2019-09-25

- (UIImage*)imageByScalingAndCroppingForSize:(CGSize)targetSize {
    CGSize imageSize = self.size;

    CGFloat width = imageSize.width;
    CGFloat height = imageSize.height;

    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;

    CGFloat scaleFactor = 0.0;

    CGFloat scaledWidth = targetWidth;
    CGFloat scaledHeight = targetHeight;

    CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
 
    if (CGSizeEqualToSize(imageSize, targetSize) == NO)  {
   
        CGFloat widthFactor = targetWidth / width;
        CGFloat heightFactor = targetHeight / height;

        if (widthFactor > heightFactor) {
            scaleFactor = widthFactor; // scale to fit height
        }else {
            scaleFactor = heightFactor; // scale to fit width
        }
        scaledWidth= width * scaleFactor;
        scaledHeight = height * scaleFactor;
        // center the image
        if (widthFactor > heightFactor) {
            thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
        }else if (widthFactor < heightFactor) {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
    }
 
    UIGraphicsBeginImageContext(targetSize); // this will crop
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.origin = thumbnailPoint;
    thumbnailRect.size.width= scaledWidth;
    thumbnailRect.size.height = scaledHeight;
    [self drawInRect:thumbnailRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
 
    if(newImage == nil) {
      NSLog(@"无法缩放图像");
    }  
    //弹出上下文以返回默认值
    UIGraphicsEndImageContext();
 
    return newImage;
}