尝试在空对象引用上调用虚方法 'android.content.res.Resources android.content.Context.getResources()' 什么问题

Question

我想运行点击项目时发出声音但点击项目时显示错误图片和文字正确但点击项目播放声音报错照片和 cobe 编号 48 中的鞋子错误吗

BabListAdapter
package com.example.learnn.ui;

import android.content.Context;
import android.media.MediaPlayer;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import com.example.learnn.EnglishlettersActivity;
import com.example.learnn.R;

import java.util.ArrayList;

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

public class BabyListAdapter extends RecyclerView.Adapter<BabyListAdapter.BabyViewHolder> {
    private MediaPlayer mMediaPlayer;
    Context context;


    private ArrayList<BabyModel> letterList = new ArrayList<>();

    public BabyListAdapter() {
        this.context = context;

    }

    @NonNull
    @Override
    public BabyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new BabyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.litter_list_item, parent, false));
    }




    @Override
    public void onBindViewHolder(@NonNull BabyViewHolder holder, final int position) {
        holder.image.setImageResource(letterList.get(position).getLetterRecourceID());
        holder.text.setText (letterList.get(position).getDefaultText());
        holder.part.setOnClickListener ( new View.OnClickListener () {
            @Override
            public void onClick(View v) {
                mMediaPlayer = MediaPlayer.create ( context,letterList.get ( position ).getAudioResourceId () );
                mMediaPlayer.start();
            }
        } );

    }

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


    public void setList(ArrayList<BabyModel> letterList) {
        this.letterList = letterList;
        notifyDataSetChanged();
    }

    public class BabyViewHolder extends RecyclerView.ViewHolder {
        ImageView image;
        TextView text;
        LinearLayout part;


        public BabyViewHolder(@NonNull View itemView) {
            super(itemView);
            image = itemView.findViewById(R.id.imagee);
            text = itemView.findViewById(R.id.text);
            part = itemView.findViewById(R.id.part);
        }

    }


}






EnglishLetterActivity
package com.example.learnn;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.TextView;

import com.example.learnn.databinding.ActivityEnglishcolorsBinding;
import com.example.learnn.databinding.ActivityEnglishlettersBinding;
import com.example.learnn.ui.BabyListAdapter;
import com.example.learnn.ui.BabyModel;
import com.example.learnn.ui.BabyViewModel;

import java.util.ArrayList;

public class EnglishlettersActivity extends AppCompatActivity {

    BabyViewModel babyViewModel;
    ImageView imagee,next;
    RecyclerView recycler;
    private int index = 0;
    private  MediaPlayer mMediaPlayer;
    ArrayList arrayList,letterList;
    Context context;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityEnglishlettersBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_englishletters);

        imagee = (ImageView)findViewById(R.id.imagee);
        recycler = (RecyclerView)findViewById(R.id.recycler);



        final BabyListAdapter adapter = new BabyListAdapter();
        recycler.setAdapter(adapter);
        GridLayoutManager layoutManager = new GridLayoutManager ( this, 3 );
        recycler.setLayoutManager(layoutManager);

        babyViewModel = ViewModelProviders.of(this).get(BabyViewModel.class);
        babyViewModel.letterRecourceIDMutableLiveData.observe(this, new Observer<ArrayList<BabyModel>>() {
            @Override
            public void onChanged(ArrayList<BabyModel> babyModels) {
                adapter.setList(babyModels);

            }
        });
        babyViewModel.getLetterRecourceID();









    }


}

BabyViewModel
package com.example.learnn.ui;

import com.example.learnn.R;

import java.util.ArrayList;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class BabyViewModel extends ViewModel {

