这里有什么问题：实例成员不能用于类型 [英] What's wrong here: Instance member cannot be used on type

问题描述

我有以下代码，我对此错误消息感到困惑：

I have the following code and I'm confused about this error message:

实例成员'mydate'不能用于类型'TableViewController'

Instance member 'mydate' cannot be used on type 'TableViewController'

代码：

class TableViewController: UITableViewController {    
    let mydate = NSDate()
    let items = [
        (1, 9, 7, "A", mydate),
        (2, 9, 7, "B", mydate),
        (3, 9, 7, "C", mydate),
        (4, 9, 7, "D", mydate)
    ]

当我写下以下内容时，我可以构建它，但我不知道为什么oder代码片段不工作：

When I write the following, I can build it but I don't know why the oder snippet is not working:

class TableViewController: UITableViewController {    
    let mydate = NSDate()
    let items = [
        (1, 9, 7, "A", nil),
        (2, 9, 7, "B", mydate),
        (3, 9, 7, "C", mydate),
        (4, 9, 7, "D", mydate)
    ]

推荐答案

这里的问题是你在完全初始化类之前使用 self 。您可以拥有一个getter，每次访问变量时都会调用它，或者懒惰地计算它。

The problem here is that you are using self before the class is fully initialised. You can either have a getter which will be called every time you access the variable or compute it lazily.

以下是一些代码：

class TableViewController: UITableViewController {
    let mydate = NSDate()
    var items : [(Int,Int,Int,String,NSDate)] {
        get {
            return [
                (1, 9, 7, "A", mydate),
                (2, 9, 7, "B", mydate),
                (3, 9, 7, "C", mydate),
                (4, 9, 7, "D", mydate)
            ]

        }
    }
}

延迟计算：

class TableViewController: UITableViewController {
    let mydate = NSDate()
    lazy var items : [(Int,Int,Int,String,NSDate)] =  {

            return [
                (1, 9, 7, "A", self.mydate),
                (2, 9, 7, "B", self.mydate),
                (3, 9, 7, "C", self.mydate),
                (4, 9, 7, "D", self.mydate)
            ]


    }()
}

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