Android Studio自带的底部导航栏 实现从其他Activity跳转到MainActivity下的任意一个Fragment

总体思想：
可以先跳转到Fragment所在的MainActivity，再通过NavController控制跳转到指定的Fragment,就可以显示出来了

// 其他的Activity界面 (即你当前所在的Activity,你需要跳转到底部导航栏的任意一项(Fragment))
Intent intent = new Intent(Details.this, MainActivity.class);
// 设置需要跳转到底部导航栏项的标志(名称随意，数字也随意，对应即可)
intent.putExtra("fragment_flag",1);
startActivity(intent);

MainActivity代码：

public class MainActivity extends AppCompatActivity {
    NavController navController = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BottomNavigationView navView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications,R.id.navigation_search)
                .build();
        navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        NavigationUI.setupWithNavController(navView, navController);
    }

    @Override
    protected void onResume() {
        // 获取从其他Activity发送过来跳转Fragment的标志fragment_flag(名称随意)
        int fragmentFlag = this.getIntent().getIntExtra("fragment_flag", 0);
        switch (fragmentFlag){
            case 1:
                // 控制跳转到底部导航项(navigation_home为该Fragment的对应控件的id值)
                navController.navigate(R.id.navigation_home);
                break;
            case 2:
                navController.navigate(R.id.navigation_dashboard);
                break;
            case 3:
                navController.navigate(R.id.navigation_search);
                break;
            case 4:
                navController.navigate(R.id.navigation_cart);
                break;
            case 5:
                navController.navigate(R.id.navigation_notifications);
                break;
        }
        super.onResume();
    }
}

NavController用法参看

对应的fragment

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mobile_navigation"
    app:startDestination="@+id/navigation_home">

    <fragment
        android:id="@+id/navigation_home"
        android:name="com.gzpy.onlineretailerstest.ui.home.HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home" />

    <fragment
        android:id="@+id/navigation_dashboard"
        android:name="com.gzpy.onlineretailerstest.ui.dashboard.DashboardFragment"
        android:label="@string/title_dashboard"
        tools:layout="@layout/fragment_dashboard" />

    <fragment
        android:id="@+id/navigation_search"
        android:name="com.gzpy.onlineretailerstest.ui.search.SearchFragment"
        android:label="@string/title_search"
        tools:layout="@layout/fragment_dashboard" />

    <fragment
        android:id="@+id/navigation_cart"
        android:name="com.gzpy.onlineretailerstest.ui.cart.CartFragment"
        android:label="@string/title_cart"
        tools:layout="@layout/fragment_cart" />

    <fragment
        android:id="@+id/navigation_notifications"
        android:name="com.gzpy.onlineretailerstest.ui.notifications.NotificationsFragment"
        android:label="@string/title_notifications"
        tools:layout="@layout/fragment_notifications" />
</navigation>

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <!-- android:paddingTop="?attr/actionBarSize" 设置此属性顶部会出现空白-->


    <!--app:labelVisibilityMode="labeled"可以把文字显示出来-->
    <com.google.android.material.bottomnavigation.BottomNavigationView
        app:labelVisibilityMode="labeled"
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />


    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />


</androidx.constraintlayout.widget.ConstraintLayout>

item:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/navigation_home"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/title_home" />

    <item
        android:id="@+id/navigation_dashboard"
        android:icon="@drawable/ic_dashboard_black_24dp"
        android:title="@string/title_dashboard" />

    <item
        android:id="@+id/navigation_search"
        android:icon="@drawable/ic_search"
        android:title="@string/title_search" />

    <item
        android:id="@+id/navigation_cart"
        android:icon="@drawable/ic_cart"
        android:title="@string/title_cart" />

    <item
        android:id="@+id/navigation_notifications"
        android:icon="@drawable/ic_me"
        android:title="@string/title_notifications" />

</menu>

fragment:

public class HomeFragment extends Fragment {

//    private HomeViewModel homeViewModel;

    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
//        homeViewModel =  ViewModelProviders.of(this).get(HomeViewModel.class);
//        View root = inflater.inflate(R.layout.fragment_home, container, false);
//        final TextView textView = root.findViewById(R.id.text_home);
//        homeViewModel.getText().observe(this, new Observer() {
//            @Override
//            public void onChanged(@Nullable String s) {
//                textView.setText(s);
//            }
//        });

        View root = inflater.inflate(R.layout.fragment_home, container, false);
        listView = root.findViewById(R.id.listView);
        // 设置显示菜单
        setHasOptionsMenu(true);
        return root;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
}