Question

我有这种层次结构：

class OneViewModel {
}

class OneViewController {
  var viewModel = OneViewModel()
}

class TwoViewModel : OneViewModel {
}

class TwoViewController : OneViewController {
  var viewModel = TwoViewModel() // ???
}

我知道在Swift中不允许覆盖属性类型，但是对于子ViewController携带两个ViewModel没有意义，怎么会解决这个问题呢？谢谢！

Answer 1

这应该有效

class OneViewModel {
}

class OneViewController {
    var viewModel = OneViewModel()
}

class TwoViewModel : OneViewModel {
}

class TwoViewController : OneViewController {
    override init() {
        super.init()
        self.viewModel = TwoViewModel()
    }
}

您可以将viewModel实例设置为TwoViewModel课程。

Answer 2

我用这个：

class OneViewController {
  var viewModel: OneViewModel {
    return storedViewModel
  }
  lazy var storedViewModel: OneViewModel = {
    type(of: self).viewModelProvider()
  }()
  class func viewModelProvider() -> OneViewModel {
    return OneViewModel()
  }
}

class TwoViewController {
  override var viewModel: TwoViewModel {
    return storedViewModel as! TwoViewModel
  }
  override class func viewModelProvider() -> OneViewModel {
    return TwoViewModel()
  }
}

设置有点冗长，但之后使用起来很简单明了。

使用MVVM时，如何在子ViewControllers中扩展ViewModel？

2 个答案: