类别添加UIImage的裁剪方法

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首先创建一个UIImage的类别

//.h文件@interface UIImage(UIImageScale)  -(UIImage*)getSubImage:(CGRect)rect;  -(UIImage*)scaleToSize:(CGSize)size;  @end

//.m文件@implementation UIImage(UIImageScale)  //截取部分图像  -(UIImage*)getSubImage:(CGRect)rect  {      CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);      CGRect smallBounds = CGRectMake(0, 0, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));      UIGraphicsBeginImageContext(smallBounds.size);      CGContextRef context = UIGraphicsGetCurrentContext();      CGContextDrawImage(context, smallBounds, subImageRef);      UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];      UIGraphicsEndImageContext();      return smallImage;  }  //等比例缩放  -(UIImage*)scaleToSize:(CGSize)size   {      CGFloat width = CGImageGetWidth(self.CGImage);      CGFloat height = CGImageGetHeight(self.CGImage);      float verticalRadio = size.height*1.0/height;       float horizontalRadio = size.width*1.0/width;      float radio = 1;      if(verticalRadio>1 && horizontalRadio>1)      {          radio = verticalRadio > horizontalRadio ? horizontalRadio : verticalRadio;         }      else      {          radio = verticalRadio < horizontalRadio ? verticalRadio : horizontalRadio;         }      width = width*radio;      height = height*radio;      int xPos = (size.width - width)/2;      int yPos = (size.height-height)/2;      // 创建一个bitmap的context        // 并把它设置成为当前正在使用的context        UIGraphicsBeginImageContext(size);        // 绘制改变大小的图片        [self drawInRect:CGRectMake(xPos, yPos, width, height)];        // 从当前context中创建一个改变大小后的图片        UIImage* scaledImage = UIGraphicsGetImageFromCurrentImageContext();        // 使当前的context出堆栈        UIGraphicsEndImageContext();        // 返回新的改变大小后的图片        return scaledImage;  }  @end

方法的调用

 UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://img21.mtime.cn/mg/2011/09/24/112524.53149978.jpg"]] ];  // 裁剪图片  image = [image getSubImage:CGRectMake(10, 10, 70, 80)];  //等比列缩放  image = [image scaleToSize:CGSizeMake(200, 300)];    NSLog(@"image.size:%@",NSStringFromCGSize(CGSizeMake(imageView.image.size.width, imageView.image.size.height)));   //打印获取的网络图片的宽度和高度

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