Question

我需要实现我的应用程序的UI，就像Instagram那样。我需要使用底部导航视图从不同的片段切换，但我需要保持片段的状态，就像我离开它们一样。我怎样才能做到这一点？

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    item.setChecked(true);
    switch (item.getItemId()) {
        case R.id.action_formation:
            if (homeFragment == null) {
                homeFragment = new HomeFragment();
            }
            displayFragment(homeFragment);
            break;
        case R.id.action_result:
            if (introResultFragment == null) {
                introResultFragment = new IntroResultFragment();
            }
            displayFragment(introResultFragment);
            break;

        case R.id.action_market:
            displayFragment(new MarketFragment());
            break;
    }
    return false;
}


public void displayFragment(final Fragment fragment) {
    FragmentManager fragmentManager = getFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager
            .beginTransaction();
    fragmentTransaction.replace(R.id.container, fragment, fragment.getClass().toString());
    fragmentTransaction.commit();
}

Answer 1

已经有很长时间了，但是我想在github中提供我的开源库，该库实现了Youtube和Instagram的相同UX： https://github.com/ZachBublil/ZNavigator

您必须将此依赖项添加到gradle：

compile 'com.zach.znavigator:znavigator:1.0.0'

您唯一要做的就是在BottomNavigationView中传递您想要的片段列表：

  public class SampleActivity extends NavigationActivity {

    private BottomNavigationView navigationView;

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

        LinkedHashMap<Integer, Fragment> rootFragments = new LinkedHashMap<>();
        rootFragments.put(R.id.tab1, new FirstTab());
        rootFragments.put(R.id.tab2,new SecondTab());
        rootFragments.put(R.id.tab3, new ThirdTab());
        init(rootFragments, R.id.container);

        navigationView.setOnNavigationItemSelectedListener(this);
        navigationView.setOnNavigationItemReselectedListener(this);
    }

    @Override
    public void tabChanged(int id) {
        navigationView.getMenu().findItem(id).setChecked(true);
    }
}

如果要在其中一个选项卡中打开新片段作为内部屏幕，则可以通过使用选项卡片段中的ZNavigation类来做到这一点：

ZNavigation.openChildFragment(getFragmentManager(),new ChildFragment());

Answer 2

只需记住活动片段，并使用userVisiableHint在每个片段中获取活动状态。

private Fragment currentFragment; // need to be init

private void switch2Fragment(Fragment target){
    getFragmentManager().executePendingTransactions();
    if(target.isAdded){
        getFragmentManager().beginTransaction().hide(currentFragment).show(target).commit();
    } else {
        getFragmentManager().beginTransaction().hide(currentFragment).add(R.id.xxx, target).commit();
    }
    currentFragment.setUserVisibleHint(false);
    currentFragment = target;
    target.setUserVisibleHint(true);
}

private boolean isFragmentActive(Fragment target){
    return target.getUserVisibleHint();
}

如何在Android中保持像Instagram一样的片段状态？

2 个答案: