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# metadata

The metadata for this HealthKit object.

```
var metadata: [String : Any]? { get }
```

## Discussion

The metadata dictionary contains extra information describing this object. The dictionary’s keys are all <doc://com.apple.documentation/documentation/Foundation/NSString> objects. The values can be <doc://com.apple.documentation/documentation/Foundation/NSString> objects, <doc://com.apple.documentation/documentation/Foundation/NSNumber> objects or <doc://com.apple.documentation/documentation/Foundation/NSDate> objects. For a complete list of predefined metadata keys, see <doc://com.apple.healthkit/documentation/HealthKit/metadata-keys>.

Using predefined keys helps facilitate sharing data between apps; however, you are also encouraged to create your own, custom keys as needed to extend the HealthKit object’s capabilities.

You set an object’s metadata when you create the object by calling one of these methods (or a related method):

- [`init(type:quantity:start:end:metadata:)`](/documentation/HealthKit/HKQuantitySample/init(type:quantity:start:end:metadata:))
- [`init(type:value:start:end:metadata:)`](/documentation/HealthKit/HKCategorySample/init(type:value:start:end:metadata:))
- [`init(type:start:end:objects:metadata:)`](/documentation/HealthKit/HKCorrelation/init(type:start:end:objects:metadata:))
- [`init(activityType:start:end:duration:totalEnergyBurned:totalDistance:metadata:)`](/documentation/HealthKit/HKWorkout/init(activityType:start:end:duration:totalEnergyBurned:totalDistance:metadata:))

---

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