在Android Kotlin中实现底部导航栏时出错

我是android开发的新手。 我尝试在我的应用程序中实现导航栏，从片段A切换到片段B。 在片段A中有一个浮动操作按钮，它指向片段c。 我通过导航栏从片段A切换到片段B并没有问题，但当我尝试从浮动操作按钮切换到片段c时，它给了我错误

java.lang.IllegalStateException:View androidx.constraintlayout.widget.constraintlayout{65bf79f V.E……...0,0-10801529#7f0800b2 app:id/frameLayout}没有导航控制器集

class MainActivity : AppCompatActivity() {

    private lateinit var navController: NavController

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

        val dateView = findViewById<TextView>(R.id.dateTextView)
        dateView.text = getMonth()

        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_frag) as NavHostFragment
        navController = navHostFragment.navController

        setupActionBarWithNavController(navController)

        val chartFrag = ChartsFragment()
        val infoData = info_data()

        val botNav = findViewById<BottomNavigationView>(R.id.botNavigation)
        botNav.setOnNavigationItemSelectedListener {
            when(it.itemId){
                R.id.menu_statement ->{
                    setCurrentFragment(infoData)
                }
                R.id.menu_charts ->{
                    setCurrentFragment(chartFrag)
                }
            }
            true
        }

    }


    fun setCurrentFragment(fragment: Fragment) = supportFragmentManager.beginTransaction().apply{
        replace(R.id.nav_host_frag, fragment)
        commit()
    }

    fun getMonth():String{
        val calendar = Calendar.getInstance()
        val simpleDateFormat = SimpleDateFormat("MMM yyyy")
        val date = simpleDateFormat.format(calendar.time)
        return date
    }
    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

class info_data : Fragment() {
    val dataSet = dataSource().loadData()
    val adapter = RecyclerViewAdapter(dataSet)

    companion object{
        var income = 0.0
        var expense = 0.0
    }

    lateinit var navController: NavController

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_info_data, container, false)
    }

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

        val tvExpense = view.findViewById<TextView>(R.id.tvExpense)
        tvExpense.text = "Expense : \n$ "+expense.toString()

        val tvIncome = view.findViewById<TextView>(R.id.tvIncome)
        tvIncome.text = "Income : \n$ "+income.toString()

        val tvTotal = view.findViewById<TextView>(R.id.tvTotal)
        tvTotal.text = "Total : \n$ "+grandTotal().toString()

        val rv= view.findViewById<RecyclerView>(R.id.recyclerView)
        rv.adapter = adapter
        rv.layoutManager = LinearLayoutManager(activity)

        val floatingBtn = view.findViewById<FloatingActionButton>(R.id.fabBtn)
        floatingBtn.setOnClickListener(){
            goToNextScreen(view)
        }
    }

    fun goToNextScreen(view: View){
        navController = Navigation.findNavController(view)
        navController!!.navigate(R.id.action_info_data_to_form_data2)
    }

    fun grandTotal():Double{
        val inc = income
        val exp = expense
        val total = inc-exp
        return total
    }
}

代码如下：

MainActivity.kt

class MainActivity : AppCompatActivity() {

    private lateinit var navController: NavController

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

        val dateView = findViewById<TextView>(R.id.dateTextView)
        dateView.text = getMonth()

        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_frag) as NavHostFragment
        navController = navHostFragment.navController

        setupActionBarWithNavController(navController)

        val chartFrag = ChartsFragment()
        val infoData = info_data()

        val botNav = findViewById<BottomNavigationView>(R.id.botNavigation)
        botNav.setOnNavigationItemSelectedListener {
            when(it.itemId){
                R.id.menu_statement ->{
                    setCurrentFragment(infoData)
                }
                R.id.menu_charts ->{
                    setCurrentFragment(chartFrag)
                }
            }
            true
        }

