无法分配属性：'item'是'let'常量（Swift 4）

Question

我正在尝试在我用来处理调用的函数中创建一个循环但是我收到错误“无法分配给属性：'item'是'let'常量”

 func didReceiveResponse(response:NearbyCars?, error : Error?) -> Void {
        dount += 1
        if let error = error {
            let alertController = UIAlertController(title: "Error", message: error.localizedDescription, preferredStyle: .alert)
            let actionDismiss = UIAlertAction(title: "Dismiss", style: .cancel, handler: nil)
            let actionRetry = UIAlertAction(title: "Retry", style: .default, handler: { (action) in
                DispatchQueue.main.async {
                    self.loadPlaces(true)

                }
            })
            alertController.addAction(actionRetry)
            alertController.addAction(actionDismiss)
            DispatchQueue.main.async {
                self.present(viewController: alertController)

            }
        }
        if let response = response {

        self.response = response
        if response.status == "OK" {
            if let carsDownloaded = response.cars {
                 var number = numberCars / (categories?.count)!
                let quotient = numberCars / (categories?.count)!
                let remainder = numberCars % (categories?.count)!

                for item in (categories?.enumerated())! {
                    item.element?.availability = quotient + (item.offset < remainder ? 1 : 0)
                }      // HERE THE ERROR



            cars.append(contentsOf: carsDownloaded.prefix(number))

        if dount == numberCars { return }
        sortedArray = cars.sorted {
            distance(from: currentLocation!, to: $0.location!) < distance(from: currentLocation!, to: $1.location!)

        }
    }


             self.tableView?.reloadData()
           } else {
                let alert = UIAlertController.init(title: "Error", message: response.status, preferredStyle: .alert)
                alert.addAction(UIAlertAction.init(title: "Cancel", style: .cancel, handler: nil))
                alert.addAction(UIAlertAction.init(title: "Retry", style: .default, handler: { (action) in
                    DispatchQueue.main.async {
                        self.loadPlaces(true)

                    }
                }))
                 self.present(viewController: alert)
             }
            isLoading = false

        } else {
            print("response is nil")
        }
    }

在这条线item.element?.availability = quotient + (item.offset < remainder ? 1 : 0)，而我正在尝试创建一个循环，将其余的numberCars / (categories?.count)!分配到类别（因为现在var number = numberCars / (categories?.count)!工作只有没有休息）。我该如何解决？

Answer 1

您可以在一个范围内执行循环，然后通过索引访问categories以获取可变对象：

for i in 0..<(categories?.count)! {
    var item = categories[i]
    item.element?.availability = quotient + (item.offset < remainder ? 1 : 0)
} 

我还建议通过在categories附近守卫来避免使用武力展开：

guard let categories = categories else {
   //Handle a nil categories array here
   return
}