UIView : UIResponder
  /**
通过一个frame来初始化一个UI控件
 */
 - (id)initWithFrame:(CGRect)frame;
 // YES:能够跟用户进行交互
@property(nonatomic,getter=isUserInteractionEnabled) BOOL userInteractionEnabled;  // default is YES
// 控件的一个标记(父控件可以通过tag找到对应的子控件)
@property(nonatomic)                                 NSInteger tag;                // default is 0
// 图层(可以用来设置圆角效果\阴影效果)
@property(nonatomic,readonly,retain)                 CALayer  *layer;
@interface UIView(UIViewGeometry)
// 位置和尺寸(以父控件的左上角为坐标原点(0, 0))
@property(nonatomic) CGRect            frame;
// 位置和尺寸(以自己的左上角为坐标原点(0, 0))
@property(nonatomic) CGRect            bounds;
// 中点(以父控件的左上角为坐标原点(0, 0))
@property(nonatomic) CGPoint           center;      
// 形变属性(平移\缩放\旋转)
@property(nonatomic) CGAffineTransform transform;   // default is CGAffineTransformIdentity
// YES:支持多点触摸
@property(nonatomic,getter=isMultipleTouchEnabled) BOOL multipleTouchEnabled;   // default is NO
@end
@interface UIView(UIViewHierarchy)
 // 父控件
@property(nonatomic,readonly) UIView       *superview;
// 子控件(新添加的控件默认都在subviews数组的后面, 新添加的控件默认都显示在最上面\最顶部)
@property(nonatomic,readonly,copy) NSArray *subviews;
// 获得当前控件所在的window
@property(nonatomic,readonly) UIWindow     *window;
// 从父控件中移除一个控件
- (void)removeFromSuperview;
// 添加一个子控件(可以将子控件插入到subviews数组中index这个位置)
- (void)insertSubview:(UIView *)view atIndex:(NSInteger)index;
// 交换subviews数组中所存放子控件的位置
-  (void)exchangeSubviewAtIndex:(NSInteger)index1 withSubviewAtIndex:(NSInteger)index2;
// 添加一个子控件(新添加的控件默认都在subviews数组的后面, 新添加的控件默认都显示在最上面\最顶部)
- (void)addSubview:(UIView *)view;
// 添加一个子控件view(被挡在siblingSubview的下面)
- (void)insertSubview:(UIView *)view belowSubview:(UIView *)siblingSubview;
// 添加一个子控件view(盖在siblingSubview的上面)
- (void)insertSubview:(UIView *)view aboveSubview:(UIView *)siblingSubview;
// 将某个子控件拉到最上面(最顶部)来显示
- (void)bringSubviewToFront:(UIView *)view;
// 将某个子控件拉到最下面(最底部)来显示
- (void)sendSubviewToBack:(UIView *)view;
/**系统自动调用(留给子类去实现)**/
- (void)didAddSubview:(UIView *)subview;
- (void)willRemoveSubview:(UIView *)subview;
- (void)willMoveToSuperview:(UIView *)newSuperview;
- (void)didMoveToSuperview;
- (void)willMoveToWindow:(UIWindow *)newWindow;
- (void)didMoveToWindow;
/**系统自动调用**/
 // 是不是view的子控件或者子控件的子控件(是否为view的后代)
- (BOOL)isDescendantOfView:(UIView *)view;  // returns YES for self.
 // 通过tag获得对应的子控件(也可以或者子控件的子控件)
- (UIView *)viewWithTag:(NSInteger)tag;     // recursive search. includes self
/**系统自动调用(留给子类去实现)**/
// 控件的frame发生改变的时候就会调用,一般在这里重写布局子控件的位置和尺寸
// 重写了这个写方法后,一定调用[super layoutSubviews];
- (void)layoutSubviews;
@end
@interface UIView(UIViewRendering)
// YES : 超出控件边框范围的内容都剪掉
@property(nonatomic)                 BOOL              clipsToBounds;
// 背景色
@property(nonatomic,copy)            UIColor          *backgroundColor; // default is nil
// 透明度(0.0~1.0)
@property(nonatomic)                 CGFloat           alpha;                      // default is 1.0
// YES:不透明  NO:透明
@property(nonatomic,getter=isOpaque) BOOL              opaque;                     // default is YES
 // YES : 隐藏  NO : 显示
@property(nonatomic,getter=isHidden) BOOL              hidden;
 // 内容模式
 @property(nonatomic)                 UIViewContentMode contentMode;                // default is UIViewContentModeScaleToFill
 @end
 //动画
@interface UIView(UIViewAnimationWithBlocks)
+ (void)animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion;
+ (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion;
+ (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations;
+ (void)animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay usingSpringWithDamping:(CGFloat)dampingRatio initialSpringVelocity:(CGFloat)velocity options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion;
 @end