    }


    fun setCurrentFragment(fragment: Fragment) = supportFragmentManager.beginTransaction().apply{
        replace(R.id.nav_host_frag, fragment)
        commit()
    }

    fun getMonth():String{
        val calendar = Calendar.getInstance()
        val simpleDateFormat = SimpleDateFormat("MMM yyyy")
        val date = simpleDateFormat.format(calendar.time)
        return date
    }
    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

class info_data : Fragment() {
    val dataSet = dataSource().loadData()
    val adapter = RecyclerViewAdapter(dataSet)

    companion object{
        var income = 0.0
        var expense = 0.0
    }

    lateinit var navController: NavController

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_info_data, container, false)
    }

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

        val tvExpense = view.findViewById<TextView>(R.id.tvExpense)
        tvExpense.text = "Expense : \n$ "+expense.toString()

        val tvIncome = view.findViewById<TextView>(R.id.tvIncome)
        tvIncome.text = "Income : \n$ "+income.toString()

        val tvTotal = view.findViewById<TextView>(R.id.tvTotal)
        tvTotal.text = "Total : \n$ "+grandTotal().toString()

        val rv= view.findViewById<RecyclerView>(R.id.recyclerView)
        rv.adapter = adapter
        rv.layoutManager = LinearLayoutManager(activity)

        val floatingBtn = view.findViewById<FloatingActionButton>(R.id.fabBtn)
        floatingBtn.setOnClickListener(){
            goToNextScreen(view)
        }
    }

    fun goToNextScreen(view: View){
        navController = Navigation.findNavController(view)
        navController!!.navigate(R.id.action_info_data_to_form_data2)
    }

    fun grandTotal():Double{
        val inc = income
        val exp = expense
        val total = inc-exp
        return total
    }
}

class MainActivity:AppCompatActivity（）{
专用lateinit var navController:navController
重写创建时的乐趣（savedInstanceState:Bundle？）{
super.onCreate（savedInstanceState）
setContentView（R.layout.activity_main）
val dateView=findviewbyd（R.id.dateTextView）
dateView.text=getMonth（）
val navHostFragment=supportFragmentManager.findFragmentById（R.id.nav_host_frag）作为navHostFragment
navController=navHostFragment.navController
setupActionBarWithNavController（navController）
val chartFrag=ChartsFragment（）
val infoData=info_data（）
val botNav=findviewbyd（R.id.botNavigation）
botNav.setOnNavigationItemSelectedListener{
何时（it.itemId）{
R.id.菜单\声明->{
setCurrentFragment（信息数据）
}
R.id.菜单\图表->{
setCurrentFragment（chartFrag）
}
}
真的
}
}
fun setCurrentFragment（fragment:fragment）=supportFragmentManager.beginTransaction（）.apply{
替换（R.id.nav_主机_碎片，碎片）
提交（）
}
fun getMonth（）：字符串{
val calendar=calendar.getInstance（）
val simpleDateFormat=simpleDateFormat（“MMM-yyy”）
val date=simpleDateFormat.format（calendar.time）
返回日期
}
覆盖支持NavigateUp（）：布尔值{
返回navController.navigateUp（）| | super.onSupportNavigateUp（）
}
}

信息数据.kt

class MainActivity : AppCompatActivity() {

    private lateinit var navController: NavController

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

        val dateView = findViewById<TextView>(R.id.dateTextView)
        dateView.text = getMonth()

        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_frag) as NavHostFragment
        navController = navHostFragment.navController

        setupActionBarWithNavController(navController)

        val chartFrag = ChartsFragment()
        val infoData = info_data()

        val botNav = findViewById<BottomNavigationView>(R.id.botNavigation)
        botNav.setOnNavigationItemSelectedListener {
            when(it.itemId){
                R.id.menu_statement ->{
                    setCurrentFragment(infoData)
                }
                R.id.menu_charts ->{
                    setCurrentFragment(chartFrag)
                }
            }
            true
        }

