網絡圖片下載以后，不能完全平鋪到UIImageView上面，需要所一定的裁剪

- (UIImage *)handleImage:(UIImage *)originalImage

{

    CGSize newSize;

    CGImageRef imageRef =nil;

    if ((originalImage.size.width / originalImage.size.height) < (imageView.frame.size.width / imageView.frame.size.height)) {

        newSize.width = originalImage.size.width;

        newSize.height = originalImage.size.width *self.height /self.width;

        imageRef = CGImageCreateWithImageInRect([originalImageCGImage], CGRectMake(0,fabs(originalImage.size.height - newSize.height) / 2, newSize.width, newSize.height));

    } else {

        newSize.height = originalImage.size.height;

        newSize.width = originalImage.size.height *self.width /self.height;

        imageRef = CGImageCreateWithImageInRect([originalImageCGImage], CGRectMake(fabs(originalImage.size.width - newSize.width) / 2, 0, newSize.width, newSize.height));

    }

    return [UIImageimageWithCGImage:imageRef];

}