尝试分配新值时,编译器会抛出错误:
Cannot assign to immutable expression of type 'Bool?'
我有一个班级:
class Setting {
struct Item {
var text: String
var selected: Bool?
init(withText text: String) {
self.text = text
self.selected = nil
}
var items: Any
init(items:Any) {
self.items = items
}
}
在prepareForSegue
中的源视图控制器中:
let item = Setting.Item(withText: user.description)
let setting = Setting(items: [item])
destinationViewController.setting = setting
在目标视图控制器中:
class DestinationViewController: UITableViewController {
var setting: Setting!
override func viewDidLoad() {
super.viewDidLoad()
//this works
_ = (setting.items as! [Setting.Item])[index].selected
// this throws the error
(setting.items as! [Setting.Item])[index].selected = false
}
}
我将项目声明为Any,因为它可以包含[Items]或[[Items]]。
如何使变量selected
可变?
(我希望这不是一个重复的问题,我发现了很多类似的问题,但无法解决这个问题。)
答案 0 :(得分:12)
(setting.items as! [Setting.Item])
返回一个不可变的值。你不能在它上面执行变异功能。然而,你可以做什么,把它放在一个临时变量中,改变它,并将它分配回你的财产:
var temporaryVariable = (setting.items as! [Setting.Item])
temporaryVariable[index].selected = false
setting.items = temporaryVariable