    }


    fun setCurrentFragment(fragment: Fragment) = supportFragmentManager.beginTransaction().apply{
        replace(R.id.nav_host_frag, fragment)
        commit()
    }

    fun getMonth():String{
        val calendar = Calendar.getInstance()
        val simpleDateFormat = SimpleDateFormat("MMM yyyy")
        val date = simpleDateFormat.format(calendar.time)
        return date
    }
    override fun onSupportNavigateUp(): Boolean {
        return navController.navigateUp() || super.onSupportNavigateUp()
    }
}

class info_data : Fragment() {
    val dataSet = dataSource().loadData()
    val adapter = RecyclerViewAdapter(dataSet)

    companion object{
        var income = 0.0
        var expense = 0.0
    }

    lateinit var navController: NavController

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_info_data, container, false)
    }

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

        val tvExpense = view.findViewById<TextView>(R.id.tvExpense)
        tvExpense.text = "Expense : \n$ "+expense.toString()

        val tvIncome = view.findViewById<TextView>(R.id.tvIncome)
        tvIncome.text = "Income : \n$ "+income.toString()

        val tvTotal = view.findViewById<TextView>(R.id.tvTotal)
        tvTotal.text = "Total : \n$ "+grandTotal().toString()

        val rv= view.findViewById<RecyclerView>(R.id.recyclerView)
        rv.adapter = adapter
        rv.layoutManager = LinearLayoutManager(activity)

        val floatingBtn = view.findViewById<FloatingActionButton>(R.id.fabBtn)
        floatingBtn.setOnClickListener(){
            goToNextScreen(view)
        }
    }

    fun goToNextScreen(view: View){
        navController = Navigation.findNavController(view)
        navController!!.navigate(R.id.action_info_data_to_form_data2)
    }

    fun grandTotal():Double{
        val inc = income
        val exp = expense
        val total = inc-exp
        return total
    }
}

class-info\u数据：Fragment（）{
val dataSet=dataSource（）.loadData（）
val适配器=RecycleServiceAdapter（数据集）
伴星{
风险值收益=0.0
风险值费用=0.0
}
lateinit var navController:navController
覆盖创建视图(
充气器：布局充气器，容器：视图组？，
savedInstanceState:捆绑？
)：查看{
//为该碎片膨胀布局
返回充气器。充气（R.layout.fragment\u info\u数据，容器，错误）
}
覆盖已创建的视图（视图：视图，保存状态：捆绑？）{
super.onViewCreated（视图，savedInstanceState）
val tvExpense=view.findViewById（R.id.tvExpense）
tvExpense.text=“费用：\n$”+费用.toString（）
val tvIncome=view.findViewById（R.id.tvIncome）
tvIncome.text=“收入：\n$”+收入.toString（）
val tvTotal=view.findViewById（R.id.tvTotal）
tvTotal.text=“总计：\n$”+grandTotal（）.toString（）
val rv=view.findViewById（R.id.recyclerView）
rv.适配器=适配器
rv.layoutManager=LinearLayoutManager（活动）
val floatingBtn=view.findViewById（R.id.fabBtn）
floatingBtn.setOnClickListener（）{
goToNextScreen（视图）
}
}
趣味goToNextScreen（视图：视图）{
navController=Navigation.findNavController（视图）
导航控制器！！.导航（R.id.action\u info\u data\u至\u form\u data2）
}
fun grandTotal（）：双倍{
val公司=收入
val exp=费用
val总计=inc exp
返回总数
}
}

**错误： 位于androidx.navigation.navigation.findNavController（navigation.java:84）

在com.example.myapplication.info_data.goToNextScreen上（info_data.kt:58）

---

在com.example.myapplication.info_data.onViewCreated$lambda-0（info_data.kt:53）**

中，您使用的是

NavHostFragment

，这意味着您根本不应该执行

碎片事务。有什么原因你不遵守规则吗？非常感谢。非常感谢。