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The behavior of the BottomNavigationView back button should work as a Youtube application, but it crashes

Steps to play:

  • Launch a new Android project, select " BottomNavigationView": enter image description here

  • Replace MainActivity with the following:

    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)
}
}

  • Create 3 new classes, FragmentA, FragmentB and 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)
}
}

with this 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>
  • Run the application
  • Press "Dashboard" - fragment B is displayed
  • Click "Notifications" - fragment C is displayed
  • Press "Dashboard" - fragment B is displayed
  • Press "Home" - fragment A is displayed
  • Press the back button - fragment B is displayed
  • Press the "Back" button - fragment C will appear - "Application Failure"
  • Press the "Back" button - fragment A will appear - the application is broken.
  • Click the "Back" button - the application will shut down. - The application is broken.

,

StackTrace:

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)
+6
3

" ( ) backstack", backstack (deque):

class MainActivity extends AppCompatActivity {
    private BottomNavigationView navigation;
    // initialize with number of different fragments
    private Deque<Integer> fragmentIds = new ArrayDeque<>(3);

    private FragmentA fragmentA = new FragmentA();
    private FragmentB fragmentB = new FragmentB();
    private FragmentC fragmentC = new FragmentC();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fragmentIds.push(R.id.navigation_home);
        showTabWithoutAddingToBackStack(fragmentA);
        navigation = findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(onNavigationItemClicked);
    }

    private BottomNavigationView.OnNavigationItemSelectedListener onNavigationItemClicked = new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            item.setChecked(true);
            int itemId = item.getItemId();
            if (fragmentIds.contains(itemId)) {
                fragmentIds.remove(itemId);
            }
            fragmentIds.push(itemId);
            showTabWithoutAddingToBackStack(getFragment(item.getItemId()));
            return true;
        }
    };

    private Fragment getFragment(int fragmentId) {
        switch (fragmentId) {
            case R.id.navigation_home:
                return fragmentA;
            case R.id.navigation_dashboard:
                return fragmentB;
            case R.id.navigation_notifications:
                return fragmentC;
        }
        return fragmentA;
    }

    void showTabWithoutAddingToBackStack(Fragment fragment) {
        getSupportFragmentManager().beginTransaction().replace(R.id.container, fragment, fragment.getClass().getSimpleName()).commit();
    }

    void setBottomTab(int id) {
        int itemIndex;
        switch (id) {
            case R.id.navigation_dashboard:
                itemIndex = 1;
                break;
            case R.id.navigation_notifications:
                itemIndex = 2;
                break;
            default:
            case R.id.navigation_home:
                itemIndex = 0;
        }
        navigation.getMenu().getItem(itemIndex).setChecked(true);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
            onBackPressed();
            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public void onBackPressed() {
        fragmentIds.pop();
        if (!fragmentIds.isEmpty()) {
            showTabWithoutAddingToBackStack(getFragment(fragmentIds.peek()));
        } else {
            finish();
        }
    }
}
0

, 100 . , ,

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 fun updateView(fragmentId: Int) {
    var exists = false
    fragmentIds
            .filter { it == fragmentId }
            .forEach { exists = true }

    if (exists) {
        showTab(getFragment(fragmentId))
        setBottomTab(fragmentId)
    } else {
        fragmentIds.add(fragmentId)
        showTab(getFragment(fragmentId))
    }
}

!!!

0

, Bottombar. GitHub. , , .

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

Output example

enter image description here

0
source

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