UIButton with GradientLayer obscures image and darkens gradient

问题

I have an UIButton here where I'd like to have a gradient as the background below the image (symbol with transparent background), but I'm facing two different problems.

First of the CAGradientLayer seems to overlay on top of the image no matter how I try to add it, obscuring the image completely.

Secondly the gradient itself seems to be darkened a lot, like the button was disabled, which it isn't.

Here's my code:

self.backButton = [[UIButton alloc] initWithFrame:CGRectMake(15, 35, 28, 28)];
[backButton addTarget:self
               action:@selector(goBack)
     forControlEvents:UIControlEventTouchUpInside];
[backButton setBackgroundColor:[UIColor clearColor]];
CAGradientLayer *buttonGradient = [CAGradientLayer layer];
buttonGradient.frame = backButton.bounds;
buttonGradient.colors = [NSArray arrayWithObjects:
                         (id)[[UIColor colorWithRed:.0
                                              green:.166
                                               blue:.255
                                              alpha:1] CGColor], 
                         (id)[[UIColor colorWithRed:.0
                                              green:.113
                                               blue:.255
                                              alpha:1] CGColor], 
                         nil];
[buttonGradient setCornerRadius:backButton.frame.size.width / 2];
[backButton.layer insertSublayer:buttonGradient
                         atIndex:0];
[backButton setImage:[UIImage imageNamed:@"backarrow.png"]
            forState:UIControlStateNormal];
[backButton setEnabled:NO];
[topbarView addSubview:backButton];

回答1:

So I managed to get around this by doing a [button bringSubviewToFront:button.imageView] after adding the gradient. Seems that no matter what I do the new layer will add on top of the imageView, so I need to push that to the front afterwards.

Objective-C:

[button bringSubviewToFront:button.imageView]

Swift 4.1:

button.bringSubview(toFront:button.imageView!)

回答2:

Alternatively, you can insert the gradient layer below the image view's layer

CAGradientLayer* gradient = [CAGradientLayer layer];
// ...
[button.layer insertSublayer:gradient below:button.imageView.layer];

回答3:

SWIFT 3

Here goes an example: (Based on Neil answer)

    let layer = CAGradientLayer()
    layer.frame = CGRect(x: 0, y: 0, width: myButtonOutlet.layer.frame.size.width, height: myButtonOutlet..layer.frame.size.height)
    layer.colors = [UIColor.white.cgColor, pixelColorReceta.cgColor]
    layer.masksToBounds = true
    layer.cornerRadius = myButtonOutlet.layer.cornerRadius
    myButtonOutlet.layer.insertSublayer(layer, below: myButtonOutlet..imageView?.layer)

Happy coding :)

回答4:

Swift 3

You can move the image above the gradient:

button.imageView?.layer.zPosition = 1

or insert the gradient under the image:

button.layer.insertSublayer(gradientLayer, below: button.imageView?.layer)

来源：https://stackoverflow.com/questions/8106637/uibutton-with-gradientlayer-obscures-image-and-darkens-gradient

标签

ios

uibutton

calayer

cagradientlayer