在 Android Kotlin 中实现底部导航栏时出错

如何解决在 Android Kotlin 中实现底部导航栏时出错

我是安卓开发的新手。 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 中有一个指向片段 c 的浮动操作按钮。 我通过导航栏从片段 A 切换到 B 没有问题，但是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：查看 androidx.constraintlayout.widget.ConstraintLayout{65bf79f VE ..... 0,0-1080,1529 #7f0800b2 app:id/frameLayout } 没有设置 NavController

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()
    }
}

info_data.kt

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
    }
}

**错误： 在 androidx.navigation.Navigation.findNavController(Navigation.java:84)

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

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