使用viewModels从ChildFragment访问ParentFragment中的ViewModel [英] Accessing ViewModel in ParentFragment from ChildFragment using viewModels

问题描述

我正在尝试使用viewModels从ChildFragment访问ParentFragment的ParentViewModel.这是我的代码.

I am trying to access the ParentViewModel for ParentFragment from ChildFragment using viewModels. This is my code.

// In ParentFragment

class ParentFragment : Fragment() {
    val parentViewModel: ParentViewModel by viewModels {
        ParentViewModelFactory(getRepository())
    }
    ...
}

// In ChildFragment

class ChildFragment : Fragment() {
    val parentViewModel: ParentViewModel by viewModels(
        { requireParentFragment() }
    )
    ...
}

但是，仅当我在ParentViewModel中设置LiveData变量并使ParentFragment如此观察时，此代码才有效:

However, this code only works when I setup a LiveData variable in ParentViewModel and have ParentFragment observe it like so:

parentViewModel.text.observe(this) {
    toast(it)
}

我没有必要从ParentFragment内部观察ViewModel.我只需要它为ChildFragments定义lifecycle.

I have no use for observing the ViewModel from inside ParentFragment. I only need it to define the lifecycle for the ChildFragments.

如果我摆脱上面的观察，就会收到此错误:

If I get rid of the observation above I get this error:

'java.lang.RuntimeException:无法创建类ParentViewModel的实例'

'java.lang.RuntimeException: Cannot create an instance of class ParentViewModel'

如何让ChildFragments访问ParentViewModel而不设置虚拟活动数据对象，以便ParentFragment可以观察它们.

How can I have the ChildFragments access the ParentViewModel without setting up dummy live data objects so as the ParentFragment can observe them.

推荐答案

在ChildFragment中，您应该在初始化时传递工厂.试试这个

In ChildFragment you should pass factory when init it. Try this

class ChildFragment : Fragment() {
    val parentViewModel: ParentViewModel by viewModels(
        { requireParentFragment() }
    ) { ParentViewModelFactory(getRepository()) }
    ...
}

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