最近因项目中缺少ios开发，临时客串解决一些ios问题。
在一个需求中，获取到照片的数据，将UIImage写入文件，发现生成的图片是斜的。
朝向向右，而不是向上。
而用UIImageView时能显示正常，因为UIImageView会根据图片旋转容器的方向。
而我们是要把图片上传到服务器，所以这个不行。

然后在网上找到的办法如下：(不行)

+ (UIImage *)fixOrientation:(UIImage *)aImage {

    

    // No-op if the orientation is already correct

    if (aImage.imageOrientation ==UIImageOrientationUp)

        return aImage;

    

    // We need to calculate the proper transformation to make the image upright.

    // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.

    CGAffineTransform transform =CGAffineTransformIdentity;

    

    switch (aImage.imageOrientation) {

        caseUIImageOrientationDown:

        caseUIImageOrientationDownMirrored:

            transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);

            transform = CGAffineTransformRotate(transform, M_PI);

            break;

            

        caseUIImageOrientationLeft:

        caseUIImageOrientationLeftMirrored:

            transform = CGAffineTransformTranslate(transform, aImage.size.width,0);

            transform = CGAffineTransformRotate(transform, M_PI_2);

            break;

            

        caseUIImageOrientationRight:

        caseUIImageOrientationRightMirrored:

            transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);

            transform = CGAffineTransformRotate(transform, -M_PI_2);

            break;

        default:

            break;

    }

    

    switch (aImage.imageOrientation) {

        caseUIImageOrientationUpMirrored:

        caseUIImageOrientationDownMirrored:

            transform = CGAffineTransformTranslate(transform, aImage.size.width,0);

            transform = CGAffineTransformScale(transform, -1, 1);

            break;

            

        caseUIImageOrientationLeftMirrored:

        caseUIImageOrientationRightMirrored:

            transform = CGAffineTransformTranslate(transform, aImage.size.height,0);

            transform = CGAffineTransformScale(transform, -1, 1);

            break;

        default:

            break;

    }

    

    // Now we draw the underlying CGImage into a new context, applying the transform

    // calculated above.

    CGContextRef ctx =CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,

                                             CGImageGetBitsPerComponent(aImage.CGImage),0,

                                             CGImageGetColorSpace(aImage.CGImage),

                                             CGImageGetBitmapInfo(aImage.CGImage));

    CGContextConcatCTM(ctx, transform);

    switch (aImage.imageOrientation) {

        caseUIImageOrientationLeft:

        caseUIImageOrientationLeftMirrored:

        caseUIImageOrientationRight:

        caseUIImageOrientationRightMirrored:

            // Grr...

            CGContextDrawImage(ctx,CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);

            break;

            

        default:

            CGContextDrawImage(ctx,CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);

            break;

    }

    

    // And now we just create a new UIImage from the drawing context

    CGImageRef cgimg =CGBitmapContextCreateImage(ctx);

    UIImage *img = [UIImageimageWithCGImage:cgimg];

    CGContextRelease(ctx);

    CGImageRelease(cgimg);

    return img;

}

该方法不行，在断点调试时发现，是因为该图片UIImage的朝向就是 UIImageOrientationUp。
也就是在已进入这个方法时就return了，下面的都没有执行。
但我们视觉看到的确实是朝向不对，代码检测的却是朝向上。

所以导致该方法不行，我试过去屏蔽掉第一句的判断以及return。但是生成的图片白屏。

还是过其他的办法，发现有的是能旋转过来，但图片的宽高会有问题，导致图片在宽度上被拉伸，高度上被压缩，
即图片的宽高没有对换。

然后发现一个方法： quartz2D来画图片，然后使用ctm变幻来实现旋转

原文地址：https://blog.csdn.net/bitcser/article/details/52055442?utm_source=blogxgwz4

代码如下：

+(UIImage *)image:(UIImage *)image rotation:(UIImageOrientation)orientation

{

    long double rotate = 0.0;

    CGRect rect;

    float translateX = 0;

    float translateY = 0;

    float scaleX = 1.0;

    float scaleY = 1.0;

    

    switch (orientation) {

      case UIImageOrientationLeft:

           rotate =M_PI_2;

           rect =CGRectMake(0,0,image.size.height, image.size.width);

           translateX=0;

           translateY= -rect.size.width;

           scaleY =rect.size.width/rect.size.height;

           scaleX =rect.size.height/rect.size.width;

          break;

      case UIImageOrientationRight:

           rotate =3 *M_PI_2;

           rect =CGRectMake(0,0,image.size.height, image.size.width);

           translateX= -rect.size.height;

           translateY=0;

           scaleY =rect.size.width/rect.size.height;

           scaleX =rect.size.height/rect.size.width;

          break;

      case UIImageOrientationDown:

           rotate =M_PI;

           rect =CGRectMake(0,0,image.size.width, image.size.height);

           translateX= -rect.size.width;

           translateY= -rect.size.height;

          break;

      default:

           rotate =0.0;

           rect =CGRectMake(0,0,image.size.width, image.size.height);

           translateX=0;

           translateY=0;

          break;

    }

    

   UIGraphicsBeginImageContext(rect.size);

  CGContextRef context =UIGraphicsGetCurrentContext();

   //做CTM变换

    CGContextTranslateCTM(context, 0.0, rect.size.height);

    CGContextScaleCTM(context, 1.0, -1.0);

    CGContextRotateCTM(context, rotate);

    CGContextTranslateCTM(context, translateX,translateY);

    

    CGContextScaleCTM(context, scaleX,scaleY);

   //绘制图片

    CGContextDrawImage(context, CGRectMake(0,0,rect.size.width, rect.size.height), image.CGImage);

    

  UIImage *newPic =UIGraphicsGetImageFromCurrentImageContext();

    

    return newPic;

}