无法从活动中观察viewmodel中的livedata集

Question

我是一个新的Android开发人员，我正试图观察ViewModel中的布尔集。当应用程序启动时，我可以观察到它的初始状态，但以后应用的任何更改似乎都不会触发观察者（即当我切换片段时）。

下面是我的ViewModel的代码：

class MyMusicViewModel  : ViewModel() {


    private var _MyMusicViewOn = MutableLiveData<Boolean>()
    val MyMusicViewOn: LiveData<Boolean> get() = _MyMusicViewOn



    init {
        Timber.i("MyMusicViewModel Init Called!")
        setMyMusicView(true)
    }

    override fun onCleared() {
        super.onCleared()
        Timber.i("MyMusicViewModel Cleared!")
        setMyMusicView(false)
    }


    fun setMyMusicView(setter: Boolean) {
        Timber.i("MyMusicViewModel setter called! %s", setter)
        _MyMusicViewOn.value = setter
    }


}

class FullscreenActivity : AppCompatActivity() {


    private val viewModel: MyMusicViewModel by viewModels()

  
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

       
        viewModel.MyMusicViewOn.observe(this, Observer { MyMusicViewOn ->
            Timber.i("Observer called for MyMusicViewOn %s", MyMusicViewOn)
        })

    }

}

class MyMusicFragment : Fragment() {

    private lateinit var viewModel: MyMusicViewModel

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        val binding = DataBindingUtil.inflate<FragmentMyMusicBinding>(
            inflater,
            R.layout.fragment_my_music,
            container,
            false
        )
        
        viewModel = ViewModelProvider(this).get(MyMusicViewModel::class.java)

        return binding.root
    }
    

    override fun onResume() {
        super.onResume()

        Timber.i("MyMusicViewFragment resumed!")
        viewModel.setMyMusicView(true)

    }




}

万事如意，

晶圆厂。

Answer 1

我猜想，无论您在片段中填充ViewModel属性，您都没有使用活动的ViewModel实例。获取活动正在使用的相同实例的最简单方法是使用ActivityViewModels委托：

private val viewModel: MyMusicViewModel by activityViewModels()