Java 应用程序因“而崩溃”；“空引用上的对象”；我不知道该怎么解决这个问题

我不断地得到错误，但我无法找到解决它的方法，因为一切似乎都是正确的。这很累，因为我看不出我的代码有任何问题。我真的希望有人能帮忙，我很困惑。我想制作一个音乐列表页面，使用recyclerview。我也有一个api

日志：

Process: com.anisacoding.expriment, PID: 24248
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
    at com.anisacoding.expriment.Adapter.SoundAdapter.getItemCount(SoundAdapter.java:58)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4044)
    at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3849)
    at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1762)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
    at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
    at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
    at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
    at com.android.internal.policy.DecorView.onLayout(DecorView.java:1041)
    at android.view.View.layout(View.java:22419)
    at android.view.ViewGroup.layout(ViewGroup.java:6584)
    at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3378)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2842)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1888)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8511)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
    at android.view.Choreographer.doCallbacks(Choreographer.java:761)
    at android.view.Choreographer.doFrame(Choreographer.java:696)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7050)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:965)

API接口：

import retrofit2.Call;
import retrofit2.http.GET;

public interface ApiInterface {
    /////getting all posts/////
    @GET("posts.php")
    Call<Users> performAllPosts();

    ///////getting all sounds//////

    @GET("sounds.php")
    Call<Users> performAllSounds();

}

用户：

import com.anisacoding.expriment.Model.MediaObject;
import com.anisacoding.expriment.Model.SoundModel;
import com.google.gson.annotations.SerializedName;

import java.util.ArrayList;

public class Users {

    @SerializedName("ALL_POSTS")
    private ArrayList<MediaObject> AllPosts;

    @SerializedName("All_SOUNDS")
    private ArrayList<SoundModel> AllSounds;


        public ArrayList<MediaObject> getAllPosts(){
        return AllPosts;
    }

    public ArrayList<SoundModel> getAllSounds(){
            return AllSounds;
    }
}

声音活动：

 private RecyclerView recyclerview;
    private List<SoundModel> soundModelList = new ArrayList<>();
    private SoundAdapter soundAdapter;
    public static ApiInterface apiInterface;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sound);

        apiInterface = ApiClient.getApiClient().create(ApiInterface.class);
        recyclerview = (RecyclerView) findViewById(R.id.recyclerview);
        LinearLayoutManager layoutManager3 = new LinearLayoutManager(this);
        layoutManager3.setOrientation(RecyclerView.VERTICAL);
        recyclerview.setLayoutManager(new GridLayoutManager(this, 2));

      Call<Users> call = apiInterface.performAllSounds();
      call.enqueue(new Callback<Users>() {
          @Override
          public void onResponse(Call<Users> call, Response<Users> response) {
              if (response.isSuccessful())
              {
                  soundModelList = response.body().getAllSounds();
                  soundAdapter = new SoundAdapter(soundModelList, getApplicationContext());
                  recyclerview.setAdapter(soundAdapter);
                  soundAdapter.notifyDataSetChanged();
              } else{
                  Toast.makeText(SoundActivity.this, "network error", Toast.LENGTH_SHORT).show();
              }
          }

          @Override
          public void onFailure(Call<Users> call, Throwable t) {
              Toast.makeText(SoundActivity.this, "network error", Toast.LENGTH_SHORT).show();

          }
      });    

    }
        public void backBtn (View view){
            Intent intent = new Intent(SoundActivity.this, PortraitCameraActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
            startActivity(intent);
            Animatoo.animateInAndOut(this);
            finish();
        }


        @Override
        public void onBackPressed () {
            Intent intent = new Intent(SoundActivity.this, PortraitCameraActivity.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
            startActivity(intent);
            Animatoo.animateInAndOut(this);
            finish();
        }

