How to declare a generic view

Question

Created Jul ’20

Replies 2

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I'm trying to build a menu using the code below. I've run into some difficulty declaring the destination view in the struct.

I get the error: Protocol 'View' can only be used as a generic constraint because it has Self or associated type requirements

The designation of course will be the a view in the app.
Any help would be greatly appreciated.

Code Block import SwiftUI
struct MenuList: Identifiable {
		var id: Int
		var image: String
		var name: String
		var destination: View // This line is where the problem is
}
extension MenuList {
		static func getMenu() -> [MenuList] {
				return[
						MenuList(id: 1, image: "house", name: "Welcome", destination: Welcome_View()),
						MenuList(id: 2, image: "text.justify", name: "MW List", destination: TrickList_View()),
						MenuList(id: 3, image: "list.bullet", name: "My Collection", destination: MyCollection_View()),
						MenuList(id: 4, image: "text.badge.plus", name: "Telly Sheet", destination: Tally_View()),
						MenuList(id: 5, image: "rectangle.and.paperclip", name: "Want List", destination: WantList_View()),
						MenuList(id: 6, image: "gear", name: "Settings", destination: Settings_View()),
						MenuList(id: 7, image: "arrowshape.turn.up.right", name: "Share", destination: Share_View()),
						MenuList(id: 8, image: "questionmark.circle.fill", name: "Help", destination: Help_View()),
						MenuList(id: 9, image: "photo.on.rectangle", name: "Presentation", destination: Presentation_View())]
		}
}

Answered by OOPer in 618232022

You can make your MenuList generic in this way.

Code Block struct MenuList<TheView: View>: Identifiable {
    var id: Int
    var image: String
    var name: String
    var destination: TheView
}

(By the way, each MenuList represents an item in a menu, not a list...)

But this cannot be the solution for your issue. You cannot declare an Array of non-specialized generic type in Swift.
(And Xcode 11 shows weird messages when you use the generic MenuList above.

Code Block Cannot convert value of type 'Welcome_View' to expected argument type 'TheView'

With the wrong Fix-it suggestion:

Code Block Insert 'as! TheView'

Never tap the Fix button, which never fixes.)

Maybe using AnyView is the easiest solution for your issue.

Code Block struct MenuItem: Identifiable {
    var id: Int
    var image: String
    var name: String
    var destination: AnyView
}
extension MenuItem {
    init<TheView: View>(id: Int, image: String, name: String, destination: TheView) {
        self.id = id
        self.image = image
        self.name = name
        self.destination = AnyView(destination)
    }
}
extension MenuItem {
    static func getMenu() -> [MenuItem] {
        return[
            MenuItem(id: 1, image: "house", name: "Welcome", destination: Welcome_View()),
            MenuItem(id: 2, image: "text.justify", name: "MW List", destination: TrickList_View()),
            MenuItem(id: 3, image: "list.bullet", name: "My Collection", destination: MyCollection_View()),
						//...
				]
    }
}

But having Views inside non-View data types may cause some unexpected behavior and you may need to fix that in the near future.

Boost

Answer 1

OOPer OP

Jul ’20

Accepted Answer

You can make your MenuList generic in this way.

Code Block struct MenuList<TheView: View>: Identifiable {
    var id: Int
    var image: String
    var name: String
    var destination: TheView
}

(By the way, each MenuList represents an item in a menu, not a list...)

But this cannot be the solution for your issue. You cannot declare an Array of non-specialized generic type in Swift.
(And Xcode 11 shows weird messages when you use the generic MenuList above.

Code Block Cannot convert value of type 'Welcome_View' to expected argument type 'TheView'

With the wrong Fix-it suggestion:

Code Block Insert 'as! TheView'

Never tap the Fix button, which never fixes.)

Maybe using AnyView is the easiest solution for your issue.

Code Block struct MenuItem: Identifiable {
    var id: Int
    var image: String
    var name: String
    var destination: AnyView
}
extension MenuItem {
    init<TheView: View>(id: Int, image: String, name: String, destination: TheView) {
        self.id = id
        self.image = image
        self.name = name
        self.destination = AnyView(destination)
    }
}
extension MenuItem {
    static func getMenu() -> [MenuItem] {
        return[
            MenuItem(id: 1, image: "house", name: "Welcome", destination: Welcome_View()),
            MenuItem(id: 2, image: "text.justify", name: "MW List", destination: TrickList_View()),
            MenuItem(id: 3, image: "list.bullet", name: "My Collection", destination: MyCollection_View()),
						//...
				]
    }
}

But having Views inside non-View data types may cause some unexpected behavior and you may need to fix that in the near future.

1

Answer 2

quailcreek OP

Jul ’20

Thanks.
I did tried AnyView but the secondary extension was what was needed.

0