How to abstract FetchRequest on previews

Question

Created Jun ’20

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I would like to keep using FetchRequest for my data since I am using CoreData, however I am not sure how to apply this since in the example an object is used fore the translation of the model while FetchRequest requires a view. My first thought is to use a protocol for a view that would have the FetchRequest and do the translation then pass it up some how, but I am not sure about it. Could you provide an example on how to accomplish this, I would really appreciated it

Thanks 😊

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Answer 1

emland89 OP

Jul ’20

Ok I was able to come up with a solution, however becase of my limited knowledge with generics I ended up using AnyView instead of the actual data type which takes a hit on performance.

Code Block swiftimport SwiftUI
import PlaygroundSupport
protocol DataSourceView {
    associatedtype Data
    associatedtype Container: View
    static func make<Content: View>(@ViewBuilder content: @escaping (Data) -> Content) -> Container
}
struct SimpleData: Hashable {
    let title: String
}
struct ListView<DataSource: DataSourceView>: View where DataSource.Data == [SimpleData] {
    var body: some View {
        DataSource.make { items in
            List {
                ForEach(items, id: \.self) { item in
                    Text(item.title)
                }
            }
        }
    }
}
struct RichDataSource: DataSourceView {
    static func make<Content: View>(content: @escaping ([SimpleData]) -> Content) -> AnyView  {
        AnyView(Container(content: content))
    }
    struct Container<Content: View>: View {
        let content: ([SimpleData]) -> Content
        @State private var richDataItems = (1...10).map { $0 }
        var body: some View {
            content(richDataItems.map { SimpleData(title: "Title: \($0)") })
        }
    }
}
PlaygroundPage.current.setLiveView(ListView<RichDataSource>())

The following won't work which kind of what I would like to do. If anyone has a solution for this could you please provide an explanation, I would really appreciate it, again I have limited generics knowledge.

Code Block swiftstatic func make<Content: View>(content: @escaping ([SimpleData]) -> Content) -> Container<Content>  {
        Container(content: content)
}

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