一、UIButtonType：按钮样式

typedef NS_ENUM(NSInteger, UIButtonType) {
    UIButtonTypeCustom = 0,                         // no button type
    UIButtonTypeSystem NS_ENUM_AVAILABLE_IOS(7_0),  // standard system button

    UIButtonTypeDetailDisclosure,
    UIButtonTypeInfoLight,
    UIButtonTypeInfoDark,
    UIButtonTypeContactAdd,
    
    UIButtonTypePlain API_AVAILABLE(tvos(11.0)) API_UNAVAILABLE(ios, watchos), // standard system button without the blurred background view
    
    UIButtonTypeRoundedRect = UIButtonTypeSystem   // Deprecated, use UIButtonTypeSystem instead
};

二、UIControlState：按钮的常见状态

typedef NS_OPTIONS(NSUInteger, UIControlState) {
    UIControlStateNormal       = 0,
    UIControlStateHighlighted  = 1 << 0,                  // used when UIControl isHighlighted is set
    UIControlStateDisabled     = 1 << 1,
    UIControlStateSelected     = 1 << 2,                  // flag usable by app (see below)
    UIControlStateFocused NS_ENUM_AVAILABLE_IOS(9_0) = 1 << 3, // Applicable only when the screen supports focus
    UIControlStateApplication  = 0x00FF0000,              // additional flags available for application use
    UIControlStateReserved     = 0xFF000000               // flags reserved for internal framework use
};

按钮的三种常见状态.png

（1）Normal：（Default）

普通状态，未被点击时的显示状态。
对应的枚举常量：UIControlStateNormal

（2）Highlighted：

高亮状态，按钮被按下去但手指为抬起时的显示状态
对应的枚举常量：UIControlStateHighlighted

（3）Disabled：

失效，不可被点击状态：属性enabled为NO
对应的枚举常量：UIControlStateDisabled

三、样式的使用

（1）Xib方式创建的button

默认样式为System样式，该样式下button的高亮状态显示是灰灰的；

System样式（1）

System样式（2）

（2）手写方式创建的button

默认为Custom样式，该样式下button的高亮状态显示是亮亮的；

//自定义button样式（以下两种自定义方式效果相同）    
//UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
//button.frame = CGRectMake(100, 100, 100, 100);

UIButton *button = [[UIButton alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
//为被点击时显示的背景图片
[button setBackgroundImage:[UIImage imageNamed:@"add"] forState:UIControlStateNormal];
//被点击（高亮状态）时显示的背景图片
[button setBackgroundImage:[UIImage imageNamed:@"add_highlighted"] forState:UIControlStateHighlighted];
//失效状态下显示的背景图片
[button setBackgroundImage:[UIImage imageNamed:@"add_disabled"] forState:UIControlStateDisabled];
[self.view addSubview:button];

Custom样式（1）

Custom样式（2）