如何在 Fragment 中使用 Recycler View [重复]
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【中文标题】如何在 Fragment 中使用 Recycler View [重复]【英文标题】：How to Use Recycler View in Fragment [duplicate] 【发布时间】：2021-07-19 02:04:12 【问题描述】：马斯塔
我正在尝试从我的 FireBase 实时数据库中读取数据。我在 Fragment 中使用 Recycler 视图来阅读它。当我编码时，没有错误的迹象。但是当我尝试运行代码时，它会显示如下错误：
2021-04-25 20:37:21.060 20896-20896/com.kuplay.storingdata E/androidRuntime: FATAL EXCEPTION: main
Process: com.kuplay.storingdata, PID: 20896
java.lang.ClassCastException: com.kuplay.storingdata.ui.MainActivity cannot be cast to com.kuplay.storingdata.Adapter.RecyclerViewAdapter$dataListener
at com.kuplay.storingdata.Adapter.RecyclerViewAdapter.<init>(RecyclerViewAdapter.java:39)
at com.kuplay.storingdata.Fragment.data.DataFragment$1.onDataChange(DataFragment.java:80)
at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75)
at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:239)
at android.app.ActivityThread.main(ActivityThread.java:8179)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:626)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1015)
我尝试了很多方法并尝试从谷歌搜索许多参考。但它不起作用。
任何机构都可以帮我解决这个错误...因为我还是个菜鸟。
这是我的代码：
DataFragment.java
package com.kuplay.storingdata.Fragment.data;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.core.content.ContextCompat;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.DividerItemDecoration;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.kuplay.storingdata.Adapter.RecyclerViewAdapter;
import com.kuplay.storingdata.Model.data_finance;
import com.kuplay.storingdata.R;
import org.jetbrains.annotations.NotNull;
import java.util.ArrayList;
import java.util.Objects;
public class DataFragment extends Fragment
private RecyclerView recyclerView;
private RecyclerViewAdapter adapter;
private RecyclerView.LayoutManager layoutManager;
private FirebaseAuth auth;
private DatabaseReference reference;
private ArrayList<data_finance> dFinance;
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
View root = inflater.inflate(R.layout.fragment_data, container, false);
recyclerView = root.findViewById(R.id.data_list);
auth = FirebaseAuth.getInstance();
MyRecyclerView();
GetData();
return root;
private void MyRecyclerView()
layoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
DividerItemDecoration itemDecoration = new DividerItemDecoration(getActivity(), DividerItemDecoration.VERTICAL);
itemDecoration.setDrawable(Objects.requireNonNull(ContextCompat.getDrawable(getActivity(), R.drawable.line)));
recyclerView.addItemDecoration(itemDecoration);
private void GetData()
reference = FirebaseDatabase.getInstance().getReference();
reference.child("Finance");
reference.child(Objects.requireNonNull(auth.getUid()));
reference.child("Data");
reference.addValueEventListener(new ValueEventListener()
@Override
public void onDataChange(@NotNull DataSnapshot dataSnapshot)
//Inisialisasi ArrayList
dFinance = new ArrayList<>();
for (DataSnapshot snapshot : dataSnapshot.getChildren())
data_finance finance = snapshot.getValue(data_finance.class);
assert finance != null;
finance.setId(snapshot.getKey());
dFinance.add(finance);
adapter = new RecyclerViewAdapter(dFinance, getActivity());
recyclerView.setAdapter(adapter);
@Override
public void onCancelled(@NotNull DatabaseError databaseError)
Toast.makeText(getActivity(), "Data Gagal Dimuat", Toast.LENGTH_LONG).show();
Log.e("MyListActivity", databaseError.getDetails() + " " + databaseError.getMessage());
);
RecyclerViewAdapter.java
package com.kuplay.storingdata.Adapter;
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import androidx.appcompat.app.AlertDialog;
import androidx.recyclerview.widget.RecyclerView;
import com.kuplay.storingdata.Model.data_finance;
import com.kuplay.storingdata.R;
import com.kuplay.storingdata.ui.updateData;
import org.jetbrains.annotations.NotNull;
import java.util.ArrayList;
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder>
private ArrayList<data_finance> listFinance;
private Context context;
public interface dataListener
void onDeleteData(data_finance data, int position);
dataListener listener;
public RecyclerViewAdapter(ArrayList<data_finance> listFinance, Context context)
this.listFinance = listFinance;
this.context = context;
listener = (dataListener) context;
static class ViewHolder extends RecyclerView.ViewHolder
private TextView Nama;
private TextView Pemasukan;
private TextView Pengeluaran;
private TextView Waktu;
private LinearLayout lst_item;
ViewHolder(View itemView)
super(itemView);
Nama = itemView.findViewById(R.id.tbl_nama);
Pemasukan = itemView.findViewById(R.id.tbl_pemasukan);
Pengeluaran = itemView.findViewById(R.id.tbl_pengeluaran);
Waktu = itemView.findViewById(R.id.tbl_waktu);
