常用属性:frame,bounds和center
重要方法 :addSubview 把一个子控件添加到一个父控件中;Superview 返回子控件的父控件
常用函数:- (void)removeFromSuperview;
- (void)insertSubview:(UIView *)view atIndex:
(NSInteger)index;
- (void)exchangeSubviewAtIndex:
(NSInteger)index1
withSubviewAtIndex:(NSInteger)index2;
- (void)addSubview:(UIView *)view;
- (UIView *)viewWithTag:(NSInteger)tag;