How to bind to property of property of binding in swiftui?

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Created Dec ’23

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I have a SwiftData object called Asset. Asset has an optional relationship to another SwiftData object called Income. Income has an Int? called cashflow.

AssetsListView shows a list of assets and has a + button to create an asset object and show the AddEditAssetView where the user can fill in the values on the asset.

The newly added asset is a @State variable in AssetsListView.

That asset is a @Binding in AddEditAssetView.

In AddEditAssetView, I use a custom view called MoneyTextField which is just a simple wrapper around a standard TextField but it does some customized formatting and such.

One of these MoneyTextFields that I'm showing is so the user can edit the cashflow amount which is found in $asset.income.cashflow.

MoneyTextField("placeholder text", value: $asset.income.cashflow)
// inside MoneyTextField, value is: @Binding var value: Int?

But since all relationships in SwiftData need to be optional, $asset.income is a Income? and so I get the understandable error:

Value of optional type 'Income?' must be unwrapped to refer to member 'cashflow' of wrapped base type 'Income'

But if I change it to:

MoneyTextField("placeholder text", value: $asset.income?.cashflow)

I get the error:

Cannot use optional chaining on non-optional value of type 'Binding<Income?>'

When $asset is my @Binding, how do I pass $mybinding.property.otherproperty as a binding to a subview?

I'm a long time ObjC app dev, new-ish to swift and brand new to swiftui, so I'm kind of lost. Is there a simple way to do what I'm doing or is my entire approach wrong because I'm not thinking in a proper swiftui mind yet?

More code for context:

struct AssetsView: View {

    @State var addedasset: Asset?
    // more stuff
    
    var body: some View {
    	NavigationStack {
            List {
            	MoreStuff()
            }
            .toolbar {
                ToolbarItem {
                    Button {
                        let asset = Asset(name: "", assetType: .realestate)
                        self.addedasset = asset
                        self.modelContext.insert(asset)
                    } label: {
                        Image(systemName: "plus")
                    }
                    .fullScreenCover(isPresented: $showingaddscreen) {
                        AddEditAssetView(player: $player, asset: $addedasset)
                    }
                }
            }
        }
    }
}


struct AddEditAssetView: View {
	@Binding var asset: Asset
	
	var body: some View {
        NavigationStack {
            Form {
            	OtherStuff()
            	
            	// here's where the compile error is
            	MoneyTextField(localizedstringkey: "realestate_cashflow_eg", value: $asset.income?.cashflow)
            }
        }
    }
}


struct MoneyTextField: View {
    var localizedstringkey: LocalizedStringKey
    
    @Binding var value: Int?
    
    @State var valuestring = ""
    
    var body: some View {
        TextField(localizedstringkey, text: $valuestring)
            .textFieldStyle(.roundedBorder)
            .keyboardType(.numberPad)
            .onReceive(Just(valuestring), perform: { foo in
                print("onReceive: foo | \(String(describing: foo))")
                updatevalueint(valstring: foo)
            })
            .onAppear {
                if let intval = self.value {
                    updatevaluestring(val: intval)
                }
            }
    }
}

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