我通过以下2种方法将有关位置的metadata信息写入照片：

1. 将位置信息写入image,让后调用系统api将图片保存到相册

- (void)writeImageDataToSavedPhotosAlbum:(NSData *)imageData metadata:(NSDictionary *)metadata resultBlock:(PHAssetAssetBoolBlock)resultBlock
{
    __block PHObjectPlaceholder *placeholderAsset = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
        UIImage *image = [self imageWithData: imageData metadata:metadata];
        [PHAssetChangeRequest creationRequestForAssetFromImage: image];
        placeholderAsset = newAssetRequest.placeholderForCreatedAsset;
    } completionHandler:^(BOOL success, NSError *error) {
        if(success){
            PHAsset *asset = [self getAssetFromlocalIdentifier:placeholderAsset.localIdentifier];
            completionBlock(asset, YES);
        } else {
            completionBlock(nil, NO);
        }
    }];
}

- (UIImage *)imageWithData:(NSData *)imageData metadata:(NSDictionary *)metadata
{
    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
    NSMutableDictionary * sourceDic = [NSMutableDictionary dictionary];
    NSDictionary *source_metadata = (NSDictionary *)CFBridgingRelease(CGImageSourceCopyProperties(source, NULL));
    [sourceDic addEntriesFromDictionary: metadata];
    [sourceDic addEntriesFromDictionary:source_metadata];
    
    NSMutableData *dest_data = [NSMutableData data];
    CFStringRef UTI = CGImageSourceGetType(source);
    CGImageDestinationRef destination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)dest_data, UTI, 1,NULL);
    CGImageDestinationAddImageFromSource(destination, source, 0, (__bridge CFDictionaryRef)sourceDic);
    CGImageDestinationFinalize(destination);
    CFRelease(source);
    CFRelease(destination);
    return [UIImage imageWithData: dest_data];
}

2.用PHAssetChangeRequest的location属性保存，代码如下：

    +(void)saveImageToCameraRoll:(UIImage*)image location:(CLLocation*)location completionBlock:(PHAssetAssetBoolBlock)completionBlock{
    __block PHObjectPlaceholder *placeholderAsset = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
        PHAssetChangeRequest *newAssetRequest = [PHAssetChangeRequest creationRequestForAssetFromImage:image];
        newAssetRequest.location = location;
        newAssetRequest.creationDate = [NSDate date];
        placeholderAsset = newAssetRequest.placeholderForCreatedAsset;
    } completionHandler:^(BOOL success, NSError *error) {
        if(success){
            PHAsset *asset = [self getAssetFromlocalIdentifier:placeholderAsset.localIdentifier];
            completionBlock(asset, YES);
        } else {
            completionBlock(nil, NO);
        }
    }];
}

然后获取照片的metadata信息，发现没有关于GPS的信息，获取方法如下：

- (void)getPhotoMetadataWithAsset:(PHAsset *)asset
{
    PHImageRequestOptions *request = [PHImageRequestOptions new];
    request.version = PHImageRequestOptionsVersionCurrent;
    request.deliveryMode = PHImageRequestOptionsDeliveryModeHighQualityFormat;
    request.resizeMode = PHImageRequestOptionsResizeModeNone;
    request.synchronous = YES;
    
    [[PHImageManager defaultManager] requestImageDataForAsset:asset options: request resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {
        CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
        if (NULL != source) {
            NSDictionary * metadataDic = (NSDictionary *)CFBridgingRelease(CGImageSourceCopyPropertiesAtIndex(source, 0, NULL));
            NSLog(@"metada:%@",metadataDic);
            CFRelease(source);
        }
    }];
}

麻烦看下是保存metadata过程有问题？还是获取metadata有问题？