android - 使用 navhost 在底部导航中停止 fragment 刷新

Question

这个问题已经被问过几次了，但是我们现在是 2020 年，有没有人找到一个很好的可用解决方案呢？

我希望能够使用底部导航控件进行导航，而无需在每次选择 fragment 时都刷新 fragment 。这是我目前拥有的:

导航/main.xml:

<?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/main"
    app:startDestination="@id/home">

    <fragment
        android:id="@+id/home"
        android:name="com.org.ftech.fragment.HomeFragment"
        android:label="@string/app_name"
        tools:layout="@layout/fragment_home" />
    <fragment
        android:id="@+id/news"
        android:name="com.org.ftech.fragment.NewsFragment"
        android:label="News"
        tools:layout="@layout/fragment_news"/>
    <fragment
        android:id="@+id/markets"
        android:name="com.org.ftech.fragment.MarketsFragment"
        android:label="Markets"
        tools:layout="@layout/fragment_markets"/>
    <fragment
        android:id="@+id/explore"
        android:name="com.org.ftech.ExploreFragment"
        android:label="Explore"
        tools:layout="@layout/fragment_explore"/>
</navigation>

Activity 邮件.xml:

<?xml version="1.0" encoding="utf-8"?>
<!-- Use DrawerLayout as root container for activity -->
<androidx.drawerlayout.widget.DrawerLayout
    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/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <fragment
            android:id="@+id/nav_host_fragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="0dp"
            android:layout_height="0dp"
            app:defaultNavHost="true"
            app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:navGraph="@navigation/main" />

        <com.google.android.material.bottomnavigation.BottomNavigationView
            android:id="@+id/bottomNavigationView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:itemIconTint="@color/nav"
            app:itemTextColor="@color/nav"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:menu="@menu/main">

        </com.google.android.material.bottomnavigation.BottomNavigationView>

    </androidx.constraintlayout.widget.ConstraintLayout>

    <com.google.android.material.navigation.NavigationView
        app:menu="@menu/main"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:id="@+id/navigationView"
        android:layout_gravity="start">
    </com.google.android.material.navigation.NavigationView>

</androidx.drawerlayout.widget.DrawerLayout>

MainActivity.kt:

class MainActivity : AppCompatActivity() {

    private var drawerLayout: DrawerLayout? = null
    private var navigationView: NavigationView? = null
    private var bottomNavigationView: BottomNavigationView? = null
    private lateinit var appBarConfiguration: AppBarConfiguration

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        drawerLayout = findViewById(R.id.drawer_layout)
        navigationView = findViewById(R.id.navigationView)
        bottomNavigationView = findViewById(R.id.bottomNavigationView)

        val navController = findNavController(R.id.nav_host_fragment)
        appBarConfiguration = AppBarConfiguration(setOf(R.id.markets, R.id.explore, R.id.news, R.id.home), drawerLayout)

        setupActionBarWithNavController(navController, appBarConfiguration)

        findViewById<NavigationView>(R.id.navigationView)
            .setupWithNavController(navController)

        findViewById<BottomNavigationView>(R.id.bottomNavigationView)
            .setupWithNavController(navController)

    }


    override fun onSupportNavigateUp(): Boolean {
        val navController = findNavController(R.id.nav_host_fragment)
        return navController.navigateUp(appBarConfiguration) || super.onSupportNavigateUp()
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        if (item.itemId == R.id.search) {
            startActivity(Intent(applicationContext, SearchableActivity::class.java))
        }
        return super.onOptionsItemSelected(item)
    }

    override fun onCreateOptionsMenu(menu: Menu?): Boolean {
        menuInflater.inflate(R.menu.options_menu, menu)
        return super.onCreateOptionsMenu(menu)
    }
}

在 fragment 中，我对我的服务进行了几次调用以获取 onCreateView 中的数据，当恢复 fragment 时，我假设这些调用将不再执行，并且应该保留 fragment 的状态。

Answer 1

尝试这个:

public class MainActivity extends AppCompatActivity {


    final Fragment fragment1 = new HomeFragment();
    final Fragment fragment2 = new DashboardFragment();
    final Fragment fragment3 = new NotificationsFragment();
    final FragmentManager fm = getSupportFragmentManager();
    Fragment active = fragment1;

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);


        BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);

        fm.beginTransaction().add(R.id.main_container, fragment3, "3").hide(fragment3).commit();
        fm.beginTransaction().add(R.id.main_container, fragment2, "2").hide(fragment2).commit();
        fm.beginTransaction().add(R.id.main_container,fragment1, "1").commit();

    }


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

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    fm.beginTransaction().hide(active).show(fragment1).commit();
                    active = fragment1;
                    return true;

                case R.id.navigation_dashboard:
                    fm.beginTransaction().hide(active).show(fragment2).commit();
                    active = fragment2;
                    return true;

                case R.id.navigation_notifications:
                    fm.beginTransaction().hide(active).show(fragment3).commit();
                    active = fragment3;
                    return true;
            }
            return false;
        }
    };


    @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);
    }


}

或者您可以按照谷歌推荐的解决方案: Google Link