How cast different SwiftUI View structs in a ForEach to display? - swiftui

Question

I want to display different type of View depending on what is assigned to the items.
Each relevant views conforms to this protocol:
public protocol ItemDisplayer {
init(item: ItemObject)
}
This struct stores the Item object and its associated appearance View object.
public struct ItemWithDisplay {
private let item: ItemObject
private let itemDisplayer : ItemDisplayer
public init(item : ItemObject, displayer : ItemDisplayer) {
self.item = item
self.itemDisplayer = displayer
}
public func getDisplayer() -> TimeCounterDisplayer {
return itemDisplayer
}
public func getItem() -> ItemObject {
return item
}
}
There is a few type of View which show the data some kind of way, depends on what was assigned to ItemObject.
import SwiftUI
struct OtherItemView: View, ItemDisplayer {
private var item: ItemObject
init(item: ItemObject) { self.item = item }
var body: some View { ... }
}
struct DefaultItemView: View, ItemDisplayer {
private var item: ItemObject
init(item: ItemObject) { self.item = item }
var body: some View { ... }
}
// other ItemViews ...
I'd like to seperate the items with views in the modelView class, something like this:
switch displayerType {
case .other:
self.itemWithDisplayArray.append(ItemWithDisplay(item: item, displayer: OtherItemView(itemToDisplay: item)))
case .another:
self.itemWithDisplayArray.append(ItemWithDisplay(item: item, displayer: AnotherItemView(itemToDisplay: item)))
default:
self.itemWithDisplayArray.append(ItemWithDisplay(item: item, displayer: DefaultItemView(itemToDisplay: item)))
}
This was the information required for the question below.
My question concerns the following section:
ScrollView {
ForEach(viewModel.itemWithDisplayArray, id: \.itemId) { item in
VStack {
//item.getDisplayer() as! DefaultItemView // It works
item.getDisplayer() as! AnyView // Cast from 'ItemDisplayer' to unrelated type 'AnyView' always fails // how could I fix this?
}
}
}
The cast works if the ItemDisplayer casts directly to the DefaultTimerView, or OtherItemView... but I'd like to cast to any View type.
EDIT: I've made like this in UIKit:
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let itemViewCell = collectionView.dequeueReusableCell(withReuseIdentifier: "ItemViewCell", for: indexPath) as! ItemViewCell
let itemWithDisplay = itemWithDisplayArray[indexPath.row]
itemViewCell.containerView = UIView(frame: itemViewCell.contentView.frame)
itemViewCell.containerView!.addSubview(itemWithDisplay.getDisplayer() as! UIView) // <--the POINT is here: "as! UIView"
itemViewCell.contentView.addSubview(itemViewCell.containerView!)
itemWithDisplay.display()
return itemViewCell
}
Or in Cocoa:
class ItemGridNSView : NSView {
private let itemWithDisplay : ItemWithDisplay
init(frame frameRect: NSRect, itemWithDisplay: ItemWithDisplay) {
self.itemWithDisplay = itemWithDisplay
super.init(frame:frameRect);
self.addSubview(itemWithDisplay.getDisplayer() as! NSView) // <-- Here too
itemWithDisplay.display()
}
...
I'm looking for same solution in SwiftUI.
I want to keep the independence of the domain layer from view logic, i.e. any view specific information (import SwiftUI).
I want to avoid this sorting logic in the View layer.
Could you help me please with this?
Thank you in advance for any help you can provide!

Answer 1

Make ItemDisplayer conform to View. This is so you can use it like a normal View.
public protocol ItemDisplayer: View {
init(item: ItemObject)
}
And then change ItemWithDisplay so you can use ItemDisplayer (because it now has associated type requirements):
public struct ItemWithDisplay<Displayer: ItemDisplayer> {
private let item: ItemObject
private let itemDisplayer : Displayer
public init(item : ItemObject, displayer : Displayer) {
self.item = item
self.itemDisplayer = displayer
}
public func getDisplayer() -> Displayer {
return itemDisplayer
}
public func getItem() -> ItemObject {
return item
}
}
Finally, you can now use getDisplayer() to get the view, without even needing to convert it to an AnyView:
VStack {
item.getDisplayer()
}
However, to make something an AnyView, you would do the following:
VStack {
AnyView(item.getDisplayer())
}