    ArrayList arrayList;

    public MutableLiveData<ArrayList<BabyModel>> letterRecourceIDMutableLiveData = new MutableLiveData<>();
    public MutableLiveData<ArrayList<BabyModel>> defaultTextMutableLiveData = new MutableLiveData<>();
    public MutableLiveData<ArrayList<BabyModel>> audioResourceIdMutableLiveData = new MutableLiveData<>();


    public void getLetterRecourceID(){
        letterRecourceIDMutableLiveData.setValue(getDataFromDatabase());
     }

    public void getDefaultText(){
     defaultTextMutableLiveData.setValue(getDataFromDatabase());
    }
    public void getAudioResourceId(){
        audioResourceIdMutableLiveData.setValue(getDataFromDatabase());
    }

     private ArrayList<BabyModel> getDataFromDatabase(){
        ArrayList<BabyModel> arrayList = new ArrayList<>();
         arrayList.add(new BabyModel(R.drawable.a, "A",R.raw.a));
         arrayList.add(new BabyModel(R.drawable.b,"B",R.raw.b));
         arrayList.add(new BabyModel(R.drawable.c,"D",R.raw.c));
         arrayList.add(new BabyModel(R.drawable.d,"D",R.raw.d));
         arrayList.add(new BabyModel(R.drawable.e,"E",R.raw.e));
         arrayList.add(new BabyModel(R.drawable.f,"F",R.raw.f));
         arrayList.add(new BabyModel(R.drawable.g,"G",R.raw.g));
         arrayList.add(new BabyModel(R.drawable.h,"H",R.raw.h));
         arrayList.add(new BabyModel(R.drawable.i,"I",R.raw.i));
         arrayList.add(new BabyModel(R.drawable.j,"J",R.raw.j));
         arrayList.add(new BabyModel(R.drawable.k,"K",R.raw.k));
         arrayList.add(new BabyModel(R.drawable.l,"L",R.raw.l));
         arrayList.add(new BabyModel(R.drawable.m,"M",R.raw.m));
         arrayList.add(new BabyModel(R.drawable.o,"O",R.raw.o));
         arrayList.add(new BabyModel(R.drawable.p,"P",R.raw.p));
         arrayList.add(new BabyModel(R.drawable.q,"G",R.raw.g));
         arrayList.add(new BabyModel(R.drawable.r,"R",R.raw.r));
         arrayList.add(new BabyModel(R.drawable.s,"S",R.raw.s));
         arrayList.add(new BabyModel(R.drawable.t,"T",R.raw.t));
         arrayList.add(new BabyModel(R.drawable.u,"U",R.raw.u));
         arrayList.add(new BabyModel(R.drawable.v,"U",R.raw.u));
         arrayList.add(new BabyModel(R.drawable.e,"E",R.raw.e));
         arrayList.add(new BabyModel(R.drawable.w,"W",R.raw.w));
         arrayList.add(new BabyModel(R.drawable.x,"X",R.raw.x));
         arrayList.add(new BabyModel(R.drawable.y,"Y",R.raw.y));
         arrayList.add(new BabyModel(R.drawable.z,"Z",R.raw.z));
         return arrayList;
    }
}




listlitteritem
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    >

    <data>

    </data>


       <FrameLayout
           android:layout_width="wrap_content"
           android:layout_height="wrap_content">



            <LinearLayout
                android:id="@+id/part"
                android:orientation="vertical"
                android:background="@drawable/letter_style"
                android:layout_margin="5dp"
                android:layout_width="120dp"
                android:layout_height="150dp">

                <ImageView
                    android:gravity="center"
                    android:id="@+id/imagee"
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:layout_weight="5"
                    android:layout_marginTop="15dp"
                    android:layout_marginRight="15dp"
                    android:layout_marginLeft="15dp"
                    tools:context=".EnglishlettersActivity" />

                <TextView
                    android:gravity="center_horizontal"
                    android:id="@+id/text"
                    android:textSize="20sp"
                    android:textStyle="bold"
                    android:textColor="#141414"
                    android:text="ddfdfdfdf"
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:layout_weight="1"
                    android:layout_marginBottom="10dp"
                     />
            </LinearLayout>
       </FrameLayout>

