重现步骤:

1. 开始一个新的 Android 项目，选择“BottomNavigationView”:

2. 将 MainActivity 替换为:

   class MainActivity : AppCompatActivity() {
   
   private var fragmentIds = ArrayList<Int>()
   
   val fragmentA: FragmentA = FragmentA()
   private val fragmentB = FragmentB()
   private val fragmentC = FragmentC()
   
   private fun getFragment(fragmentId: Int): Fragment {
       when (fragmentId) {
           R.id.navigation_home -> {
               return fragmentA
           }
           R.id.navigation_dashboard -> {
               return fragmentB
           }
           R.id.navigation_notifications -> {
               return fragmentC
           }
       }
       return fragmentA
   }
   
   private fun updateView(fragmentId: Int) {
       var exists = false
       fragmentIds
               .filter { it == fragmentId }
               .forEach { exists = true }
   
       if (exists) {
           fragmentIds.remove(fragmentId)
           showTabWithoutAddingToBackStack(getFragment(fragmentId))
       } else {
           fragmentIds.add(fragmentId)
           showTab(getFragment(fragmentId))
       }
   }
   
   private val onNavigationItemClicked = BottomNavigationView.OnNavigationItemSelectedListener { item ->
       when (item.itemId) {
           R.id.navigation_home -> {
               updateView(R.id.navigation_home)
               return@OnNavigationItemSelectedListener true
           }
           R.id.navigation_dashboard -> {
               updateView(R.id.navigation_dashboard)
               return@OnNavigationItemSelectedListener true
           }
           R.id.navigation_notifications -> {
               updateView(R.id.navigation_notifications)
               return@OnNavigationItemSelectedListener true
           }
       }
       false
   }
   
   override fun onCreate(savedInstanceState: Bundle?) {
       super.onCreate(savedInstanceState)
       setContentView(R.layout.activity_main)
       showTabWithoutAddingToBackStack(fragmentA)
   
       navigation.setOnNavigationItemSelectedListener(onNavigationItemClicked)
   
   }
   
   private fun showTab(fragment: Fragment) {
       supportFragmentManager
               .beginTransaction()
               .replace(R.id.main_container, fragment, fragment::class.java.simpleName)
               .addToBackStack(fragment::class.java.simpleName)
               .commit()
   }
   
   fun showTabWithoutAddingToBackStack(fragment: Fragment) {
       supportFragmentManager
               .beginTransaction()
               .replace(R.id.main_container, fragment, fragment::class.java.simpleName)
               .commit()
   }
   
   fun setBottomTab(id: Int) {
       navigation.setOnNavigationItemSelectedListener(null)
       navigation.selectedItemId = id
       // currentTab = id
       navigation.setOnNavigationItemSelectedListener(onNavigationItemClicked)
   }
   }
   

3. 创建 3 个新类，FragmentA、FragmentB 和 FragmentC:

   class FragmentA : Fragment() {
   
   override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
       setHasOptionsMenu(true)
       return inflater.inflate(R.layout.fragment_a, container, false)
   }
   
   override fun onResume() {
       super.onResume()
       val act = activity as MainActivity
       act.setBottomTab(R.id.navigation_home)
   }
   }
   

使用这个 xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Fragment A" />
</LinearLayout>

1. 启动应用
2. 按“仪表板”- 显示 fragment B
3. 按“通知”- 显示 fragment C
4. 按“仪表板”- 显示 fragment B
5. 按“主页”- 显示 fragment A
6. 按“后退”按钮 - 显示 fragment B
7. 按返回按钮 - 应显示 fragment C - 应用程序崩溃
8. 按“后退”按钮 - 应显示 fragment A - 应用程序崩溃
9. 按返回按钮 - 应用程序关闭。 - 应用程序崩溃

Here is a video that demonstrates above steps

堆栈跟踪:

12-06 12:58:35.899 25903-25903/com.example.jimclermonts.bottomnavigationview E/InputEventSender: Exception dispatching finished signal.
12-06 12:58:35.900 25903-25903/com.example.jimclermonts.bottomnavigationview E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
12-06 12:58:35.912 25903-25903/com.example.jimclermonts.bottomnavigationview E/MessageQueue-JNI: java.lang.**IllegalStateException: Fragment already added**: FragmentB{3aac1d9 #1 id=0x7f080059 FragmentB}
                                                                                                     at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1882)
                                                                                                     at android.support.v4.app.BackStackRecord.executePopOps(BackStackRecord.java:825)
                                                                                                     at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2577)
                                                                                                     at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2367)
                                                                                                     at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2322)
                                                                                                     at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:851)
                                                                                                     at android.support.v4.app.FragmentManagerImpl.popBackStackImmediate(FragmentManager.java:794)
                                                                                                     at android.support.v4.app.FragmentActivity.onBackPressed(FragmentActivity.java:174)

最佳答案

我已经使用 Bottombar 库实现了这个概念。我已经上传到GitHub。如果有任何问题，请在此处检查和评论。

https://github.com/itvignes09/youtube-like-bttom-menu

示例输出

关于android - BottomNavigationView 后退按钮行为应该像 Youtube 应用程序一样工作但崩溃，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47435967/