java - 如何通过单击抽屉导航 Activity 中的后退按钮从其他 fragment 返回特定 fragment

Question

我知道之前在这里讨论过这个主题，但没有一个对我的代码有用。我做了什么:

在 Home.java(抽屉导航主 Activity )中将其用于抽屉导航功能

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {

    int id = item.getItemId();
    Fragment fragment = null;
    Class fragmentClass = null;

    if (id == R.id.nav_breakfast) {
        fragmentClass = Breakfast.class;
    } else if (id == R.id.nav_lunch) {
        fragmentClass = Lunch.class;
    } else if (id == R.id.nav_wallet) {
        fragmentClass = Wallet.class;
    } else if (id == R.id.nav_history) {
        fragmentClass = History.class;
    } else if (id == R.id.nav_reset) {
        fragmentClass = ResetPass.class;
    } else if (id == R.id.nav_send) {
        fragmentClass = ContactUs.class;
    } else if (id == R.id.nav_help) {
        fragmentClass = Help.class;
    } else if (id == R.id.nav_about) {
        fragmentClass = AboutUs.class;
    }

    try {
        assert fragmentClass != null;
        fragment = (Fragment) fragmentClass.newInstance();
    } catch (Exception e) {
        e.printStackTrace();
    }

    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).addToBackStack(null).commit();

    drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    assert drawer != null;
    drawer.closeDrawer(GravityCompat.START);

    return true;
}

通过单击抽屉导航项目选择打开每个声明的 fragment 。另一方面，我还创建了另一个 fragment ，该 fragment 设置为在 Home Activity 实际开始时默认打开

 if (savedInstanceState == null) {
        Fragment fragment = null;
        Class fragmentClass;
        fragmentClass = AllProduct.class;
        try {
            fragment = (Fragment) fragmentClass.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
        }

        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

在 onBackPressed() 上我使用了这个:

@Override
public void onBackPressed() {
    if (drawer.isDrawerOpen(GravityCompat.START)) {
        drawer.closeDrawer(GravityCompat.START);
    }
    else if (getSupportFragmentManager().getBackStackEntryCount() > 0) {
        getSupportFragmentManager().popBackStack();
    }
    else if (doubleBackToExitPressedOnce) {
        super.onBackPressed();
    }
    else {
        this.doubleBackToExitPressedOnce = true;
        Toast.makeText(this, "Press again to exit", Toast.LENGTH_SHORT).show();

        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                doubleBackToExitPressedOnce = false;
            }
        }, 2000);
    }

所有的 fragment Activity 都是这样编码的:

public class AllProduct extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_all_product, container, false);

    return view;
}

@Override
public void onResume() {
    super.onResume();
    getActivity().setTitle(R.string.app_name);
}

现在一切正常，只有一个问题。假设我想从抽屉导航中打开 Fragment [1](不是上面提到的默认 fragment )，然后再次打开抽屉导航并打开 Fragment [2]，然后是 Fragment [3]。现在假设我在 Fragment [3] 中，按下后退按钮我直接想转到上面提到的默认 fragment 。它首先转到 fragment [2]、 fragment [1]，然后是默认 fragment 。但我想要无论何时何地，在哪个 fragment 中，我都必须通过按下后退按钮返回到默认 fragment 。

Answer 1

就用

getSupportFragmentManager()
    .beginTransaction()
    .replace(...)
    .addToBackStack("tag").commit()

并删除所有其他代码，尤其是 onBackPressed() 中的代码