arrays - 显示核心数据库中 PickerView 的值

Question

我是一名新的 IOS 开发人员。我正在使用 Xcode 8 和 swift 3。我想将核心数据库中保存的数据的值显示到 pickerView 中。我的下面的代码有一个错误( fatal error :索引超出范围)

我定义一个数组来保存从核心数据库获取的数据

  var boundName  = [String]()
  var expenses = [NSManagedObject]()// variable to fetch the data from core database
  var num = 0// variable to hold the count of the fetched data

这是pickerView的函数

public func numberOfComponents(in pickerView: UIPickerView) -> Int {
    return 1;
}

func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {

    let request = NSFetchRequest <NSFetchRequestResult> (entityName : "ExpenseBound_Table")
    request.returnsObjectsAsFaults = false


    do {
        expenses = try self.context.fetch(request) as! [NSManagedObject]
       num = expenses.count

    } catch { print(error) }

    return num;
}

func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {


    let request = NSFetchRequest <NSFetchRequestResult> (entityName : "ExpenseBound_Table")
    request.returnsObjectsAsFaults = false

    do{
    expenses = try self.context.fetch(request) as! [NSManagedObject]

        if expenses.count > 0 {


              let person = expenses[row] 
               let boundText = person.value(forKey: "boundName_Expense" ) as? String
              boundName [row] = boundText! //error fires here fatal error: Index out of range




        }

    }
    catch{
        print ("Fetch Faield")
    }
    return boundName[row]
}

Answer 1

数组使用以下方式声明:

var boundName = [String]()

这种方式的声明不会指定数组的大小，因此当您运行以下行时，它将崩溃:

boundName [row] = boundText!

解决方案:

使用append代替:

boundName.append(boundText!)