底部导航栏只显示HomeFragment，不显示其他fragment

Question

我有一个底部导航栏可以在片段之间切换，我在 MainActivity 中的功能正在工作，但是当我单击底部导航按钮时，屏幕停留在 HomeFragment 上，不会更改为NotificationsFragment。

我在MainActivity中的函数

private fun replaceFragment(fragment: Fragment){
        val fragmentManager = supportFragmentManager
        val fragmentTransaction = fragmentManager.beginTransaction()
        fragmentTransaction.replace(R.id.frameLayout,fragment)
        fragmentTransaction.commit()
        Log.e("navR","hereeee!!!!333")
    }

我在 onCreate() 中的代码

replaceFragment(HomeFragment())
        binding.bottomNavigationView.setOnItemSelectedListener {
            when(it.itemId){
                R.id.home_page-> {replaceFragment(HomeFragment())
                    Log.e("nav","Home")
                }
                R.id.notifications_page-> {replaceFragment(NotificationsFragment())
                    Log.e("nav","Notifications")
                }
                else->{ }
            }
            true
        }

这是 MainActivity 的 xml 文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:openDrawer="start">

    <!-- Main content -->
    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            android:layout_alignParentEnd="true"
            android:layout_marginStart="0dp"
            android:layout_marginTop="0dp"
            android:layout_marginEnd="0dp"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottomNavigationView"
            android:layout_width="match_parent"
            android:layout_height="67dp"
            android:layout_alignParentStart="true"
            android:layout_alignParentEnd="true"
            android:layout_alignParentBottom="true"
            android:layout_marginStart="0dp"
            android:layout_marginEnd="0dp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:menu="@menu/bottom_nav" />

        <FrameLayout
            android:id="@+id/frameLayout"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_above="@+id/bottomNavigationView"
            android:layout_below="@+id/toolbar"
            android:layout_alignParentStart="true"
            android:layout_alignParentEnd="true"
            app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/toolbar">

        </FrameLayout>

    </RelativeLayout>

    <!-- Navigation view -->
    <com.google.android.material.navigation.NavigationView
        android:id="@+id/navigation_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/side_nav"
        app:menu="@menu/nav" />

</androidx.drawerlayout.widget.DrawerLayout>

首页片段 这里必须显示NotificationsFragment但不起作用

Answer 1

尝试下面的代码

package com.example.myapplication

import android.os.Bundle
import com.google.android.material.bottomnavigation.BottomNavigationView
import androidx.appcompat.app.AppCompatActivity
import androidx.navigation.findNavController
import androidx.navigation.ui.AppBarConfiguration
import androidx.navigation.ui.setupActionBarWithNavController
import androidx.navigation.ui.setupWithNavController
import com.example.myapplication.databinding.ActivityMainBinding
import com.example.myapplication.ui.home.HomeFragment
import com.example.myapplication.ui.notifications.NotificationsFragment

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
        val navView: BottomNavigationView = binding.navView
        addFragment()
        navView.setOnItemSelectedListener {
            when(it.itemId) {
                R.id.navigation_home -> {
                    val fragmentManager = supportFragmentManager
                    val fragmentTransaction = fragmentManager.beginTransaction()
                    fragmentTransaction.replace(R.id.fragment_container,HomeFragment())
                    fragmentTransaction.commit()
                }
                R.id.navigation_notifications -> {
                    val fragmentManager = supportFragmentManager
                    val fragmentTransaction = fragmentManager.beginTransaction()
                    fragmentTransaction.replace(R.id.fragment_container,NotificationsFragment())
                    fragmentTransaction.commit()
                }
                else -> {

                }
            }
            true
        }
    }

    fun addFragment() {
        val fragmentManager = supportFragmentManager
        val fragmentTransaction = fragmentManager.beginTransaction()
        fragmentTransaction.add(R.id.fragment_container,HomeFragment())
        fragmentTransaction.commit()
    }
}

活动 XML

    <?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

    <FrameLayout
        android:id="@+id/fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>