ios 这里有什么问题：实例成员不能用于类型
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What's wrong here: Instance member cannot be used on type
提问by gurehbgui
I have the following code and I'm confused about this error message:
我有以下代码，但我对此错误消息感到困惑：
Instance member 'mydate' cannot be used on type 'TableViewController'
实例成员 'mydate' 不能用于类型 'TableViewController'
Code:
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)
]
When I write the following, I can build it but I don't know why the oder snippet is not working:
当我编写以下内容时，我可以构建它，但我不知道为什么 oder 代码段不起作用：
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)
]
回答by avismara
The problem here is that you are using selfbefore 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.
这里的问题是您self在类完全初始化之前使用。您可以拥有一个每次访问变量时都会调用的 getter，也可以懒惰地计算它。
Here is some code:
这是一些代码：
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)
]
}
}
}
Lazy computation:
懒惰计算：
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)
]
}()
}
回答by r4id4
You can use this code
您可以使用此代码
var items:Array<(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)
]
}
}
回答by Adam
The compiler gets confused because it doesn't know the type of the optional NSDate. You can let it know explicitly about the type.
编译器会感到困惑，因为它不知道 optional 的类型NSDate。你可以让它明确知道类型。
let items : Array<(Int, Int, Int, String, NSDate?)> = [
(1, 9, 7, "A", nil),
(2, 9, 7, "B", mydate),
(3, 9, 7, "C", mydate),
(4, 9, 7, "D", mydate)
]
Edit: For the problem with using instance variable, you could initialise your items with a closure.
编辑：对于使用实例变量的问题，您可以使用闭包初始化您的项目。
let items : Array<(Int, Int, Int, String, NSDate?)> = {
let mydate = NSDate()
return [
(1, 9, 7, "A", nil),
(2, 9, 7, "B", mydate),
(3, 9, 7, "C", mydate),
(4, 9, 7, "D", mydate)
]
}()
