How to animate transition from one state to another for UIControl/UIButton?

Question

I have a UIButton that changes image on highlight. When transitioning from UIControlStateHighlight to UIControlStateNormal, I want the highlighted image to slowly fade back into the normal image. Is there an easy way to do this?

Answer 1

I ended up subclassing UIButton. Here's the implementation file code. I took some app-specific stuff out, so I haven't tested this exact code, but it should be fine:

#import "SlowFadeButton.h"

@interface SlowFadeButton ()

@property(strong, nonatomic)UIImageView *glowOverlayImgView; // Used to overlay glowing animal image and fade out

@end

@implementation SlowFadeButton



-(id)initWithFrame:(CGRect)theFrame mainImg:(UIImage*)theMainImg highlightImg:(UIImage*)theHighlightImg
{
    if((self = [SlowFadeButton buttonWithType:UIButtonTypeCustom])) {

        self.frame = theFrame;

        if(!theMainImg) {
            NSLog(@"Problem loading the main image\n");
        }
        else if(!theHighlightImg) {
            NSLog(@"Problem loading the highlight image\n");
        }

        [self setImage:theMainImg forState:UIControlStateNormal];
        self.glowOverlayImgView = [[UIImageView alloc] initWithImage:theHighlightImg];
        self.glowOverlayImgView.frame = self.imageView.frame;
        self.glowOverlayImgView.bounds = self.imageView.bounds;

        self.adjustsImageWhenHighlighted = NO;
    }

    return self;
}


-(void)setHighlighted:(BOOL)highlighted
{
    // Check if button is going from not highlighted to highlighted
    if(![self isHighlighted] && highlighted) {
        self.glowOverlayImgView.alpha = 1;
        [self addSubview:self.glowOverlayImgView];
    }
    // Check if button is going from highlighted to not highlighted
    else if([self isHighlighted] && !highlighted) {
        [UIView animateWithDuration:1.0f
                         animations:^{
                             self.glowOverlayImgView.alpha = 0;
                         }
                         completion:NULL];
    }

    [super setHighlighted:highlighted];
}

-(void)setGlowOverlayImgView:(UIImageView *)glowOverlayImgView
{
    if(glowOverlayImgView != _glowOverlayImgView) {
        _glowOverlayImgView = glowOverlayImgView;
    }

    self.glowOverlayImgView.alpha = 0;
}

@end

You could also just pull the highlighted image from [self imageForState:UIControlStateHighlighted] and use that, it should work the same. The main things are to make sure adjustsImageWhenHighlighted = NO, and then overriding the setHighlighted: method.