RecyclerViewを使用していて、android.support.v7.widget.RecyclerView.setHasFixedSize（boolean）を呼び出すとアプリケーションがクラッシュする

Question

私はFragmentsとRecyclerViewでアプリケーションを構築しています。私はこれを行うには、チュートリアルのビルメッセージ断片一部を使用していTHIS TUTORIAL

：

私はこのチュートリアルを次しています。

しかし、私は、このエラーが発生します：

08-17 10:21:51.674 32646-32646/zca.zcaimobile E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: zca.zcaimobile, PID: 32646 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{zca.zcaimobile/zca.zcaimobile.activities.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2521) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2601) 
     at android.app.ActivityThread.access$800(ActivityThread.java:178) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470) 
     at android.os.Handler.dispatchMessage(Handler.java:111) 
     at android.os.Looper.loop(Looper.java:194) 
     at android.app.ActivityThread.main(ActivityThread.java:5637) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setHasFixedSize(boolean)' on a null object reference 
     at zca.zcaimobile.fragments.PaymentFragment.onViewCreated(PaymentFragment.java:43) 
     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1127) 
     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290) 
     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801) 
     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1677) 
     at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388) 
     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:604) 
     at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:178) 
     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1244) 
     at android.app.Activity.performStart(Activity.java:6116) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2478) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2601)  
     at android.app.ActivityThread.access$800(ActivityThread.java:178)  
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)  
     at android.os.Handler.dispatchMessage(Handler.java:111)  
     at android.os.Looper.loop(Looper.java:194)  
     at android.app.ActivityThread.main(ActivityThread.java:5637)  
     at java.lang.reflect.Method.invoke(Native Method)  
     at java.lang.reflect.Method.invoke(Method.java:372)  
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)  
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)  

マイPaymentFragment.java

package zca.zcaimobile.fragments; 

import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.Fragment; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.Toast; 

import retrofit2.Call; 
import retrofit2.Callback; 
import retrofit2.Response; 
import retrofit2.Retrofit; 
import retrofit2.converter.gson.GsonConverterFactory; 
import zca.zcaimobile.R; 
import zca.zcaimobile.api.APIService; 
import zca.zcaimobile.api.APIUrl; 
import zca.zcaimobile.helper.PaymentAdapter; 
import zca.zcaimobile.helper.SharedPrefManager; 
import zca.zcaimobile.models.Payments; 

public class PaymentFragment extends Fragment { 

    private RecyclerView recyclerViewMessages; 
    private RecyclerView.Adapter adapter; 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
     return inflater.inflate(R.layout.fragment_messages, container, false); 
    } 

    @Override 
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { 
     super.onViewCreated(view, savedInstanceState); 
     getActivity().setTitle("Messages"); 

     recyclerViewMessages = (RecyclerView) view.findViewById(R.id.recyclerViewMessages); 
     recyclerViewMessages.setHasFixedSize(true); 
     recyclerViewMessages.setLayoutManager(new LinearLayoutManager(getActivity())); 


     Retrofit retrofit = new Retrofit.Builder() 
       .baseUrl(APIUrl.BASE_URL) 
       .addConverterFactory(GsonConverterFactory.create()) 
       .build(); 

     APIService service = retrofit.create(APIService.class); 

     Call<Payments> call = service.getPayments(SharedPrefManager.getInstance(getActivity()).getUser().getId()); 

     call.enqueue(new Callback<Payments>() { 
      @Override 
      public void onResponse(Call<Payments> call, Response<Payments> response) { 
       adapter = new PaymentAdapter(response.body().getMessages(), getActivity()); 
       recyclerViewMessages.setAdapter(adapter); 
      } 

      @Override 
      public void onFailure(Call<Payments> call, Throwable t) { 
       Toast.makeText(getActivity(), t.getMessage(), Toast.LENGTH_LONG).show(); 
      } 
     }); 
    } 
} 

マイfragment_payment.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:orientation="vertical" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 

<android.support.v7.widget.RecyclerView 
    android:id="@+id/recyclerViewMessages" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content"> 

</android.support.v7.widget.RecyclerView> 

私はMessageFragmentを使用していますthの一部チュートリアルでは、PaymentFragment.javaの参照として、その部分と私のpaymentfragmentは同じ機能を持っているためです。

誰かが私を助けることができますか？私はAndroidプログラミングの初心者なので、何が起こっているのか分かりません。

ありがとうございます。

Answer 1

レイアウト名がfragment_payment.xmlでないのは、R.layout.fragment_messagesです。 LayoutInflaterはfragment_messages.xml

変更でこのrecyclerviewを見つけることができません。

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 
    return inflater.inflate(R.layout.fragment_payment, container, false); 
}