ViewModel、LiveData 的问题

Question

我有主片段和对话框片段。在“开始”中，我进入带有城市列表的 dialogFragment，并获取一个用于保存在 LiveData

中

listOfCities.setOnItemClickListener { parent, view, position, id ->
            homeViewModel.selectCityTo((listOfCities.getItemAtPosition(position) as HashMap<String, String>).getValue("name"))
            Log.e("Search", homeViewModel.cityTo.value)
}

我检查了 Logcat 及其工作。但是当我回到主片段时，Livedata 是空的。 TextView(cityTo) 没有变化

 homeViewModel = ViewModelProvider(this).get(HomeViewModel::class.java)
        val root = inflater.inflate(R.layout.fragment_home, container, false)
        val cityFrom = root.findViewById<TextView>(R.id.cityFrom)
        val cityTo = root.findViewById<TextView>(R.id.cityTo)
        homeViewModel.cityFrom.observe(viewLifecycleOwner, Observer {
            cityFrom.text = it
        })
        homeViewModel.cityTo.observe(viewLifecycleOwner, Observer {
            cityTo.text = it
        })

视图模型

class HomeViewModel : ViewModel() {

    private val _cityFrom = MutableLiveData<String>()
    private val _cityTo = MutableLiveData<String>()

    val cityFrom: LiveData<String> = _cityFrom
    val cityTo: LiveData<String> = _cityTo

    fun selectCityTo(to: String){
        _cityTo.value = to
        Log.e("hViewModel", "${cityTo.value}")

    }
    fun selectCityFrom(from: String){
        _cityFrom.value = from
    }
}

Answer 1

您应该将 activity 传递给 ViewModelProvider（在您创建视图模型的两个片段中）：

ViewModelProvider(requireActivity()).get(HomeViewModel::class.java)

如果你传递Fragment，你会在每个Fragment中获得不同的ViewModel。

ViewModel、LiveData 的问题

Trouble with ViewModel, LiveData

android

kotlin

android-livedata

android-viewmodel

mutablelivedata