如何在啟動 android 應用程序時啟動特定片段

Question

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.viewpager.widget.ViewPager;

import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.view.MenuItem;
import android.view.View;
import android.view.WindowManager;

import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.firebase.auth.FirebaseAuth;

public class MainActivity extends AppCompatActivity {

    BottomNavigationView bottomNavigationView;
    Fragment selectedFragment =  null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        try
        {
            this.getSupportActionBar().hide();
        }
        catch (NullPointerException e){}

        setContentView(R.layout.activity_main);

        bottomNavigationView = (BottomNavigationView)
                findViewById(R.id.bottom_navigation);

        bottomNavigationView.setOnNavigationItemSelectedListener(
                new BottomNavigationView.OnNavigationItemSelectedListener() {


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

                        switch (item.getItemId()) {
                            case R.id.homee:
                                selectedFragment = new HomeFragment();
                                break;
                            case R.id.nav_search:
                                selectedFragment = new SearchFragment();
                                break;

                            case R.id.nav_notif:
                                selectedFragment = null;
                                startActivity(new Intent(MainActivity.this ,SearchFragment.class));
                                break;
                        }

                        if (selectedFragment != null){
                            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container, selectedFragment).commit();
                        }

                    return true;
                }
        });

    }

}

這都是我的主要活動代碼......我應該怎么做，當用戶進入應用程序時，默認情況下會按照此代碼打開主頁片段，當用戶進入應用程序時，他需要按下主頁按鈕才能進入片段...我如何默認情況下，例如 instagram，一旦用戶進入它，它將用戶留在主頁片段我怎么能，我使用 android 材料底部導航如果你問我也可以提供此活動的 xml 文件..謝謝你

Answer 1

設置setOnNavigationItemSelectedListener后嘗試此代碼

bottomNavigationView.getMenu().findItem(R.id. homee).setChecked(true)

Answer 2

在您的 MainActivity onCreate 方法中嘗試此操作。

FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.fragment_container, new ExploreMainFragment());
        ft.commit();