button背景图片拉伸不变形

• (UIImage ) resizableImage:(NSString ) imageName {
  UIImage image = [UIImage imageNamed:imageName];
  // 取图片底部的1 x 1进行拉伸 中部是/2
  UIEdgeInsets insets = UIEdgeInsetsMake(image.size.height4/5, image.size.width4/5, image.size.height4/5 + 1, image.size.width*4/5 + 1);

  return [image resizableImageWithCapInsets:insets];
  }