projectedValue

Discussion 議論

SwiftUI returns the value associated with this property when you use FetchRequest as a property wrapper on a FetchedResults instance, and then access the results with a dollar sign ($) prefix. The value that SwiftUI returns is a Binding to the request’s FetchRequest.Configuration structure, which dynamically configures the request.

For example, consider the following fetch request for a type that the Loading and Displaying a Large Data Feed sample code project defines to store earthquake data, sorted based on the time property:

@FetchRequest(sortDescriptors: [SortDescriptor(\.time, order: .reverse)])
private var quakes: FetchedResults<Quake>

You can use the projected value to enable a Table instance to make updates:

Table(quakes, sortOrder: $quakes.sortDescriptors) {
    TableColumn("Place", value: \.place)
    TableColumn("Time", value: \.time) { quake in
        Text(quake.time, style: .time)
    }
}

Because you initialize the table using a binding to the descriptors, the table can modify the sort in response to actions that the user takes, like clicking a column header.