iOS 手机照片上传服务器方向不对的原因以及解决方法

苹果手机上传图片到服务器，发现图片方向不对，实践发现：

1:原因：  相机拍照后直接取出来的UIimage（用UIImagePickerControllerOriginalImage取出），它本身的imageOrientation属性是3，即UIImageOrientationRight。如果这个图片直接使用则没事，但是如果对它进行裁剪、缩放等操作后，它的这个imageOrientation属性会变成0。此时这张图片用在别的地方就会发生旋转。（手机竖着拍则为UIImageOrientationRight，手机横着拍为UIImageOrientationUp）

2:  imageOrientation是只读的，不能直接修改其值。

解决方法：

1. 设置相机的一个属性allowsEditing为YES，设了这个值，你拍完照片后会在照片上出现一个框框，这就是对照片的裁剪编辑。在相机的代理方法中取照片的时候就别用UIImagePickerControllerOriginalImage来取了，要用UIImagePickerControllerEditedImage。用这个key取出来的照片，它的imageOrientation是0，所以之后的任何裁剪、缩放操作都不会造成旋转。

2.由于开发中经常要对原图进行裁剪和压缩，所以第一种方法就不可取了，于是用第二种方法

//调整图片方向

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

    if (srcImg.imageOrientation ==UIImageOrientationUp)return srcImg;

    CGAffineTransform transform =CGAffineTransformIdentity;

    switch (srcImg.imageOrientation) {

        caseUIImageOrientationDown:

        caseUIImageOrientationDownMirrored:

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

            transform = CGAffineTransformRotate(transform,M_PI);

            break;

            

        caseUIImageOrientationLeft:

        caseUIImageOrientationLeftMirrored:

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

            transform = CGAffineTransformRotate(transform,M_PI_2);

            break;

        caseUIImageOrientationRight:

        caseUIImageOrientationRightMirrored:

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

            transform = CGAffineTransformRotate(transform, -M_PI_2);

            break;

        caseUIImageOrientationUp:

        caseUIImageOrientationUpMirrored:

            break;

    }

    switch (srcImg.imageOrientation) {

        caseUIImageOrientationUpMirrored:

        caseUIImageOrientationDownMirrored:

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

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

            break;

            

        caseUIImageOrientationLeftMirrored:

        caseUIImageOrientationRightMirrored:

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

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

            break;

        caseUIImageOrientationUp:

        caseUIImageOrientationDown:

        caseUIImageOrientationLeft:

        caseUIImageOrientationRight:

            break;

    }

    

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

                                             CGImageGetBitsPerComponent(srcImg.CGImage),0,

                                             CGImageGetColorSpace(srcImg.CGImage),

                                             CGImageGetBitmapInfo(srcImg.CGImage));

    CGContextConcatCTM(ctx, transform);

    switch (srcImg.imageOrientation) {

        caseUIImageOrientationLeft:

        caseUIImageOrientationLeftMirrored:

        caseUIImageOrientationRight:

        caseUIImageOrientationRightMirrored:

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

            break;

            

        default:

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

            break;

    }

    

    CGImageRef cgimg =CGBitmapContextCreateImage(ctx);

    UIImage *img = [UIImageimageWithCGImage:cgimg];

    CGContextRelease(ctx);

    CGImageRelease(cgimg);

    return img;

}

直接传入图片，得到纠正方向后的图片