共享的livedata观察器不能在片段和活动之间工作

class SharedViewModel : ViewModel() {
    private val _liveData = MutableLiveData<String>()
    val liveData: LiveData<String> get() = _liveData

    fun updateData(data: String) {
        _liveData.value = data
    }
}

class MainActivity : AppCompatActivity() {
    private lateinit var viewModel: SharedViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        viewModel = ViewModelProvider(this).get(SharedViewModel::class.java)

        // 更新 LiveData
        viewModel.updateData("Hello from Activity")
    }
}

class MyFragment : Fragment() {
    private lateinit var viewModel: SharedViewModel

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        viewModel = ViewModelProvider(requireActivity()).get(SharedViewModel::class.java)

        // 观察 LiveData
        viewModel.liveData.observe(viewLifecycleOwner, Observer { data ->
            // 更新 UI
            textView.text = data
        })
    }
}