当 Fragment 中的数据发生更改时，主 Activity 中未触发 LiveData Observer

Question

更改字符串数据时，我的 MainActivity 中的观察者没有被触发

这是我的 主要活动：

package com.example.translator

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.text.Editable
import android.text.TextWatcher
import android.util.Log

import android.widget.EditText
import android.widget.TextView
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import com.example.translator.databinding.ActivityMainBinding;
import com.example.translator.databinding.FragmentTranslateBinding
import com.example.translator.viewmodellivedata.TranslateViewModel

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private lateinit var viewModel: TranslateViewModel


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding =ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        binding.translateText.text = "translation.."



        viewModel = ViewModelProvider(this).get(TranslateViewModel::class.java)
        viewModel.currentWord().observe(this, Observer {
            binding.translateText.text = it.toString()
            Log.d("current", it.toString())
        })




    }



}

翻译ViewModel：

package com.example.translator.viewmodellivedata

import androidx.lifecycle.MutableLiveData
import androidx.lifecycle.ViewModel
import androidx.lifecycle.LiveData

class TranslateViewModel : ViewModel() {
    private var _currentWord = MutableLiveData<String>()


    fun currentWord(): LiveData<String> {
        return _currentWord
    }

    fun setCurrentWord(word: String) {
        _currentWord.value = word
    }




}

翻译片段：

package com.example.translator

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.text.TextWatcher
import android.text.Editable
import android.view.View
import android.view.ViewGroup
import android.util.Log
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import com.example.translator.databinding.FragmentTranslateBinding
import com.example.translator.viewmodellivedata.TranslateViewModel


// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"

/**
 * A simple [Fragment] subclass.
 * Use the [translateFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class translateFragment : Fragment() {
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null
    private var _binding: FragmentTranslateBinding? = null  // View Binding instance
    private val binding get() = _binding!!
    private lateinit var  viewModel: TranslateViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        _binding = FragmentTranslateBinding.inflate(inflater, container, false)
        val view = binding.root

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


        binding.editText.hint = "Write something..."





        // Add a TextWatcher to the EditText
        binding.editText.addTextChangedListener(object : TextWatcher {
            override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
                // This method is called before text is changed
            }

            override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
                // This method is called as text is changing
            }

            override fun afterTextChanged(s: Editable?) {
                // This method is called after text has changed
                val enteredText = s.toString()
                //binding.editText.setText(enteredText)
                //binding.translateText.text

                viewModel.setCurrentWord(enteredText)
                //viewModel.currentWord().observe(viewLifecycleOwner, Observer { word ->
                //    // This code will execute when the LiveData value changes
                ///    Log.d("current", word.toString())
               // })






                // Reattach the TextWatcher



                // You can perform translation or any other actions here with the enteredText
            }
        })


            //val view = binding.root

        //viewModel = ViewModelProvider(this).get(TranslateViewModel::class.java)
        return view
    }
    override fun onDestroyView() {
        super.onDestroyView()
        _binding = nul
l
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment translateFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            translateFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }

我试图让

TextView

使用实时数据观察器显示用户在片段

editview

中输入的内容，但每次我在

edittext

中输入内容时，文本视图都会对其做出反应，而观察者并没有被在我的 MainActivity 中触发

Answer 1

在 Fragment 内部，您需要将

requireActivity()

传递给 ViewModelProvider 构造函数，而不是传递

this

。您传递的参数是 ViewModel 将加载的范围，因此如果它们不匹配，它们将是不同的实例。

顺便说一句，使用

by viewModels()

和片段中的

by activityViewModels()

比愚弄视图模型提供者要容易得多。