不兼容的类型：RecViewFragment 无法转换为 Fragment

Question

早些时候，我的代码运行良好，但在 android studio gradle build 中进行了一些更新后，出现错误 - “错误：不兼容的类型：RecViewFragment 无法转换为 Fragment getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new RecViewFragment()).commit();" 我试过 import androidx.fragment.app.Fragment

import android.content.Intent;
import android.os.Bundle;
import android.view.MenuItem;

import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.fragment.app.Fragment;

import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.android.material.navigation.NavigationView;

public class MainActivityBuses extends AppCompatActivity {

NavigationView nav;
ActionBarDrawerToggle toggle;
DrawerLayout drawerLayout;
Toolbar toolbar;
BottomNavigationView btmNav;


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


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

nav = findViewById(R.id.drawernav);
drawerLayout = findViewById(R.id.drawerlayout);

toggle = new ActionBarDrawerToggle(this,drawerLayout, toolbar,R.string.open,R.string.close);
drawerLayout.addDrawerListener(toggle);
toggle.syncState();

nav.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        Fragment selectdnav = null;
        switch (item.getItemId()){
            case R.id.dnavprofile:
                selectdnav = new MyProfileFragment();
                drawerLayout.closeDrawer(GravityCompat.START);
                break;
            case R.id.dnavmap:
                selectdnav = new MapFragment();
                drawerLayout.closeDrawer(GravityCompat.START);
                break;
            case R.id.dnavmybus:
                selectdnav = new BusFragment();
                drawerLayout.closeDrawer(GravityCompat.START);
                break;
            case R.id.dnavinfo:
                selectdnav = new InfoFragment();
                drawerLayout.closeDrawer(GravityCompat.START);
                break;
        }
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,selectdnav).commit();
        return true;
    }
});

        btmNav = (BottomNavigationView) findViewById(R.id.btmnav);
        btmNav.setOnNavigationItemSelectedListener((navListner));
        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new RecViewFragment()).commit();
        btmNav.getMenu().findItem(R.id.navhome).setChecked(true);
    }
    private BottomNavigationView.OnNavigationItemSelectedListener navListner = new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            Fragment selectedFragment = null;
            switch (item.getItemId()){
                case R.id.navprofile:
                    selectedFragment = new MyProfileFragment();
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new MyProfileFragment()).commit();
                    break;
                case R.id.navmap:
                    Intent intent = new Intent(MainActivityBuses.this, MapActivity.class);
                    startActivity(intent);
                    finish();
                  

                    break;
                case R.id.navhome:
                    
                    selectedFragment = new RecViewFragment();
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new RecViewFragment()).commit();
                    break;
                case R.id.navmybus:
                   
                    selectedFragment = new BusFragment();
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new BusFragment()).commit();
                    break;
                case R.id.navinfo:
                   
                    selectedFragment = new InfoFragment();
                    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new InfoFragment()).commit();
                    break;
            }
          
            return true;
        }
    };


}

RecViewFragment 类

package com.example.trackmybusstudent;

import android.app.Fragment;
import android.os.Build;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.RequiresApi;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.Query;
import com.google.firebase.firestore.QuerySnapshot;

import java.util.ArrayList;
import java.util.List;

/**
 * A simple {@link Fragment} subclass.
 * Use the {@link RecViewFragment#newInstance} factory method to
 * create an instance of this fragment.
 */
public class RecViewFragment extends Fragment {
RecyclerView recyclerView;
ArrayList datalist;
FirebaseFirestore db;
myadapter myadap;

    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";


    private String mParam1;
    private String mParam2;

    public RecViewFragment() {
    }
    public static RecViewFragment newInstance(String param1, String param2) {
        RecViewFragment fragment = new RecViewFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    @RequiresApi(api = Build.VERSION_CODES.M)
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
       View v = inflater.inflate(R.layout.fragment_rec_view, container, false);
       recyclerView = (RecyclerView) v.findViewById(R.id.recycleview);
       recyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
       db = FirebaseFirestore.getInstance();
       datalist = new ArrayList<>();
       myadap = new myadapter(datalist);
       recyclerView.setAdapter(myadap);
       db.collection("Bus_Database").orderBy("Route_Number", Query.Direction.ASCENDING).get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
           @Override
           public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
               List<DocumentSnapshot> list = queryDocumentSnapshots.getDocuments();
               for(DocumentSnapshot d:list){
                   model obj = d.toObject(model.class);
                   datalist.add(obj);
                   myadap.notifyDataSetChanged();
               }
           }
       });
       return v;
    }
}

Answer 1

在您的开关中没有默认情况，也许您没有在菜单文件中正确设置您的 id，因此 selectdnav 保持为空。 建议你加个断点快速分析一下。