Question

重现的步骤：

启动新的Android项目，选择“BottomNavigationView”：

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)
}
}

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)
}
}

使用此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>

启动应用
按“仪表板” - 显示片段B
按“通知” - 显示片段C
按“仪表板” - 显示片段B
按“主页” - 显示片段A
按返回按钮 - 显示片段B
按返回按钮 - 应显示片段C - 应用程序崩溃
按返回按钮 - 应显示片段A - 应用程序崩溃
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)

Answer 1

我使用Bottombar库实现了这个概念。我已经上传到GitHub了。如有任何问题，请在这里查看并发表评论。

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

示例输出

Answer 2

这使您可以使用自定义后台堆栈（deque）进行“不要在backstack上重复（但重新排序）我的片段”行为：

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();
        }
    }
}

Answer 3

我必须稍微更改它并让它工作，我已经测试了多个设备并在一次测试运行中切换标签超过100次。它工作正常，更改代码，

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))
    }
}

到这个新代码，

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))
    }
}

就是这样!!!

Answer 4

您好，请检查是否已完成并正常工作。您可以检查一下。 https://github.com/sandeshsk/BackStackFragmentRedirectsToHome

如果有任何问题，请更新。

这是分配片段的方法

public void addFragment(FragmentManager fragmentManager,
                               Fragment fragment,
                               int containerId,boolean isFromHome){

    fragmentManager.popBackStack(null,FragmentManager.POP_BACK_STACK_INCLUSIVE);

    FragmentTransaction fragmentTransaction=fragmentManager.beginTransaction();
    if(isFromHome){
        fragmentTransaction.replace(containerId,fragment);
    }else{
        fragmentTransaction.add(new HomeFragment(),"Home");
        fragmentTransaction.addToBackStack("Home");
    }
    fragmentTransaction.replace(containerId,fragment).commit();

}

这是您的导航项目侦听器

 private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
              if (getSupportFragmentManager().getBackStackEntryCount() == 0) {
                    addFragment(getSupportFragmentManager(), new HomeFragment(), R.id.frame, true);
                }else{
                    getSupportFragmentManager().popBackStack();
                }
                return true;
            case R.id.navigation_dashboard:
                addFragment(getSupportFragmentManager(),new DashboardFragment(),R.id.frame,false);
                return true;
            case R.id.navigation_notifications:
                addFragment(getSupportFragmentManager(),new NotificationFragment(),R.id.frame,false);
                return true;
            case R.id.navigation_setting:
                addFragment(getSupportFragmentManager(),new SettingFragment(),R.id.frame,false);
                return true;
        }
        return false;
    }
};

onBackPressed方法

 @Override
public void onBackPressed() {
    if(getSupportFragmentManager().getBackStackEntryCount()>0){
        navigation.setSelectedItemId(R.id.navigation_home);
    }else {
        super.onBackPressed();
    }
}

Answer 5

如果您想返回堆栈中的所有项目（不仅是首页），例如Youtube，请尝试以下代码：

BottomNavigationView bottomNavigationView;
FragmentTransaction transaction;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);

    bottomNavigationView.setOnNavigationItemSelectedListener
            (new BottomNavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                    Fragment selectedFragment = null;
                    switch (item.getItemId()) {
                        case R.id.action_item1:
                            selectedFragment = ItemOneFragment.newInstance();
                            break;
                        case R.id.action_item2:
                            selectedFragment = ItemTwoFragment.newInstance();
                            break;
                        case R.id.action_item3:
                            selectedFragment = ItemThreeFragment.newInstance();
                            break;
                        case R.id.action_item4:
                            selectedFragment = ItemFourFragment.newInstance();
                            break;
                        case R.id.action_item5:
                            selectedFragment = ItemFiveFragment.newInstance();
                            break;
                    }
                    transaction = getSupportFragmentManager().beginTransaction();
                    transaction.replace(R.id.frame_layout, selectedFragment);
                    transaction.addToBackStack(null);
                    transaction.commit();
                    return true;
                }
            });

    //Manually displaying the first fragment - one time only
    transaction = getSupportFragmentManager().beginTransaction();
    transaction.replace(R.id.frame_layout, ItemOneFragment.newInstance());
    transaction.commit();

}

@Override
public void onBackPressed() {
    int count = getSupportFragmentManager().getBackStackEntryCount();
    if (count == 0) {
        super.onBackPressed();
    } else {
        int index = ((getSupportFragmentManager().getBackStackEntryCount()) -1);
        getSupportFragmentManager().popBackStack();
        FragmentManager.BackStackEntry backEntry = getSupportFragmentManager().getBackStackEntryAt(index);
        int stackId = backEntry.getId();
        bottomNavigationView.getMenu().getItem(stackId).setChecked(true);
    }
}

BottomNavigationView后退按钮行为应该像Youtube App一样工作但崩溃

5 个答案: