Question

I want to retrive a value from a NSDictionary.

Here is a snippet of code:

NSDictionary *metadataDict = [representation metadata]; 
NSLog(@"%@",metadataDict);

“DateTimeOriginal” is the value I want to retrieve from the following output.

{
ColorModel = RGB;
DPIHeight = 72;
DPIWidth = 72;
Depth = 8;
Orientation = 6;
PixelHeight = 1936;
PixelWidth = 2592;
"{Exif}" =     {
    ApertureValue = "2.970854";
    ColorSpace = 1;
    ComponentsConfiguration =         (
        1,
        2,
        3,
        0
    );
    DateTimeDigitized = "2011:09:28 09:35:36";
    DateTimeOriginal = "2011:09:28 09:35:36";
    ExifVersion =         (
        2,
        2,
        1
    );
    ExposureMode = 0;
    ExposureProgram = 2;
    ExposureTime = "0.06666667";
    FNumber = "2.8";
    Flash = 24;
    FlashPixVersion =         (
        1,
        0
    );
    FocalLength = "3.85";
    ISOSpeedRatings =         (
        320
    );
    MeteringMode = 5;
    PixelXDimension = 2592;
    PixelYDimension = 1936;
    SceneCaptureType = 0;
    SensingMethod = 2;
    Sharpness = 2;
    ShutterSpeedValue = "3.9112";
    SubjectArea =         (
        1295,
        967,
        699,
        696
    );
    WhiteBalance = 0;
};
"{GPS}" =     {
    Latitude = "37.54216666666667";
    LatitudeRef = N;
    Longitude = "126.95";
    LongitudeRef = E;
    TimeStamp = "01:19:05.00";
};
"{TIFF}" =     {
    DateTime = "2011:09:28 09:35:36";
    Make = Apple;
    Model = "iPhone 4";
    Orientation = 6;
    ResolutionUnit = 2;
    Software = "4.3.5";
    XResolution = 72;
    YResolution = 72;
    "_YCbCrPositioning" = 1;
};

}

I know it’s long but I tried these three and it still would not work.

NSLog(@”valueForKey %@”, [metadataDict valueForKey:@”DateTimeOriginal”]);
NSLog(@”valueForKeyPath %@”, [metadataDict valueForKeyPath:@”DateTimeOriginal”]);
NSLog(@”objectForKey %@”, [metadataDict objectForKey:@”DateTimeOriginal”]);

Does anyone know what kind of datatype is in the NSDictionary and how I can retrieve it?

Thanks much.

Above project link:
http://dl.dropbox.com/u/12439052/TheK2.zip

Answer 1

What you’re really looking for is

NSDictionary *exif = [metadataDict objectForKey:@"{Exif}"];
NSLog(@"DateTimeOriginal: %@", [exif objectForKey:@"DateTimeOriginal"]);

If you read the output from your first log, you’ll see that the key you want is actually inside another dictionary which has the key "{Exif}". Also, -objectForKey: is the better method here to use rather than -valueForKey: (the latter is for generic KVO, the former is the real dictionary object accessor).