带有GradientLayer的UIButton会遮挡图像并使渐变变暗 [英] UIButton with GradientLayer obscures image and darkens gradient

问题描述

我在这里有一个UIButton，我想在图像下面有一个渐变作为背景（带有透明背景的符号），但是我遇到了两个不同的问题。

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.

CAGradientLayer中的第一个似乎覆盖在图像的顶部，无论我如何尝试添加它，完全遮盖图像。

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

其次渐变本身似乎它被暗化了很多，就像按钮被禁用一样，它不是。

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

这是我的代码：

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];

推荐答案

所以我设法绕过这个做了[按钮bringSubviewToFront：button.imageView]添加渐变后。似乎无论我做什么，新图层都会添加到imageView之上，所以我需要将其推到前面。

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!)

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