Type '() -> ()' cannot conform to 'View'; only struct/enum/class types can conform to protocols

Question

I'm running a function in order to populate a list of expenses. I need to run the function to populate the list using .onAppear(perform: fetchRows) so that the list updates as soon as the the view appears.

Xcode doesn't like the fact that I'm running a function to populate expensesList. How can I make this work? Is there a better way of going about this?

@State var expensesList: [ExpensesList]?

var body: some View {
    
    NavigationView{
        VStack{
                
                if expensesList != nil{
                    
                    
                    List{
                        
                        ForEach(self.expensesList!) {   <-- Type '() -> ()' cannot conform to 'View'; only struct/enum/class types can conform to protocols
                            (log: ExpensesList) in {
                                Button(action: {
                                    self.editExpense = log
                                })
                            
                            ExpenseRow(name: log.expense, date: log.date, amount: log.cost, account: log.account)
                            }
                        }.onDelete(perform: onDelete)
                    }
                }
            }.navigationTitle("Expense List")

struct ExpensesList: Identifiable, Equatable {
    let id: UUID
    let expense: String
    let cost: Double
    let account: String
    let date: Date
}

func fetchRows(){
    Expenses.fetchAllExpensesInDateRange(context: self.context) { (results) in
        guard !results.isEmpty else { return }
        
        self.expensesList = results.map({ (result) -> ExpensesList in
            print(result.id,result.expenseName,result.expenseCost, result.expenseAccount, result.expenseDate)
            return ExpensesList(id: result.id, expense: result.expenseName, cost: result.expenseCost, account: result.expenseAccount, date: result.expenseDate)
        })
    }
}

The sheet I use to edit expenses is here. As you can see I use a Core Data entity called Expenses to store my expense objects.

                .sheet(item: $editExpense, onDismiss: {
                    self.editExpense = nil
                })
                {
                    (log: Expenses) in
                    ExpenseDetail(
                        context: self.context,
                        editExpense: log,
                        name: log.expenseName ?? "",
                        amount: String(log.expenseCost),
                        category: log.expenseCategory ?? "",
                        date: log.expenseDate ?? Date(),
                        account: log.expenseAccount ?? "",
                        isMonthly: log.expenseIsMonthly
                    ).environment(\.managedObjectContext, self.context)
                    
                    
                    
                }

pawello2222 pawello2222 · Accepted Answer · 2020-10-22T19:20:09

You have an extra { after (log: ExpensesList) in { and your Button has no content parameter.

Try the following instead (I assume that ExpenseRow should be the content of the Button):

ForEach(self.expensesList!) { log in
    Button(action: {
        self.editExpense = log
    }) {
        ExpenseRow(name: log.expense, date: log.date, amount: log.cost, account: log.account)
    }
}

Note that in SwiftUI 2 you can use control flow statements (like if-let) directly in @ViewBuilder blocks:

if let expensesList = expensesList {
    List {
        ForEach(expensesList) { log in
            // ...
        }
    }
}

Type '() -> ()' cannot conform to 'View'; only struct/enum/class types can conform to protocols

1 Answers