IOS之UI -- 按钮UIButton的细节

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按钮细节

文章概要：

1、内部子控件
2、按钮拉伸问题
    2-1、代码拉伸
    2-2、无代码拉伸

内部子控件

如果想要改变按钮内部子控件的属性，只能自定义按钮

• 自定义按钮：调整内部子控件的frame
  • 方式1：实现titleRectForContentRect:和imageRectForContentRect:方法，分别返回titleLabel和imageView的frame
  • 方式2：在layoutSubviews方法中设置
• 内边距

// 设置按钮内容的内边距（影响到imageView和titleLabel）
@property(nonatomic)          UIEdgeInsets contentEdgeInsets;
// 设置titleLabel的内边距（影响到titleLabel）
@property(nonatomic)          UIEdgeInsets titleEdgeInsets;
// 设置imageView的内边距（影响到imageView）
@property(nonatomic)          UIEdgeInsets imageEdgeInsets;

调整内部子控件的frame的方法1但是这样写很麻烦，而且有个问题：

　　如果两个方法内部的参数互相依赖，但是却不清楚两个方法的执行顺序，所以容易出现异常。

然后建议使用调整内部子控件的frame方法2，在layoutSubviews中设置子控件的frame。

按钮其实不需要添加子控件的，因为按钮内部有两个子控件UIImage和UILabel，可以直接使用，但是对于这两个子控件使用有一些注意点：UIButton的子控件的iamgeView.image和titleLabel.text不能直接设置值，因为这两个值(或许还有别的值，可以通过看源码查看注释)是需要有设置状态属性值，如果没有设置状态，直接访问其属性更改会失效。

所以，以后按钮内置子控件的属性，要先确认是否需要分状态显示的。

如果想要该自己改变子控件titileLabel的字体，直接拿出font赋值，因为font不分状态

按钮拉伸问题

代码拉伸

在按钮使用了背景图片之后，特别是圆角图片，如果将按钮拉伸很大，边角锯齿显示就很明显了，也很难看。

所以我们需要将按钮拉伸问题进行处理：

使用UIImage对象的一个方法resizeable...可拉伸的意思

瓦片模式：拉伸后，会将可拉伸的部分拷贝铺设一块一块
拉伸模式：拉伸后，会直接将可拉伸部分直接拉大

瓦片模式，如果可拉伸部分是纯单色，跟拉伸模式没区别

• iOS5之前

// 只拉伸中间的1x1区域
- (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight;

• iOS5开始

- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets;
- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets resizingMode:(UIImageResizingMode)resizingMode;

最后一般项目中这个图片拉伸的复用的功能我们可以封装在内部，
我们先将这个功能封装进方法，方法名是：resizableImage
那么写在谁的内部比较合适,也就是谁做这个功能最合适呢？
当然是UIImage，那么就有两种方式，
    1、分类类别拓展UIImage的方法，2、在继承UIImage自定义类中写
注意：类别拓展拓展成类方法比较合适哦，不然你还需要通过alloc-init创建UIImage对象，然后调用这个拓展的类别方法。

无代码拉伸

在xcode上设置，直接好使用，不用写代码，一劳永逸。连前面导入类别文件名都不需要了。