尝试分配新值时,编译器会抛出错误：
Cannot assign to immutable expression of type 'Bool?'
我上课了：
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]].
如何使变量选择为可变？
(我希望这不是一个重复的问题,我发现了许多类似的问题,但无法解决这个问题.)
(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
