在介绍UIButton的用法前，要先了解一下它的父类UIControl，UIControl是所有具有事件处理功能控件的父类。

而该类控件一般响应事件又有三种形式：基于触摸、基础值、基础编辑。控件的层次关系图如下：

UIControl类的常用方法：

    - (void)addTarget:(id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents; //添加一个事件

    - (void)removeTarget:(id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents; //删除一个事件

它的子类因为继承了这些方法，所以也经常用到，比如UIButton。

以上两个方法的中最后一个参数，UIControlEvents为点击事件，是枚举类型。

    UIControlEventTouchDown                 // 用户按下时触发

    UIControlEventTouchDownRepeat           // 点击次数大于1时触发

    UIControlEventTouchDragInside           // 当触摸在控件内拖动时触发

    UIControlEventTouchDragOutside          // 当触摸在控件之外拖动时触发

    UIControlEventTouchDragEnter            // 当触摸从控件外拖动到内部时

    UIControlEventTouchDragExit             // 当触摸从控件内拖动到外部时

    UIControlEventTouchUpInside             // 在控件内触摸抬起时

    UIControlEventTouchUpOutside            // 在控件外触摸抬起时

    UIControlEventTouchCancel               // 触摸取消事件，设备被锁上或者电话呼叫打断

    UIControlEventValueChanged              // 当控件的值发生改变时

    UIControlEventEditingDidBegin           //文本控件开始编辑时

    UIControlEventEditingChanged            //文本控件的文本改变

    UIControlEventEditingDidEnd             //文本控件结束编辑时

    UIControlEventEditingDidEndOnExit      // 文本控件内通过按下回车键结束编辑时

    UIControlEventAllTouchEvents        // 所有触摸事件

    UIControlEventAllEditingEvents      // 文本编辑的所有事件，for UITextField

    UIControlEventApplicationReserved  // range available for application use

    UIControlEventSystemReserved        // range reserved for internal framework use

    UIControlEventAllEvents         //所有事件

UIButton

常用方法如下：

- (void)setTitle:(NSString *)title forState:(UIControlState)state;                     // default is nil. title is assumed to be single line

- (void)setTitleColor:(UIColor *)color forState:(UIControlState)state;                 // default if nil. use opaque white

- (void)setTitleShadowColor:(UIColor *)color forState:(UIControlState)state;           // default is nil. use 50% black

- (void)setImage:(UIImage *)image forState:(UIControlState)state;                      // default is nil. should be same size if different for different states

- (void)setBackgroundImage:(UIImage *)image forState:(UIControlState)state;            // default is nil

- (void)addTarget:(id)target action:(SEL)action forControlEvents:(UIControlEvents)controlEvents; //添加一个事件

UIControlState也是个枚举类型：

    UIControlStateNormal       //正常状态

    UIControlStateHighlighted   // 高亮状态

    UIControlStateDisabled     //禁用状态

    UIControlStateSelected      // 选中状态

    UIControlStateApplication    // additional flags available for application use

    UIControlStateReserved 

注意：上面的方法中，setTitle和setImage方法不能同时使用，同时使用，只会显示图片，不显示标题。

如果要设置图片和标题，应该setBackgroundImage和setTitle或者自定义一个UIButton的子类来实现。

UIButton各属性设置的实例代码：

    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];

    // 设置frame，与按钮的类型有关

    button.frame = CGRectMake(90, 100, 41, 30);

    // 禁用按钮

    button.enabled = NO;

    // 按钮选中

    button.selected = YES;

    // 设置标题，状态正常

    [button setTitle:@"normal" forState:UIControlStateNormal];

    // 设置标题，状态高亮

    [button setTitle:@"highlighted" forState:UIControlStateHighlighted];

    // 设置标题，状态禁用

    [button setTitle:@"disabled" forState:UIControlStateDisabled];

    // 设置标题，状态选中

    [button setTitle:@"selected" forState:UIControlStateSelected];

    // 设置title的颜色

    [button setTitleColor:[UIColor redColor] forState:UIControlStateNormal];

    //设置标题的字体

    button.titleLabel.font = [UIFont systemFontOfSize:14.0f];

    // 设置背景图片

    [button setBackgroundImage:[UIImage imageNamed:@"love_normal"] forState:UIControlStateNormal];

    [button setBackgroundImage:[UIImage imageNamed:@"love_select"] forState:UIControlStateHighlighted];

    [button setBackgroundImage:[UIImage imageNamed:@"love_select"] forState:UIControlStateSelected];

    // 设置图片

    [button setImage:[UIImage imageNamed:@"love_normal"] forState:UIControlStateNormal];

    [button setImage:[UIImage imageNamed:@"love_select"] forState:UIControlStateSelected];

    // 用户在控件内按下抬起时

    [button addTarget:self action:@selector(touchUpInside:) forControlEvents:UIControlEventTouchUpInside];

    // 用户按下时

    [button addTarget:self action:@selector(down) forControlEvents:UIControlEventTouchDown];

    // 用户按下时

    [button addTarget:self action:@selector(outside) forControlEvents:UIControlEventTouchUpOutside];

    // 记录用户多次按下

    [button addTarget:self action:@selector(repeat) forControlEvents:UIControlEventTouchDownRepeat];

    // 用户由内向外

    [button addTarget:self action:@selector(dragExit) forControlEvents:UIControlEventTouchDragExit];

    // 用户由外向内

    [button addTarget:self action:@selector(dragEnter) forControlEvents:UIControlEventTouchDragEnter];

    // 事件的取消

    [button addTarget:self action:@selector(cancel) forControlEvents:UIControlEventTouchCancel];

注意了，如果想要UIButton的背景图片显示一张网络图片的话，可以用SDWebImage这个开源框架。