    }

私有回收视图回收视图；
私有列表soundModelList=new ArrayList（）；
专用声卡声卡；
公共静态接口；
@凌驾
创建时受保护的void（Bundle savedInstanceState）{
super.onCreate（savedInstanceState）；
setContentView（右布局、活动和声音）；
apiInterface=ApiClient.getApiClient（）.create（apiInterface.class）；
recyclerview=（recyclerview）findViewById（R.id.recyclerview）；
LinearLayoutManager LayoutManager 3=新的LinearLayoutManager（此）；
LayoutManager 3.设置方向（RecyclerView.垂直）；
setLayoutManager（新的GridLayoutManager（this，2））；
Call Call=apinterface.performAllSounds（）；
call.enqueue（新回调（）{
@凌驾
公共void onResponse（调用、响应）{
if（response.issusccessful（））
{
soundModelList=response.body（）.getAllSounds（）；
soundAdapter=新的soundAdapter（soundModelList，getApplicationContext（））；
recyclerview.setAdapter（声音适配器）；
soundAdapter.notifyDataSetChanged（）；
}否则{
Toast.makeText（SoundActivity.this，“网络错误”，Toast.LENGTH_SHORT.show（）；
}
}
@凌驾
失败时公共无效（调用调用，可丢弃的t）{
Toast.makeText（SoundActivity.this，“网络错误”，Toast.LENGTH_SHORT.show（）；
}
});    
}
公共void backBtn（视图）{
意向意向=新意向（SoundActivity.this、cameraActivity.class）；
intent.setFlags（intent.FLAG_ACTIVITY_NEW_TASK | intent.FLAG_ACTIVITY_CLEAR_TASK）；
星触觉（意向）；
Animatoo.animateInAndOut（这个）；
完成（）；
}
@凌驾
反压时的公共无效（）{
意向意向=新意向（SoundActivity.this、cameraActivity.class）；
intent.setFlags（intent.FLAG_ACTIVITY_NEW_TASK | intent.FLAG_ACTIVITY_CLEAR_TASK）；
星触觉（意向）；
Animatoo.animateInAndOut（这个）；
完成（）；
}
}

声音适配器：

import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;


import com.anisacoding.expriment.Model.SoundModel;
import com.anisacoding.expriment.R;
import com.anisacoding.expriment.VideoEditorFolder.PortraitCameraActivity;

import java.util.List;


public class SoundAdapter extends RecyclerView.Adapter<SoundAdapter.SoundViewHolder> {
    List<SoundModel> soundModelList;
    Context context;

    public SoundAdapter(List<SoundModel> soundModelList, Context context) {
        this.soundModelList = soundModelList;
        this.context = context;
    }

    @NonNull
    @Override
    public SoundViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.layout_sound, viewGroup, false);
        return new SoundViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull SoundViewHolder holder, int position) {

        SoundModel soundModel = soundModelList.get(position);
        holder.sound_title.setText(soundModel.getSound_title());

        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(context, PortraitCameraActivity.class);
                intent.putExtra("sound_url", soundModel.getSound_file());
                intent.putExtra("sound_title", soundModel.getSound_title());
                context.startActivity(intent);
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
            }
        });

    }

    @Override
    public int getItemCount() {
        return soundModelList.size();
    }


    public class SoundViewHolder extends RecyclerView.ViewHolder {

        private TextView sound_title;

        public SoundViewHolder(@NonNull View itemView) {
            super(itemView);

