wrappedValue

Discussion 議論

This property behaves like the wrappedValue of a FetchRequest. In particular, SwiftUI returns the value associated with this property when you use SectionedFetchRequest as a property wrapper and then access the wrapped property by name. For example, consider the following quakes property declaration that fetches a Quake type that the Loading and Displaying a Large Data Feed sample code project defines:

@SectionedFetchRequest<String, Quake>(
    sectionIdentifier: \.day,
    sortDescriptors: [SortDescriptor(\.time, order: .reverse)]
)
private var quakes: SectionedFetchResults<String, Quake>

You access the request’s wrappedValue, which contains a SectionedFetchResults instance, by referring to the quakes property by name. That value is a collection of sections, each of which contains a group of managed objects:

Text("Found \(quakes.count) days of earthquakes")

If you need to separate the request and the result entities, you can declare quakes in two steps by using the request’s wrappedValue to obtain the results:

var fetchRequest = FetchRequest<String, Quake>(
    fetchRequest: request,
    sectionIdentifier: \.day)
var quakes: FetchedResults<String, Quake> { fetchRequest.wrappedValue }

The wrappedValue property returns an empty array when there are no fetched results; for example, because no entities satisfy the predicate, or because the data store is empty.