如何设置圆形图像的背景颜色？

Question

我有一个图像，点击一个按钮，它的alpha会随着它的黑暗而改变。

我想到这样做的最好方法如下：

cell.followUserImage.backgroundColor = UIColor.blackColor().colorWithAlphaComponent(0.5)

以下是更改前的图片：

以下是以下图片：

正如你所看到的，它只会使角落变暗。我希望它只是使图像变暗并改变其alpha分量。

我将如何做到这一点？

Answer 1

来自@Rob的好主意

以下是 Swift 3 中的代码：

let mask = UIImageView(frame: imageView.bounds)
mask.image = imageView.image
mask.contentMode = imageView.contentMode
imageView.mask = mask

let overlay = UIView(frame: imageView.bounds)
overlay.backgroundColor = UIColor(white: 0, alpha: 0.2)
imageView.addSubview(overlay)

要使整个imageView半透明，您可以设置它的alpha：

imageView.alpha = 0.5     

Answer 2

如果要创建一个暗淡的图像，屏蔽该原始图像，您可以执行以下操作（在Swift 3中）：

with
     test_data ( dt, item ) as (
       select 1, 'A' from dual union all
       select 1, 'B' from dual union all
       select 2, 'C' from dual union all
       select 3, 'A' from dual
     )
-- end of test data; solution (SQL query) begins below this line
select dt, count(*) as ct
from   ( select   min(dt) as dt, item
         from     test_data
         group by item
       )
group by dt
;

        DT         CT
---------- ----------
         1          2
         2          1

其中

with
     test_data ( dt, item ) as (
       select 1, 'A' from dual union all
       select 1, 'B' from dual union all
       select 2, 'C' from dual union all
       select 3, 'A' from dual
     )
-- end of test data; solution (SQL query) begins below this line
select dt, count(case when ord = 1 then 'x' end) as ct
from   (
         select dt, item, count(*) over (partition by item order by dt) ord
         from   test_data
       )
group by dt
;

        DT         CT
---------- ----------
         1          2
         2          1
         3          0

或者，在Swift 2中：

imageView.image = image.darkened()

产生（在暗淡的再现旁边显示图像）：