我在一个片段中有一个TextView。使用LiveData，我可以更改片段中的文本。通过使用MainActivity（片段外）中的按钮，我试图更改TextView中的文本，但它不起作用。有人能帮助我吗？下面是我的代码：
这是具有按钮和片段的MainActivity

class MainActivity : AppCompatActivity() {
    var tg: ToneGenerator? = null
    private lateinit var btn: Button
    private lateinit var viewModel:ViewModel

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

        tg = ToneGenerator(AudioManager.STREAM_SYSTEM, 100)

        btn = findViewById(R.id.buttonTest1)

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

        btn.setOnClickListener {
            tg?.startTone(ToneGenerator.TONE_PROP_BEEP)
            viewModel.changeMLD()
        }
    }
}

这是具有TextView的片段

class Fragment : Fragment() {

    private lateinit var txt1: TextView
    public lateinit var viewModel:ViewModel

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

    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

        // Inflate the layout for this fragment
        val view: View = inflater.inflate(R.layout.fragment, container, false)

        txt1 = view.findViewById(R.id.txt1)

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

        viewModel.initiateMLD()

        viewModel.LD.observe(viewLifecycleOwner, Observer {
            txt1.setText("Count is "+it)
        })

        return view
    }

}

这是包含LiveData的ViewModel

class ViewModel : ViewModel(){
    private var clickCount:Int = 0

    private var MLD = MutableLiveData<Int>()
    var LD : LiveData<Int> = getMLD()             // observer watches this variable

    fun initiateMLD(){
        MLD.value = 5
        clickCount = 5
    }

    fun getMLD():MutableLiveData<Int>{
        return MLD
    }

    fun changeMLD(){
        clickCount+=2
        MLD.value = clickCount
    }
}