BottomNavigationView NavHostFragment我不想每次选择选项卡时都从数据服务器读取片段

问题描述

当从“帖子”选项卡单击“个人资料”选项卡单击服务器时，我不想从服务器调用该信息，而我又返回到“帖子”选项卡，并且我不想再次进行刷新。

>

如果我再次处于“发帖”标签中，则我不想刷新该信息。 我不希望在“帖子”选项卡中，选择“个人资料”选项卡并返回“帖子”选项卡时刷新页面 当我从服务器收到新信息时，我想秘密更新帖子列表 像WhatsApp一样，每个片段中的信息都是实时的

此代码与名为Fragment_Posts的Fragment Post选项卡有关，该选项卡从服务器接收帖子并在recyclerview中显示它们

public class Fragment_Posts extends Fragment {
    public FragmentPostsBinding binding;
    public viewmodel_Posts vm_psots;
    Adapter_posts adapter_posts;

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

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
        Log.e(TAG,"onCreateView: posts");
        binding = DataBindingUtil.inflate(inflater,R.layout.fragment_posts,container,false);
        vm_psots = new viewmodelProvider(this).get(viewmodel_Posts.class);
        vm_psots.Post();
        vm_psots.listmutablelivedata_posts.observe(requireActivity(),new Observer<List<Model_Post>>() {
            @Override
            public void onChanged(List<Model_Post> model_posts) {
                binding.recycleviewFrgposts.setLayoutManager(new linearlayoutmanager(requireActivity()));
                adapter_posts = new Adapter_posts(model_posts);
                binding.recycleviewFrgposts.setAdapter(adapter_posts);
            }
        });
        return binding.getRoot();
    }


}

public class MainActivity extends AppCompatActivity implements BottomNavigationView.OnNavigationItemSelectedListener {
    private static final String TAG = "MainActivity";
    ActivityMainBinding binding;
    NavHostFragment navHostFragment;
    NavController navController;
    AppBarConfiguration appBarConfiguration;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //getSupportActionBar().hide();
        binding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        appBarConfiguration = new AppBarConfiguration.Builder(R.navigation.navigation).build();
        navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.fragment_main);
        //If the inequality is null,run the line
        assert navHostFragment != null;
        navController = navHostFragment.getNavController();
        binding.botnavMain.setonNavigationItemSelectedListener(this);

    }

    //That we can work with our fragment stack
    @Override
    public boolean onSupportNavigateUp() {
        return NavigationUI.navigateUp(navController,appBarConfiguration);
    }


    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
        switch (menuItem.getItemId()) {
            case R.id.menu_home:
                    navController.navigate(R.id.fragment_Posts);
                break;
            case R.id.menu_cart:
                    navController.navigate(R.id.fragment_Cart);
                break;
            case R.id.menu_profile:
                    navController.navigate(R.id.fragment_Profile);
                break;
        }
        return false;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<layout  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">
<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <!--If the user presses the back button,do not leave the app
            app:defaultNavHost="true"-->
    <fragment
        android:id="@+id/fragment_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        android:layout_above="@+id/botnav_main"
        app:navGraph="@navigation/navigation" />
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/botnav_main"
        android:layout_alignParentBottom="true"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        app:menu="@menu/menu"
        app:itemTextColor="?colorAccent"
        app:itemIconTint="?colorAccent"
        />
</RelativeLayout>


</layout>

解决方法

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