Android ViewModel LiveData 文档

Question

我阅读了文档，但对某些部分感到困惑。

ViewModel objects are designed to outlive specific instantiations of views or LifecycleOwners. This design also means you can write tests to cover a ViewModel more easily as it doesn't know about view and Lifecycle objects. ViewModel objects can contain LifecycleObservers, such as LiveData objects. However ViewModel objects must never observe changes to lifecycle-aware observables, such as LiveData objects. If the ViewModel needs the Application context, for example to find a system service, it can extend the AndroidViewModel class and have a constructor that receives the Application in the constructor, since Application class extends Context.

这部分让我有些困惑

However ViewModel objects must never observe changes to lifecycle-aware observables, such as LiveData objects.

指的是这种实现方式吗？

片段

class AboutFragment : Fragment() {

    private lateinit var aboutViewModel: AboutViewModel
    private var _binding: FragmentAboutBinding? = null

    // This property is only valid between onCreateView and
    // onDestroyView.
    private val binding get() = _binding!!

    override fun onCreateView(
            inflater: LayoutInflater,
            container: ViewGroup?,
            savedInstanceState: Bundle?
    ): View {
        aboutViewModel =
                ViewModelProvider(this).get(AboutViewModel::class.java)

        _binding = FragmentAboutBinding.inflate(inflater, container, false)
        val root: View = binding.root

        val textView = binding.aboutTxt

        //Observe changes
        aboutViewModel.text.observe(viewLifecycleOwner, {
            textView.text = it
        })
        return root
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }
}

视图模型

class AboutViewModel : ViewModel() {

private val _text = MutableLiveData<String>().apply {
    value = "Foobar......"
           
}

fun setText(text: String){ _text.value = text}

val text: LiveData<String> = _text

}

或者这就是他们的意思LiveData<LiveData<Object>>不要做？

Answer 1

这意味着你不应该在视图模型中的实时数据对象上使用 observe，只能在 activity/fragment 中使用，就像你已经在做的那样

Android ViewModel LiveData 文档

Android ViewModel LiveData Documentation

android

mvvm

kotlin

android-viewmodel