在iOS中当UI设计的图片满足不了现有需求的时候，比如聊天框、按钮背景在图片大小达不到渲染大小的时候，这个时候就需要你对图片进行拉伸处理了。
chat.png
buttongreen.png
上面两个图片尺寸分别为64x56 和 193x81。如下代码：
UIImageView *imageV = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"chat"]];
imageV.frame = CGRectMake(100, 100, 300, 200);
[self.view addSubview:imageV];
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 400, 200, 200);
[button setBackgroundImage:[UIImage imageNamed:@"buttongreen"] forState:UIControlStateNormal];
[self.view addSubview:button];
对图片和按钮分别不根据图片的尺寸和比例进行设置 渲染结果：
渲染结果.png
chat图片严重失真，buttongreem图片在按钮渲染上也会失真；
对图片拉伸
UIImage *image = [UIImage imageNamed:@"chat"];
CGFloat imageW = image.size.width;
CGFloat imageH = image.size.height;
///分别对图片的 top left bottom right 进行拉伸
UIImage *resizImage = [image resizableImageWithCapInsets:UIEdgeInsetsMake(imageH/2, imageW/2,imageH/2, imageW/2)];
UIImageView *imageV = [[UIImageView alloc] initWithImage:resizImage];
imageV.frame = CGRectMake(100, 100, 300, 200);
[self.view addSubview:imageV];
UIImage *bimage = [UIImage imageNamed:@"buttongreen"];
///分别对图片的 水平 和 垂直 20像素进行拉伸
UIImage *resizBImage = [bimage stretchableImageWithLeftCapWidth:20 topCapHeight:20];
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 400, 200, 200);
[button setBackgroundImage:resizBImage forState:UIControlStateNormal];
[self.view addSubview:button];
渲染结果：
拉伸结果
demo已上传GitHub https://github.com/ShawnWang1/ImageResizing.git
