.image = [UIImage imageWithCGImage:imageRef];
    [self setImage:[UIImage imageWithCGImage:imageRef]];


    CGImageRelease(imageRef);
    }
    return self;

}

I want to change the image when the user touchesBegin, so I have something like this:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

   UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle] pathForResource:@"myImage2" ofType:@"png"]];
    CGRect cropRect = CGRectMake(0, 0, 175, 175);
    CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], cropRect);   
    //self = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 175, 175)];
    [self setImage:[UIImage imageWithCGImage:imageRef]];
    CGImageRelease(imageRef);
}

I find that I can't change the image. So, I add a line [self addS开发者_如何学运维ubview:imageView]; in the touchesBegan method, that's work. But I have no idea on why I can't change the image from the touchesBegan, thz.

Why are you returning void from initWithFrame??

You should return the initialized object from initWithFrame.

- (id)initWithFrame{    
   if( ( self = [ super initWithFrame: CGRectMake(0, 0, 175, 175) ] ) ) {
       UIImage *img = [UIImage imageWithContentsOfFile: [[NSBundle mainBundle]      pathForResource:@"myImage" ofType:@"png"]];
       CGRect cropRect = CGRectMake(175, 0, 175, 175);
       CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], cropRect);   
       self.image = [UIImage imageWithCGImage:imageRef];
       [self addSubview:imageView];
       CGImageRelease(imageRef);
   }
   return self;
}