UIButton的探秘

原文链接

sizeToFit()和sizeThatFits(_:)

sizeToFit()会调用sizeThatFits(_:)方法，将现在的frame作为参数。然后根据函数返回的结果更新view。

sizeToFit will simply call through to sizeThatFits: passing the view's current size as the argument. It will then update the view's frame based on the value it gets back. So all the important logic goes in sizeThatFits:, and this is the method you should override for your own custom controls.

UIButton标题的shadow效果与反转

        myButton?.titleLabel?.shadowOffset = CGSizeMake(2.0, 2.0)
        myButton?.setTitleShadowColor(UIColor.redColor(), forState: .Normal)
//        myButton?.showsTouchWhenHighlighted = true
        myButton?.reversesTitleShadowWhenHighlighted = true

加上选中态亮瞎眼的效果

        myButton?.showsTouchWhenHighlighted = true

UIButton的布局与UIEdgeInsets

有三个UIEdgeInsets

1. contentEdgeInsets
   使用sizeThatFits(_:)计算时用到。
2. titleEdgeInsets
   使用sizeThatFits(_:)计算时不会用到。
3. imageEdgeInsets
   使用sizeThatFits(_:)计算时不会用到。

You can specify a different value for each of the four insets (top, left, bottom, right). A positive value shrinks, or insets, that edge—moving it closer to the center of the button. A negative value expands, or outsets, that edge.

举例说明

• contentEdgeInsets
  
  left和right都是30，会使左边向中间移动30pt，右边向中间移动30pt。也就是左间距和右间距都是30pt。由于contentEdgeInsets参与sizeThatFits(_:)的计算，所以最终表现为整个button被拉宽。
• titleEdgeInsets
  
  保持contentEdgeInsets不变，设置titleEdgeInsets的left为15。由于titleEdgeInsets在sizeThatFits(_:)中不参与，因此button没有被拉宽，只是titleLabel的左边向右（中心）移动了15pt，右边保持不变。导致字符串没有被显示全。
  
  设置titleEdgeInsets的right为-15，结果是titleLabel的右边向右移动了15pt，从而整体的显示范围不变。
• imageEdgeInsets

图像在右，标题在左

button.transform = CGAffineTransformMakeScale(-1.0, 1.0);
button.titleLabel.transform = CGAffineTransformMakeScale(-1.0, 1.0);
button.imageView.transform = CGAffineTransformMakeScale(-1.0, 1.0);

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