Require a SwitftUI View in a protocol without boilerplate - swift

Question

[ Ed: Once I had worked this out, I edited the title of this question to better reflect what I actually needed. - it wasn't until I answered my own question that I clarified what I needed :-) ]
I am developing an App using SwiftUI on IOS in which I have 6 situations where I will have a List of items which I can select and in all cases the action will be to move to a screen showing that Item.
I am a keen "DRY" advocate so rather than write the List Code 6 times I want to abstract away the list and select code and for each of the 6 scenarios I want to just provide what is unique to that instance.
I want to use a protocol but want to keep boilerplate to a minimum.
My protocol and associated support is this:
import SwiftUI
/// -----------------------------------------------------------------
/// ListAndSelect
/// -----------------------------------------------------------------
protocol ListAndSelectItem: Identifiable {
var name: String { get set }
var value: Int { get set }
// For listView:
static var listTitle: String { get }
associatedtype ItemListView: View
func itemListView() -> ItemListView
// For detailView:
var detailTitle: String { get }
associatedtype DetailView: View
func detailView() -> DetailView
}
extension Array where Element: ListAndSelectItem {
func listAndSelect() -> some View {
return ListView(items: self, itemName: Element.listTitle)
}
}
struct ListView<Item: ListAndSelectItem>: View {
var items: [Item]
var itemName: String
var body: some View {
NavigationView {
List(items) { item in
NavigationLink(
destination: DetailView(item: item, index: String(item.value))
) {
VStack(alignment: .leading){
item.itemListView()
.font(.system(size: 15)) // Feasible that we should remove this
}
}
}
.navigationBarTitle(Text(itemName).foregroundColor(Color.black))
}
}
}
struct DetailView<Item: ListAndSelectItem>: View {
#Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>
var item: Item
var index: String
var body: some View {
NavigationView(){
item.detailView()
}
.navigationBarTitle(Text(item.name).foregroundColor(Color.black))
.navigationBarItems(leading: Button(action: {
self.presentationMode.wrappedValue.dismiss()
}, label: { Text("<").foregroundColor(Color.black)}))
}
}
which means I can then just write:
struct Person: ListAndSelectItem {
var id = UUID()
var name: String
var value: Int
typealias ItemListView = PersonListView
static var listTitle = "People"
func itemListView() -> PersonListView {
PersonListView(person: self)
}
typealias DetailView = PersonDetailView
let detailTitle = "Detail Title"
func detailView() -> DetailView {
PersonDetailView(person: self)
}
}
struct PersonListView: View {
var person: Person
var body: some View {
Text("List View for \(person.name)")
}
}
struct PersonDetailView: View {
var person: Person
var body: some View {
Text("Detail View for \(person.name)")
}
}
struct ContentView: View {
let persons: [Person] = [
Person(name: "Jane", value: 1),
Person(name: "John", value: 2),
Person(name: "Jemima", value: 3),
]
var body: some View {
persons.listAndSelect()
}
}
which isn't bad but I feel I ought to be able to go further.
Having to write:
typealias ItemListView = PersonListView
static var listTitle = "People"
func itemListView() -> PersonListView {
PersonListView(person: self)
}
with
struct PersonListView: View {
var person: Person
var body: some View {
Text("List View for \(person.name)")
}
}
still seems cumbersome to me.
In each of my 6 cases I'd be writing very similar code.
I feel like I ought to be able to just write:
static var listTitle = "People"
func itemListView() = {
Text("List View for \(name)")
}
}
because that's the unique bit.
But that certainly won't compile.
And then the same for the Detail.
I can't get my head around how to simplify further.
Any ideas welcome?

Answer 1

The key to this is, if you want to use a view in a protocol then:
1) In the protocol:
associatedtype SpecialView: View
var specialView: SpecialView { get }
2) In the struct using the protocol:
var specialView: some View { Text("Special View") }
So in the situation of the question:
By changing my protocol to:
protocol ListAndSelectItem: Identifiable {
var name: String { get set }
var value: Int { get set }
// For listView:
static var listTitle: String { get }
associatedtype ListView: View
var listView: ListView { get }
// For detailView:
var detailTitle: String { get }
associatedtype DetailView: View
var detailView: DetailView { get }
}
I can now define Person as:
struct Person: ListAndSelectItem {
var id = UUID()
var name: String
var value: Int
static var listTitle = "People"
var listView: some View { Text("List View for \(name)") }
var detailTitle = "Person"
var detailView: some View { Text("Detail View for \(name)") }
}
which is suitable DRY and free of boilerplate!