            sound_title = itemView.findViewById(R.id.music_title);
        }
    }
}

导入android.content.Context；
导入android.content.Intent；
导入android.view.LayoutInflater；
导入android.view.view；
导入android.view.ViewGroup；
导入android.widget.TextView；
导入androidx.annotation.NonNull；
导入androidx.recyclerview.widget.recyclerview；
导入com.anisacode.expriment.Model.SoundModel；
进口com.anisacoding.EXPLIMENT.R；
导入com.anisacode.expriment.VideoEditorFolder.cameraActivity；
导入java.util.List；
公共类SoundAdapter扩展了RecyclerView.Adapter{
列表声音模型列表；
语境；
公共SoundAdapter（列表soundModelList，上下文）{
this.soundModelList=soundModelList；
this.context=上下文；
}
@非空
@凌驾
public SoundViewHolder onCreateViewHolder（@NonNull ViewGroup ViewGroup，int viewType）{
View View=LayoutInflater.from（viewGroup.getContext（））.flate（R.layout.layout\u声音，viewGroup，false）；
返回新的SoundViewHolder（视图）；
}
@凌驾
公共无效onBindViewHolder（@NonNull SoundViewHolder holder，int位置）{
SoundModel SoundModel=soundModelList.get（位置）；
holder.sound_title.setText（soundModel.getSound_title（））；
holder.itemView.setOnClickListener（新视图.OnClickListener（）{
@凌驾
公共void onClick（视图）{
意向意向=新意向（上下文、活动类）；
intent.putExtra（“sound_url”，soundModel.getSound_file（））；
intent.putExtra（“sound_title”，soundModel.getSound_title（））；
背景。开始触觉（意图）；
intent.setFlags（intent.FLAG_ACTIVITY_NEW_TASK | intent.FLAG_ACTIVITY_CLEAR_TASK）；
}
});
}
@凌驾
public int getItemCount（）{
返回soundModelList.size（）；
}
公共类SoundViewHolder扩展了RecyclerView.ViewHolder{
私有文本视图声音标题；
公共SoundViewHolder（@NonNull View itemView）{
超级（项目视图）；
sound\u title=itemView.findviewbyd（R.id.music\u title）；
}
}
}

布局：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="8dp">


    <ImageView
        android:id="@+id/imageView20"
        android:layout_width="157dp"
        android:layout_height="141dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="8dp"
        android:contentDescription="@string/library_music"
        app:tint="#000000"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_library_music" />

    <TextView
        android:id="@+id/music_title"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:maxLength="50"
        android:text="Alaf file song ......."
        android:textColor="@android:color/white"
        android:textSize="12sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="@+id/imageView20"
        app:layout_constraintStart_toStartOf="@+id/imageView20"
        app:layout_constraintTop_toBottomOf="@+id/imageView20"
        app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:background="@android:color/white"
    tools:context=".Activities.SoundActivity">

    <ImageView
        android:id="@+id/cross"
        android:layout_width="43dp"
        android:layout_height="43dp"
        android:layout_marginTop="4dp"
        android:contentDescription="@string/cross"
        android:onClick="backBtn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_cross" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="408dp"
        android:layout_height="730dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

布局：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="8dp">


    <ImageView
        android:id="@+id/imageView20"
        android:layout_width="157dp"
        android:layout_height="141dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="8dp"
        android:contentDescription="@string/library_music"
        app:tint="#000000"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_library_music" />

    <TextView
        android:id="@+id/music_title"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:maxLength="50"
        android:text="Alaf file song ......."
        android:textColor="@android:color/white"
        android:textSize="12sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="@+id/imageView20"
        app:layout_constraintStart_toStartOf="@+id/imageView20"
        app:layout_constraintTop_toBottomOf="@+id/imageView20"
        app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:background="@android:color/white"
    tools:context=".Activities.SoundActivity">

    <ImageView
        android:id="@+id/cross"
        android:layout_width="43dp"
        android:layout_height="43dp"
        android:layout_marginTop="4dp"
        android:contentDescription="@string/cross"
        android:onClick="backBtn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/ic_cross" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerview"
        android:layout_width="408dp"
        android:layout_height="730dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />
</androidx.constraintlayout.widget.ConstraintLayout>

---

错误本身说明：

java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
    at com.anisacoding.expriment.Adapter.SoundAdapter.getItemCount(SoundAdapter.java:58)

因此，您应该查看您的

SoundAdapter.getItemCount

，在那里使用

List.size（）

时会得到一个NPE。

---

在这种情况下，请确保初始化列表！=）

为什么

@SerializedName（“ALL_POSTS”）

是大写的，而

@SerializedName（“ALL_SOUNDS”）

是小写的

l

而不是“ALL”这个词中的

l

？您得到的NullPointerException是因为

AllSounds

-列表是

null

。所以序列化失败了，我认为这与那些小写字母有关。但是我不太熟悉

com.google.gson.annotations

的

@SerializedName

注释是如何工作的，所以也许我弄错了。我太爱你了❤️ , 成功了。