LinearLayout tbl_header = itemView.findViewById(R.id.tbl_header);
lst_item = itemView.findViewById(R.id.lst_item);
@NotNull
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
View V = LayoutInflater.from(parent.getContext()).inflate(R.layout.view_design, parent, false);
return new ViewHolder(V);
@SuppressLint("SetTextI18n")
@Override
public void onBindViewHolder(ViewHolder holder, final int position)
final String Nama = listFinance.get(position).getNama();
final String Pemasukan = listFinance.get(position).getPemasukan();
final String Pengeluaran = listFinance.get(position).getPengeluaran();
final String Waktu = listFinance.get(position).getWaktu();
holder.Nama.setText(Nama);
holder.Pemasukan.setText(Pemasukan);
holder.Pengeluaran.setText(Pengeluaran);
holder.Waktu.setText(Waktu);
holder.lst_item.setOnLongClickListener(new View.OnLongClickListener()
@Override
public boolean onLongClick(final View view)
final String[] action = "Update", "Delete";
AlertDialog.Builder alert = new AlertDialog.Builder(view.getContext());
alert.setItems(action, new DialogInterface.OnClickListener()
@Override
public void onClick(DialogInterface dialog, int i)
switch (i)
case 0:
Bundle bundle = new Bundle();
bundle.putString("dataNama", listFinance.get(position).getNama());
bundle.putString("dataPemasukan", listFinance.get(position).getPemasukan());
bundle.putString("dataPengeluaran", listFinance.get(position).getPengeluaran());
bundle.putString("dataWaktu", listFinance.get(position).getWaktu());
bundle.putString("getPrimaryKey", listFinance.get(position).getId());
Intent intent = new Intent(view.getContext(), updateData.class);
intent.putExtras(bundle);
context.startActivity(intent);
break;
case 1:
listener.onDeleteData(listFinance.get(position), position);
break;
);
alert.create();
alert.show();
return true;
);
@Override
public int getItemCount()
return listFinance.size();
MainActivity.java
package com.kuplay.storingdata.ui;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.view.MenuItem;
import android.view.View;
import android.view.Menu;
import android.widget.Toast;
import com.firebase.ui.auth.AuthUI;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;
import com.google.android.material.navigation.NavigationView;
import com.google.firebase.auth.FirebaseAuth;
import com.kuplay.storingdata.Fragment.input.InputFragment;
import com.kuplay.storingdata.R;
import androidx.annotation.NonNull;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
public class MainActivity extends AppCompatActivity
private AppBarConfiguration mAppBarConfiguration;
public FirebaseAuth auth;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
DrawerLayout drawer = findViewById(R.id.drawer_layout);
NavigationView navigationView = findViewById(R.id.nav_view);
mAppBarConfiguration = new AppBarConfiguration.Builder(
R.id.nav_input, R.id.nav_data, R.id.nav_cashflow)
.setDrawerLayout(drawer)
.build();
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
NavigationUI.setupWithNavController(navigationView, navController);
@Override
public boolean onCreateOptionsMenu(Menu menu)
getMenuInflater().inflate(R.menu.main, menu);
return true;
@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item)
switch (item.getItemId())
case R.id.logout:
AuthUI.getInstance()
.signOut(this)
.addOnCompleteListener(new OnCompleteListener()
@Override
public void onComplete(@NonNull Task task)
Toast.makeText(MainActivity.this, "Logout Berhasil", Toast.LENGTH_SHORT).show();
Intent home = new Intent(MainActivity.this, StartActivity.class);
startActivity(home);
finish();
);
return true;
return false;
@Override
public boolean onSupportNavigateUp()
NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
return NavigationUI.navigateUp(navController, mAppBarConfiguration)
|| super.onSupportNavigateUp();
请有人帮我解决这个错误；(
【问题讨论】：
【参考方案1】： adapter = new RecyclerViewAdapter(dFinance, getActivity());
你在 RecyclerViewAdapter 中设置上下文变量，我看到的就是 MainActivity (getActivity())。
public RecyclerViewAdapter(ArrayList<data_finance> listFinance, Context context)
this.listFinance = listFinance;
this.context = context;
listener = (dataListener) context;
在这里，您尝试将上下文 (MainActivity) 转换为 dataListener 类型，这是错误“java.lang.ClassCastException: com.kuplay.storingdata.ui.MainActivity 无法转换为 com.kuplay”所指示的不匹配.storingdata.Adapter.RecyclerViewAdapter$dataListener"
你不能让 MainActivity 像 in 那样实现 dataListener 吗？
class MainActivity ... implements RecyclerViewAdapter.dataListener
然后简单地覆盖接口函数？
【讨论】：
【参考方案2】：MainActivity 没有实现 MainActivity dataListener 接口，但是您正在将活动投射到适配器中的 dataListener ，这实际上是错误的。您可以在 MainActivity 或 Fragment 中实现 dataListener 并传递实际参数。
【讨论】：
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