我想在我的项目中制作一个底部导航栏。每个 View 都有自己的 fragment 。问题是，每次我点击按钮更改 View ，例如从最近到 Collection 夹，它都会创建具有全新状态的新 fragment (例如，滚动位置，无论我的 fragment 包含什么，文本都会改变)。我知道在官方 Android 文档中写着底部导航栏应该重置任务状态，但我认为这对用户来说太不舒服了。 我想拥有类似 instagram 的功能，您可以从提要更改为探索，然后返回到提要滚动位置图像缓存所有内容都保留下来。我几乎尝试了所有方法来解决这个问题，唯一有效的方法是根据情况设置可见性 GONE 和设置可见性 VISIBLE，但我知道这不是正确的方法，应该有更好的方法，我不是在谈论手动保存需要的实例。我几乎遵循了所有关于底部导航 fragment 的教程，但有趣的是，没有人有兴趣在每次不调用 new 的情况下使用它。

FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
fragmentTransaction.replace(R.id.frameLayout, FirstFragment.newInstance());
fragmentTransaction.commit();

bottomNavigationView = (BottomNavigationView) findViewById(R.id.navigation);
bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Fragment fragment = null;
        switch (item.getItemId()) {
            case R.id.menu_dialer:
                fragment = FirstFragment.newInstance();
                break;
            case R.id.menu_email:
                fragment = SecondFragment.newInstance();
                break;
            case R.id.menu_map:
                fragment = ThirdFragment.newInstance();
                break;
        }
        if (fragment != null) {
            FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.frameLayout, fragment);
            fragmentTransaction.commit();
        }
        return true;
    }
});

我也尝试了 onAttach 和 Deattach 解决方案，但还是没有成功。

VIDEO LINK : new i tried Nino Handler version it only works when i tap on the same fragment button

可能与我使用的金丝雀版本有关，或者我的 gradle 依赖项有问题？

新更新:

public class MainActivity extends AppCompatActivity {

    private TextView mTextMessage;


    private static final String TAG_FRAGMENT_ONE = "fragment_one";
    private static final String TAG_FRAGMENT_TWO = "fragment_two";

    private FragmentManager fragmentManager;
    private Fragment currentFragment;

    String TAG = "babken";
    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        Fragment fragment = null;
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                   fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_ONE);
                    if (fragment == null) {
                        fragment = FragmentFirst.newInstance();
                    }
                    replaceFragment(fragment, TAG_FRAGMENT_ONE);

                    break;
                case R.id.navigation_dashboard:

                     fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_TWO);
                    if (fragment == null) {
                        fragment = FragmentSecond.newInstance();
                    }
                    replaceFragment(fragment, TAG_FRAGMENT_TWO);

                    break;
            }
            return true;

        }
    };

    private void replaceFragment(@NonNull Fragment fragment, @NonNull String tag) {
        if (!fragment.equals(currentFragment)) {
            fragmentManager
                    .beginTransaction()
                    .replace(R.id.armen, fragment, tag)
                    .commit();
            currentFragment = fragment;
        }
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fragmentManager = getSupportFragmentManager();
        Fragment fragment = fragmentManager.findFragmentByTag(TAG_FRAGMENT_ONE);
        if (fragment == null) {
            fragment = FragmentFirst.newInstance();
        }
        replaceFragment(fragment, TAG_FRAGMENT_ONE);
        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
    }

}

最佳答案

我有类似的问题，但这段代码解决了我的问题。

public class MainActivity extends AppCompatActivity {

    boolean doubleBackToExitPressedOnce = false;
    final Fragment fragment1 = new HomeFragment();
    final Fragment fragment2 = new DashboardFragment();
    final Fragment fragment3 = new NotificationsFragment();
    final FragmentManager fm = getSupportFragmentManager();
    Fragment active = fragment1;
    BottomNavigationView navigation;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
        setFragment(fragment1, "1", 0);
    }


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

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    setFragment(fragment1, "1", 0);
                    return true;
                case R.id.navigation_dashboard:
                    setFragment(fragment2, "2", 1);
                    return true;
                case R.id.navigation_notifications:
                    setFragment(fragment3, "3", 2);
                    return true;
            }
            return false;
        }
    };

    public void setFragment(Fragment fragment, String tag, int position) {
        if (fragment.isAdded()) {
            fm.beginTransaction().hide(active).show(fragment).commit();
        } else {
            fm.beginTransaction().add(R.id.main_container, fragment, tag).commit();
        }
        navigation.getMenu().getItem(position).setChecked(true);
        active = fragment;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            startActivity(new Intent(MainActivity.this, SettingsActivity.class));
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onBackPressed() {
        if (active == fragment1) {
            if (doubleBackToExitPressedOnce) {
                super.onBackPressed();
                return;
            }
            this.doubleBackToExitPressedOnce = true;
            Toast.makeText(this, "Please click BACK again to exit", Toast.LENGTH_SHORT).show();
        } else {
            setFragment(fragment1, "1", 0);
        }
    }
}

关于java - BottomNavigationView - 如何避免重新创建 fragment 并重用它们，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45130713/