ios关于图片拉伸的版本间的几种方法

1.iOS 5.0之前的做法
- (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight;

2.iOS 5.0的做法
- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets;

3.iOS 6.0的做法
- (UIImage *)resizableImageWithCapInsets:(UIEdgeInsets)capInsets resizingMode:(UIImageResizingMode)resizingMode;