• 如果想要拉伸一个图片，直接拉伸的话，图片有透明的区域会拉伸变形，需要设置保护的区域方法可以分为两种
  1. 通过代码

  UIImageView *imageView =[[UIImageView alloc]init];
    imageView.frame = CGRectMake(10, 10, 200, 100);
    [self.view addSubview:imageView];
    //加载原图
    UIImage *image =[UIImage imageNamed:@"chat_send_press_pic"];
    
    //拉伸处理 UIEdgeInsetsMake 需要保护的区域
//    image = [image resizableImageWithCapInsets:UIEdgeInsetsMake(30, 30, 30, 30) resizingMode:UIImageResizingModeStretch];
//    imageView.image = image;
    
    /**
     *  一个图片有上下左右位置,stretchableImageWithLeftCapWidth方法是算出1*1的像素不保护
     * leftCapWidth :width - left - right - 1
     * topCapHeight :height - top - bottom - 1
     */
    image = [image stretchableImageWithLeftCapWidth:image.size.width * 0.5 topCapHeight:image.size.height * 0.5];
    
    imageView.image = image;

2. 在Assset文件中设置