</layout>







BabListAdapter

package com.example.learnn.ui;

import android.content.Context;
import android.media.MediaPlayer;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import com.example.learnn.EnglishlettersActivity;
import com.example.learnn.R;
import java.util.ArrayList;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

public class BabyListAdapter extends RecyclerView.Adapter<BabyListAdapter.BabyViewHolder> {
    private MediaPlayer mMediaPlayer;
    Context context;

    private ArrayList<BabyModel> letterList = new ArrayList<>();

    public BabyListAdapter() {
        this.context = context;
    }

    @NonNull
    @Override
    public BabyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new BabyViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.litter_list_item, parent, false));
    }


    @Override
    public void onBindViewHolder(@NonNull BabyViewHolder holder, final int position) {
        holder.image.setImageResource(letterList.get(position).getLetterRecourceID());
        holder.text.setText (letterList.get(position).getDefaultText());
        holder.part.setOnClickListener ( new View.OnClickListener () {
            @Override
            public void onClick(View v) {
                mMediaPlayer = MediaPlayer.create ( context,letterList.get ( position ).getAudioResourceId () );
                mMediaPlayer.start();
            }
        } );
    }

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

    public void setList(ArrayList<BabyModel> letterList) {
        this.letterList = letterList;
        notifyDataSetChanged();
    }
    public class BabyViewHolder extends RecyclerView.ViewHolder {
        ImageView image;
        TextView text;
        LinearLayout part;

        public BabyViewHolder(@NonNull View itemView) {
            super(itemView);
            image = itemView.findViewById(R.id.imagee);
            text = itemView.findViewById(R.id.text);
            part = itemView.findViewById(R.id.part);
        }
    }

}






EnglishLetterActivity
package com.example.learnn;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.TextView;

import com.example.learnn.databinding.ActivityEnglishcolorsBinding;
import com.example.learnn.databinding.ActivityEnglishlettersBinding;
import com.example.learnn.ui.BabyListAdapter;
import com.example.learnn.ui.BabyModel;
import com.example.learnn.ui.BabyViewModel;

import java.util.ArrayList;

public class EnglishlettersActivity extends AppCompatActivity {

    BabyViewModel babyViewModel;
    ImageView imagee,next;
    RecyclerView recycler;
    private int index = 0;
    private  MediaPlayer mMediaPlayer;
    ArrayList arrayList,letterList;
    Context context;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ActivityEnglishlettersBinding binding = DataBindingUtil.setContentView(this, R.layout.activity_englishletters);

        imagee = (ImageView)findViewById(R.id.imagee);
        recycler = (RecyclerView)findViewById(R.id.recycler);



        final BabyListAdapter adapter = new BabyListAdapter();
        recycler.setAdapter(adapter);
        GridLayoutManager layoutManager = new GridLayoutManager ( this, 3 );
        recycler.setLayoutManager(layoutManager);

        babyViewModel = ViewModelProviders.of(this).get(BabyViewModel.class);
        babyViewModel.letterRecourceIDMutableLiveData.observe(this, new Observer<ArrayList<BabyModel>>() {
            @Override
            public void onChanged(ArrayList<BabyModel> babyModels) {
                adapter.setList(babyModels);

            }
        });
        babyViewModel.getLetterRecourceID();









    }


}

BabyViewModel
package com.example.learnn.ui;

import com.example.learnn.R;

import java.util.ArrayList;

import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class BabyViewModel extends ViewModel {

    ArrayList arrayList;

    public MutableLiveData<ArrayList<BabyModel>> letterRecourceIDMutableLiveData = new MutableLiveData<>();
    public MutableLiveData<ArrayList<BabyModel>> defaultTextMutableLiveData = new MutableLiveData<>();
    public MutableLiveData<ArrayList<BabyModel>> audioResourceIdMutableLiveData = new MutableLiveData<>();


    public void getLetterRecourceID(){
        letterRecourceIDMutableLiveData.setValue(getDataFromDatabase());
     }

    public void getDefaultText(){
     defaultTextMutableLiveData.setValue(getDataFromDatabase());
    }
    public void getAudioResourceId(){
        audioResourceIdMutableLiveData.setValue(getDataFromDatabase());
    }

