ios - 初始化前使用的变量

Question

我有问题

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    let destViewController = segue.destinationViewController as! SecondTableViewController
    var secondArrays :  SecondTableData

    if let indexPath = self.tableView.indexPathForSelectedRow {
        secondArrays = secondArrayData[indexPath.row]
    }
    destViewController.secondArray = secondArrays.secondTitle    
}

我的行有错误

destViewController.secondArray = secondArrays.secondTitle

secondArrays used before being initialized

为什么我会收到这个错误？请帮助，只是 Swift 的新手。时间差

Answer 1

这是因为在 Swift 中初始化变量的方式，在 Swift Class 中每个属性在使用之前都需要一些默认值。

Class initialisation in Swift is a two-phase process. In the first phase, each stored property is assigned an initial value by the class that introduced it. Once the initial state for every stored property has been determined, the second phase begins, and each class is given the opportunity to customize its stored properties further before the new instance is considered ready for use.

尝试如下更改您的代码:

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
  let destViewController = segue.destinationViewController as! SecondTableViewController
  var secondArrays :  SecondTableData?

  if let indexPath = self.tableView.indexPathForSelectedRow {
    secondArrays = secondArrayData[indexPath.row]

    //Here you're making sure that the secondArrays would must have a value
    destViewController.secondArray = secondArrays.secondTitle
  }

}