使用相机拍摄的照片不包含任何 ALAsset 元数据

最奇怪的事情正在发生。我有一个操作表，用户可以选择使用相机拍照或从相机胶卷中选择一张照片。当 UIImagePicker 从选择返回时，我使用 ALAssetsLibrary 来确定照片中嵌入的 GPS 信息。从相机胶卷中选择照片效果非常好，并且我能够检索 GPS 信息。然而，用相机拍照绝对不提供 GPS 信息，事实上我根本没有元数据。有谁知道我在这里做错了什么？

代码如下：

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{    
    NSString *mediaType = [info objectForKey:UIImagePickerControllerMediaType];
    if([mediaType isEqualToString:(__bridge NSString *)kUTTypeImage])
    {        
        void (^ALAssetsLibraryAssetForURLResultBlock)(ALAsset *) = ^(ALAsset *asset)
        {
            // get images metadata
            NSDictionary *metadata = asset.defaultRepresentation.metadata;
            NSLog(@"Image Meta Data: %@",metadata);

            // get coords 
            CLLocation *location = [asset valueForProperty:ALAssetPropertyLocation];
            NSLog(@"coordLat: %f , coordLon: %f", location.coordinate.latitude, location.coordinate.longitude);

            // do more here - rest of code snipped to keep this question short

    };
    NSURL *assetURL = [info objectForKey:UIImagePickerControllerReferenceURL];
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    [library assetForURL:assetURL
             resultBlock:ALAssetsLibraryAssetForURLResultBlock
            failureBlock:^(NSError *error) 
            {
                // handle error 
            }];

    // rest of code snipped to keep this question short

正如我所解释的，使用相机时会输出以下内容。

2012-04-15 17:58:28.032 MyApp[511:707] Image Meta Data: (null)
2012-04-15 17:58:28.041 MyApp[511:707] coordLat: 0.000000 , coordLon: 0.000000

但是，如果我选择现有照片，或退出应用程序，用相机拍摄一张新照片，然后返回应用程序并从相机胶卷中选择该照片，我会从 NSLog 获得以下输出。

2012-04-15 17:57:03.286 MyApp[511:707] Image Meta Data: {
ColorModel = RGB;
DPIHeight = 72;
DPIWidth = 72;
Depth = 8;
Orientation = 6;
PixelHeight = 1936;
PixelWidth = 2592;
"{Exif}" =     {
    ApertureValue = "2.970854";
    BrightnessValue = "2.886456";
    ColorSpace = 1;
    ComponentsConfiguration =         (
        1,
        2,
        3,
        0
    );
    DateTimeDigitized = "2012:04:15 17:24:02";
    DateTimeOriginal = "2012:04:15 17:24:02";
    ExifVersion =         (
        2,
        2,
        1
    );
    ExposureMode = 0;
    ExposureProgram = 2;
    ExposureTime = "0.06666667";
    FNumber = "2.8";
    Flash = 24;
    FlashPixVersion =         (
        1,
        0
    );
    FocalLength = "3.85";
    ISOSpeedRatings =         (
        80
    );
    MeteringMode = 5;
    PixelXDimension = 2592;
    PixelYDimension = 1936;
    SceneCaptureType = 0;
    SensingMethod = 2;
    Sharpness = 2;
    ShutterSpeedValue = "3.9112";
    SubjectArea =         (
        1295,
        967,
        699,
        696
    );
    WhiteBalance = 0;
};
"{GPS}" =     {
    Altitude = "14.9281";
    AltitudeRef = 0;
    ImgDirection = "107.4554";
    ImgDirectionRef = T;
    Latitude = "32.7366666666667";
    LatitudeRef = N;
    Longitude = "71.679";
    LongitudeRef = W;
    TimeStamp = "21:26:20.00";
};
"{TIFF}" =     {
    DateTime = "2012:04:15 17:24:02";
    Make = Apple;
    Model = "iPhone 4";
    Orientation = 6;
    ResolutionUnit = 2;
    Software = "5.0.1";
    XResolution = 72;
    YResolution = 72;
    "_YCbCrPositioning" = 1;
};
}
2012-04-15 17:57:03.302 MyApp[511:707] coordLat: 32.7366666666667 , coordLon: -71.679

PS - 我正在使用带 ARC 的 xCode 4.3

In - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info

保存照片时尝试此操作

    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
    [library writeImageToSavedPhotosAlbum:image.CGImage
                                 metadata:[info objectForKey:UIImagePickerControllerMediaMetadata]
                          completionBlock:^(NSURL *assetURL, NSError *error) {
        NSLog(@"assetURL %@", assetURL);
    }];