init(type:start:end:objects:metadata:)
Instantiates and returns a new correlation instance with the provided metadata.
Declaration
convenience init(type correlationType: HKCorrelationType, start startDate: Date, end endDate: Date, objects: Set<HKSample>, metadata: [String : Any]?)Parameters
- correlationType:
The type for this correlation. For a complete list of correlation types, see Correlation Types.
- startDate:
The start date for the sample. This date must be equal to or earlier than the end date; otherwise, this method throws an exception (Invalidargumentexception).
- endDate:
The end date for the sample. This date must be equal to or later than the start date; otherwise, this method throws an exception (Invalidargumentexception).
- objects:
A set of Hksample objects. Specifically, this set contains the quantity and category samples to be grouped into this correlation.
- metadata:
The metadata dictionary containing extra information that describes this correlation. The dictionary’s keys are all Nsstring objects . The values may be Nsstring, Nsnumber, or Nsdate objects. For a complete list of predefined metadata keys, see Metadata Keys.
Using predefined keys helps facilitate sharing data between apps; however, you are also encouraged to create custom keys as needed to extend the HealthKit sample’s capabilities.
When creating correlations representing food, always use the Hkmetadatakeyfoodtype key to provide the food’s name.
Discussion
Use a correlation object to represent composite data—that is, a sample that requires more than a single value. To create a correlation sample, first create the quantity and category samples you intend to combine into the correlation. Next, create the correlation’s type. Finally, instantiate the correlation, passing in the type, start date, end date, samples, and metadata as shown below.
Use this method when you need to include additional metadata, but the data was not recorded using external hardware. Samples representing food should always include metadata with the HKMetadataKeyFoodType key.