Navigation Drawer Back Stack不起作用

Question

我有一个开发如下图所示的应用程序：

因此是带有菜单的片段A。单击菜单将打开片段B。我的问题是，当我单击“后退”按钮时，什么也没发生，所以我无法从片段B返回片段A，而且我也不明白为什么。

这是我的代码：

主要活动

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        final DrawerLayout drawer = findViewById(R.id.drawer_layout);
        final ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, 
                R.string.navigation_drawer_close);

        drawer.setDrawerListener(toggle);
        toggle.syncState();

        drawer.openDrawer(Gravity.LEFT);

        NavigationView navigationView = findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        FragmentA fragmentA = new FragmentA();
        FragmentManager manager = getSupportFragmentManager();
        manager.beginTransaction().replace(R.id.relativelayout_for_fragment, fragmentA, fragmentA.getTag()).commit();
        getSupportActionBar().setTitle(getResources().getString(R.string.title));

        getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                if(getSupportFragmentManager().getBackStackEntryCount() == 0){
                    drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED);
                    toggle.setDrawerIndicatorEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    getSupportActionBar().setHomeButtonEnabled(false);
                }else{
                    drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
                    toggle.setDrawerIndicatorEnabled(false);
                    getSupportActionBar().setHomeButtonEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
                }
            }
        });
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = findViewById(R.id.drawer_layout);
        int count = getSupportFragmentManager().getBackStackEntryCount();

        if (count == 0) {
            drawer.openDrawer(GravityCompat.START);
        } else {
            getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
        }
    }

片段A（在菜单上单击）

Fragment fragmentB = new FragmentB();
FragmentTransaction transaction = activity.getFragmentManager().beginTransaction();
transaction.replace(R.id.relativelayout_for_fragment, fragmentB);
transaction.addToBackStack(null);
transaction.commit();

片段B

@Override
public void onCreateOptionsMenu(@NonNull Menu menu, MenuInflater inflater) {
    inflater.inflate(R.menu.share_menu, menu);
    super.onCreateOptionsMenu(menu, inflater);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    switch (item.getItemId()) {
        case android.R.id.home:
            getFragmentManager().popBackStack();
            return true;
        case R.id.menu_item_share:
            String contenuto = "*" + titolo + "*" + "\n" + desc;
            String textToShare = getResources().getString(R.string.Linc);
            Intent intent = new Intent("android.intent.action.SEND");
            intent.setType("text/plain");
            intent.putExtra("android.intent.extra.TEXT", contenuto + "\n\n" + textToShare);
            startActivity(Intent.createChooser(intent, 
                getResources().getString(R.string.sharing)));
            return true;
    }
    return super.onOptionsItemSelected(item);
}

Answer 1

您是否尝试过此onBackPressed

override fun onBackPressed() {
            val manager: FragmentManager = supportFragmentManager
            if(manager.backStackEntryCount > 0){
                manager.popBackStack()
            }else{
                super.onBackPressed()
            }
        }

Answer 2

替换

getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                if(getSupportFragmentManager().getBackStackEntryCount() == 0){
                    drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED);
                    toggle.setDrawerIndicatorEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    getSupportActionBar().setHomeButtonEnabled(false);
                }else{
                    drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
                    toggle.setDrawerIndicatorEnabled(false);
                    getSupportActionBar().setHomeButtonEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
                }
            }
        });
    }

有

getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
            @Override
            public void onBackStackChanged() {
                if(getSupportFragmentManager().getBackStackEntryCount() == 0){
                    drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_UNLOCKED);
                    toggle.setDrawerIndicatorEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                    getSupportActionBar().setHomeButtonEnabled(false);
                }else{
                    drawer.setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
                    toggle.setDrawerIndicatorEnabled(false);
                    getSupportActionBar().setHomeButtonEnabled(true);
                    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
            getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
 getSupportFragmentManager().beginTransaction().replace(R.id.relativelayout_for_fragment, new FragmentA(), "FRAGMENT_A").commit();



                }
            }
        });
    }