lateinit 属性 remindersViewModel 尚未初始化

Question

我在 activity 中使用 recyclerViews 显示两个片段。我正在尝试向回收站视图添加一个新项目，但我收到：“lateinit 属性 remindersViewModel 尚未初始化”错误。我已经在尝试在片段中初始化它。

我的片段 1：


import android.content.Intent
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.bubblereminder.room.Reminders
import com.example.bubblereminder.room.RemindersListAdapter
import com.example.bubblereminder.room.RemindersViewModel

class ScheduledFragment : Fragment() {
    private lateinit var reminderViewModel: RemindersViewModel

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

        val v = inflater.inflate(R.layout.fragment_scheduled, container, false)

        return v
    }

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

        val recyclerView = view?.findViewById<RecyclerView>(R.id.recycler_scheduled)
        val adapter = context?.let { RemindersListAdapter(it) }
        if (recyclerView != null) {
            recyclerView.adapter = adapter
        }
        if (recyclerView != null) {
            recyclerView.layoutManager = LinearLayoutManager(context)
        }

        this.reminderViewModel = ViewModelProvider(this).get(RemindersViewModel::class.java)
        reminderViewModel.allReminders.observe(viewLifecycleOwner, Observer { reminders ->
            // Update the cached copy of the words in the adapter.
            reminders?.let {
                if (adapter != null) {
                    adapter.setReminders(it)
                }
            }
        })
    }
}

我的片段 2：

    package com.example.bubblereminder

import android.content.Intent
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.bubblereminder.room.Reminders
import com.example.bubblereminder.room.RemindersListAdapter
import com.example.bubblereminder.room.RemindersViewModel

class DoneFragment : Fragment() {
    private lateinit var reminderViewModel: RemindersViewModel

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

        val v = inflater.inflate(R.layout.fragment_scheduled, container, false)

        return v
    }

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

        val recyclerView = view?.findViewById<RecyclerView>(R.id.recycler_scheduled)
        val adapter = context?.let { RemindersListAdapter(it) }
        if (recyclerView != null) {
            recyclerView.adapter = adapter
        }
        if (recyclerView != null) {
            recyclerView.layoutManager = LinearLayoutManager(context)
        }

        this.reminderViewModel = ViewModelProvider(this).get(RemindersViewModel::class.java)
        reminderViewModel.allReminders.observe(viewLifecycleOwner, Observer { reminders ->
            // Update the cached copy of the words in the adapter.
            reminders?.let {
                if (adapter != null) {
                    adapter.setReminders(it)
                }
            }
        })
    }
}

我的Activity:

    package com.example.bubblereminder

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.FrameLayout
import android.widget.Toast
import androidx.fragment.app.Fragment
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.ViewModelProviders
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.bubblereminder.room.Reminders
import com.example.bubblereminder.room.RemindersDao
import com.example.bubblereminder.room.RemindersListAdapter
import com.example.bubblereminder.room.RemindersViewModel
import com.ramotion.circlemenu.CircleMenuView

class MainActivity : AppCompatActivity() {
    private lateinit var remindersViewModel: RemindersViewModel
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        setupMenuEventListener()
        setupFragments(R.id.fragment_container1, ScheduledFragment())
        setupFragments(R.id.fragment_container2, DoneFragment())
    }

    private fun setupMenuEventListener() {
        val circleMenu = findViewById<CircleMenuView>(R.id.circle_menu)
        circleMenu.eventListener = object : CircleMenuView.EventListener() {

            override fun onButtonClickAnimationEnd(view: CircleMenuView, index: Int) {
                when (index) {
                    0 -> {
                        remindersViewModel.insert(Reminders(0,"Sample Reminder Text"))
                        val confirmToast = "Task 1 Finished"
                        Toast.makeText(this@MainActivity, confirmToast, Toast.LENGTH_SHORT)
                            .show()
                    }
                    1 -> {
                        val confirmToast = "Task 2 Finished"
                        Toast.makeText(this@MainActivity, confirmToast, Toast.LENGTH_SHORT)
                            .show()
                    }
                    2 -> {
                        val confirmToast = "Task 3 Finished"
                        Toast.makeText(this@MainActivity, confirmToast, Toast.LENGTH_SHORT)
                            .show()
                    }
                    3 -> {
                        val confirmToast = "Task 4 Finished"
                        Toast.makeText(this@MainActivity, confirmToast, Toast.LENGTH_SHORT)
                            .show()
                    }
                    4 -> {
                        val confirmToast = "Task 5 Finished"
                        Toast.makeText(this@MainActivity, confirmToast, Toast.LENGTH_SHORT)
                            .show()
                    }
                }
            }
        }
    }
    private fun setupFragments(id:Int , frag:Fragment){
        var fragmentManager = supportFragmentManager
        fragmentManager.beginTransaction()
            .replace(id, frag)
            .commit()
    }
}

我试图在 activity 中初始化视图模型，但我无法做到。

Answer 1

您拥有的每个 remindersViewModel 变量都是完全独立的，通过将它们标记为 lateinit，您承诺在尝试读取它们之前为它们设置一个值。你在片段中这样做，但在调用 insert 之前你没有初始化 MainActivity 中的片段

Answer 2

谢谢，当我在 MainActivity 的 OnCreate 中初始化它时工作：

this.remindersViewModel = ViewModelProvider(this).get(RemindersViewModel::class.java)

lateinit 属性 remindersViewModel 尚未初始化

lateinit property remindersViewModel has not been initialized

mvvm

android-fragments

kotlin

android-recyclerview

room