如何优雅地在Storyboard中设置圆角

心已赠人 2022-05-19 23:41 443阅读 0赞

### 通常做法 ###

对于代码党来说，很简单的加上一行代码就能够搞定：

对于 Storyboard 狂魔，一般情况下，很多人会先把视图拉一个 IBOutlet 然后再到 `awakeFromeNib:` 或者 `viewDidLoad:` 方法中去设置圆角，代码如下：

但是对代码有一定洁癖的强迫症患者来说，这样的做法经常是要命的！实在无法忍受一个小小圆角都不能在IB中设置，需要另外单独加一行代码来完成，违背了低耦合，高内聚的原则。有人马上提出建议，那就使用IB的运行时属性（Runtime Attributes），有些新手可能对它还不太熟悉：

![IB的运行时属性设置][IB]

这的确也是个不错的方法，可以达到高内聚的效果。不过用过的人都知道，很容易就把 keyPath 拼写错，而且由于这个设置和其他属性的设置分开，可读性可以说很差很差。那有没有什么好的方法呢？

### 最佳实践 ###

Xcode6之后运行时属性升级到了 @IBInspectable ，利用这个我们可以给 UIView 添加一个属性，然后就可以在IB中进行设置，例如我们想给 ViewController 添加一个数值到IB中设置，在上述代码的最前面插入代码：

然后我们就能在属性检查器上看到如图所示内容，很容易地对数值进行设置:

![自定义属性设置][custom_number.png]

> @IBInspectable 还支持以下类型属性：
> 
>  *  Boolean
>  *  Number
>  *  String
>  *  Point
>  *  Size
>  *  Rect
>  *  Range
>  *  Color
>  *  Image
>  *  nil

回到正题，我们视图的圆角该怎么实现呢？也许你们马上想到了继承，实现一个 UIView 的基类，基类中添加圆角的 @IBInspectable 属性。但这样你马上嗅到了不好的味道，你所有想要使用该属性的视图都要继承自该基类，那岂不是更加麻烦！

其实最好的解决方法你应该心里有数，如果说在 Object-C 中给已有的类添加方法，你肯定马上能想到 Category ！不过可能有些人还没不清楚应该如何在 Category 中添加属性。由于这里我们用的是 Swift ，稍后我们再说OC中应该如何实现。 Swift 中应该使用 extension 来对 UIView 进行扩展，并且我们需要添加 @IBInspectable 来扩展属性，所以我们需要同时实现 setter & getter ，创建一个命名为 `UIView+O2CornerRadius.swift` 的文件，代码如下：

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    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"> 
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      layer.cornerRadius = newValue 
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      } 
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      } 
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只需要如此简单地添加一个扩展，不需要 import ，不必任何多余代码，我们就可以非常非常方便地在任意IB的属性检查器中对圆角进行设置了！这不就是我们梦寐以求的解耦吗？！！:)

![自定义圆角属性设置][corner_radius.png]

实际上， @IBInspectable 是对运行时的一种扩展，你所有的设置都会在上述提到的运行时属性（Runtime Attributes）有所体现。

### 接下来做什么？ ###

我们还可以增加很多内容的扩展，例如阴影、边框、边框颜色等等！学会了这样的奇淫技巧，还不赶紧到你的项目中去实践！

说说 Object-C 的代码实现，我们使用 Category 同样需要同时实现 setter & getter :

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   <td style="font-style:inherit;font-family:inherit;font-size:12px;vertical-align:baseline;color:rgb(51,51,51);"><pre style="border:none;font-style:inherit;font-family:'Input Mono', 'PT Mono', Consolas, Monaco, Menlo, monospace;vertical-align:baseline;background:rgb(247,247,247);color:rgb(77,77,76);line-height:1.6;"></pre> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"> 
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     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"><span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(137,89,168);">@implementation</span> <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(62,153,159);">UIView</span> (<span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(62,153,159);">O2CornerRadius</span>)</span> 
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      - ( 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(137,89,168);">void</span>)setCornerRadius:( 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(245,135,31);">CGFloat</span>)cornerRadius 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;">
      { 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"> 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(137,89,168);">self</span>.layer.cornerRadius = cornerRadius; 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;">
      } 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"> 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;">
      - ( 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(245,135,31);">CGFloat</span>)cornerRadius 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;">
      { 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"> 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(137,89,168);">return</span> 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(137,89,168);">self</span>.layer.cornerRadius; 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;">
      } 
    </div> 
    <div style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;"> 
     <span style="border:0px;font-style:inherit;font-family:inherit;vertical-align:baseline;color:rgb(137,89,168);">@end</span> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

出处：凹凸实验室（ [https://aotu.io/notes/2016/03/30/cornerRadius-in-Storyboard/][https_aotu.io_notes_2016_03_30_cornerRadius-in-Storyboard]）

[IB]: http://mark2012.qiniudn.com/runtime_attributes.png
[custom_number.png]: http://mark2012.qiniudn.com/custom_number.png
[corner_radius.png]: http://mark2012.qiniudn.com/corner_radius.png
[https_aotu.io_notes_2016_03_30_cornerRadius-in-Storyboard]: https://aotu.io/notes/2016/03/30/cornerRadius-in-Storyboard/