     private ArrayList<BabyModel> getDataFromDatabase(){
        ArrayList<BabyModel> arrayList = new ArrayList<>();
         arrayList.add(new BabyModel(R.drawable.a, "A",R.raw.a));
         arrayList.add(new BabyModel(R.drawable.b,"B",R.raw.b));
         arrayList.add(new BabyModel(R.drawable.c,"D",R.raw.c));
         arrayList.add(new BabyModel(R.drawable.d,"D",R.raw.d));
         arrayList.add(new BabyModel(R.drawable.e,"E",R.raw.e));
         arrayList.add(new BabyModel(R.drawable.f,"F",R.raw.f));
         arrayList.add(new BabyModel(R.drawable.g,"G",R.raw.g));
         arrayList.add(new BabyModel(R.drawable.h,"H",R.raw.h));
         arrayList.add(new BabyModel(R.drawable.i,"I",R.raw.i));
         arrayList.add(new BabyModel(R.drawable.j,"J",R.raw.j));
         arrayList.add(new BabyModel(R.drawable.k,"K",R.raw.k));
         arrayList.add(new BabyModel(R.drawable.l,"L",R.raw.l));
         arrayList.add(new BabyModel(R.drawable.m,"M",R.raw.m));
         arrayList.add(new BabyModel(R.drawable.o,"O",R.raw.o));
         arrayList.add(new BabyModel(R.drawable.p,"P",R.raw.p));
         arrayList.add(new BabyModel(R.drawable.q,"G",R.raw.g));
         arrayList.add(new BabyModel(R.drawable.r,"R",R.raw.r));
         arrayList.add(new BabyModel(R.drawable.s,"S",R.raw.s));
         arrayList.add(new BabyModel(R.drawable.t,"T",R.raw.t));
         arrayList.add(new BabyModel(R.drawable.u,"U",R.raw.u));
         arrayList.add(new BabyModel(R.drawable.v,"U",R.raw.u));
         arrayList.add(new BabyModel(R.drawable.e,"E",R.raw.e));
         arrayList.add(new BabyModel(R.drawable.w,"W",R.raw.w));
         arrayList.add(new BabyModel(R.drawable.x,"X",R.raw.x));
         arrayList.add(new BabyModel(R.drawable.y,"Y",R.raw.y));
         arrayList.add(new BabyModel(R.drawable.z,"Z",R.raw.z));
         return arrayList;
    }
}




listlitteritem
<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    >

    <data>

    </data>


       <FrameLayout
           android:layout_width="wrap_content"
           android:layout_height="wrap_content">



            <LinearLayout
                android:id="@+id/part"
                android:orientation="vertical"
                android:background="@drawable/letter_style"
                android:layout_margin="5dp"
                android:layout_width="120dp"
                android:layout_height="150dp">

                <ImageView
                    android:gravity="center"
                    android:id="@+id/imagee"
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:layout_weight="5"
                    android:layout_marginTop="15dp"
                    android:layout_marginRight="15dp"
                    android:layout_marginLeft="15dp"
                    tools:context=".EnglishlettersActivity" />

                <TextView
                    android:gravity="center_horizontal"
                    android:id="@+id/text"
                    android:textSize="20sp"
                    android:textStyle="bold"
                    android:textColor="#141414"
                    android:text="ddfdfdfdf"
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:layout_weight="1"
                    android:layout_marginBottom="10dp"
                     />
            </LinearLayout>
       </FrameLayout>

</layout>

Answer 1

在您的适配器中所做的更改

public BabyListAdapter(Context context) {
    this.context = context;
}

在你的activity

BabyListAdapter adapter = new BabyListAdapter(EnglishlettersActivity.this);

Answer 2

尝试从 View v 获取上下文，如下所示

mMediaPlayer = MediaPlayer.create ( v.getContext(),letterList.get ( position ).getAudioResourceId () );

而不是

mMediaPlayer = MediaPlayer.create ( context,letterList.get ( position ).getAudioResourceId () );

尝试在空对象引用上调用虚方法 'android.content.res.Resources android.content.Context.getResources()' 什么问题

Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference whate problem

android

adapter

mvvm

android-studio

android-recyclerview