How do you change UIButton image alpha on disabled state?

Question

I have a UIButton with an image and on its disabled state, this image should have .3 alpha.

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
UIIm         


        

Answer 1

Credit goes to @bryanmac for his helpful answer. I used his code as a starting point, but found the same thing can be achieved without using a UIImageView.

Here's my solution:

- (UIImage *)translucentImageFromImage:(UIImage *)image withAlpha:(CGFloat)alpha
{
    CGRect rect = CGRectZero;
    rect.size = image.size;

    UIGraphicsBeginImageContext(image.size);
    [image drawInRect:rect blendMode:kCGBlendModeScreen alpha:alpha];
    UIImage * translucentImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return translucentImage;
}

Set the button's background image for disabled state:

UIImage * disabledBgImage = [self translucentImageFromImage:originalBgImage withAlpha:0.5f];
[button setBackgroundImage:disabledBgImage forState:UIControlStateDisabled];

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EDIT:

I refined my solution further by creating a category on UIImage with this method:

- (UIImage *)translucentImageWithAlpha:(CGFloat)alpha
{
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
    CGRect bounds = CGRectMake(0, 0, self.size.width, self.size.height);
    [self drawInRect:bounds blendMode:kCGBlendModeScreen alpha:alpha];

    UIImage * translucentImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return translucentImage;
}

Set the button's background image for disabled state:

UIImage * disabledBgImage = [originalBgImage translucentImageWithAlpha:0.5f];
[button setBackgroundImage:disabledBgImage forState:UIControlStateDisabled];