在回收站項目中獲取空指針異常單擊偵聽器接口

Question

我知道這個問題非常多，但是我搜索了很多，我無法理解這個問題。我創建一個接口，用於回收視圖上的特定貨物處理點擊聽衆

這裏是我的班

MovieAdapter.java

package com.example.vikas.movie.adapter; 

/** 
* Created by vikas on 23/4/17. 
*/ 
import android.content.Context; 
import android.support.v7.widget.RecyclerView; 
import android.text.TextUtils; 
import android.util.Log; 
import android.view.HapticFeedbackConstants; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.RelativeLayout; 
import android.widget.TextView; 

import com.bumptech.glide.Glide; 
import com.bumptech.glide.load.engine.DiskCacheStrategy; 
import com.example.vikas.movie.R; 
import com.example.vikas.movie.helper.CircleTransformation; 
import com.example.vikas.movie.model.Movie; 

import java.util.List; 
public class MovieAdapter extends RecyclerView.Adapter<MovieAdapter.MovieViewHolder> 
{ 
    private static final String TAG=MovieAdapter.class.getSimpleName(); 

    private List<Movie> movies; 
    private int rowLayout; 
    private Context context; 
    private MovieAdapterListener listener; 


    public static class MovieViewHolder extends RecyclerView.ViewHolder 
    { 
     RelativeLayout moviesLayout; 
     TextView movieTitle; 
     TextView data; 
     TextView movieDescription; 
     TextView rating; 
     ImageView imageView; 


     public MovieViewHolder(View v) 
     { 
      super(v); 
      moviesLayout = (RelativeLayout) v.findViewById(R.id.movie_layout); 
      movieTitle = (TextView) v.findViewById(R.id.title); 
      data = (TextView) v.findViewById(R.id.subtitle); 
      movieDescription = (TextView) v.findViewById(R.id.description); 
      rating = (TextView) v.findViewById(R.id.rating); 
      imageView=(ImageView)v.findViewById(R.id.movie_image); 
     } 



    } 

    public MovieAdapter(List<Movie> movies, int rowLayout, Context context) 
    { 
     this.movies = movies; 
     this.rowLayout = rowLayout; 
     this.context = context; 
    } 

    @Override 
    public MovieAdapter.MovieViewHolder onCreateViewHolder(ViewGroup parent, 
                  int viewType) 
    { 
     View view = LayoutInflater.from(parent.getContext()).inflate(rowLayout, parent, false); 
     return new MovieViewHolder(view); 
    } 


    @Override 
    public void onBindViewHolder(MovieViewHolder holder, final int position) 
    { 
     Movie movie= movies.get(position); 
     holder.movieTitle.setText(movies.get(position).getTitle()); 
     holder.data.setText(movies.get(position).getReleaseDate()); 
     holder.movieDescription.setText(movies.get(position).getOverview()); 
     holder.rating.setText(movies.get(position).getvote_average().toString()); 
     MovieImage(holder,movie); 
     applyClickEvents(holder,position); 


    } 
    private void applyClickEvents(MovieViewHolder holder,final int position) 
    { 
     holder.moviesLayout.setOnClickListener(new View.OnClickListener() 
     { 
      @Override 
      public void onClick(View view) 
      { 
       listener.onItemClicked(position); 
      } 
     }); 


    } 


    private void MovieImage(MovieViewHolder holder,Movie movie) 
    { 
     String base_URL="https://image.tmdb.org/t/p/"; 
     String size_Image="w500"; 
     String file_Path=movie.getPosterPath(); 

     StringBuilder image_Path=new StringBuilder(); 
     image_Path.append(base_URL).append(size_Image).append(file_Path); 
     Log.d(TAG,"movie genere ids "+movie.getGenreIds()); 
     Log.d(TAG,"movie relese date "+movie.getReleaseDate()); 




     if(!TextUtils.isEmpty(image_Path)) 
     { 
      Glide.with(context).load(image_Path.toString()) 
        .thumbnail(0.5f) 
        .crossFade() 
        .transform(new CircleTransformation(context)) 
        .diskCacheStrategy(DiskCacheStrategy.ALL) 
        .into(holder.imageView); 
     } 
     else 
     { 
      holder.imageView.setImageResource(R.drawable.circle); 
     } 

    } 

    public interface MovieAdapterListener 
    { 
     void onItemClicked(int position); 

    } 


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

MainActivity.java在我implenting接口和重寫我在界面中聲明的方法。

package com.example.vikas.movie.activity; 

import android.support.design.widget.CoordinatorLayout; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.DefaultItemAnimator; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.util.Log; 
import android.widget.Toast; 


import com.example.vikas.movie.R; 
import com.example.vikas.movie.adapter.MovieAdapter; 
import com.example.vikas.movie.model.Movie; 
import com.example.vikas.movie.model.MoviesResponse; 
import com.example.vikas.movie.rest.ApiClient; 
import com.example.vikas.movie.rest.ApiInterface; 

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

import retrofit2.Call; 
import retrofit2.Callback; 
import retrofit2.Response; 

public class MainActivity extends AppCompatActivity implements MovieAdapter.MovieAdapterListener 
{ 

    private static final String TAG=MainActivity.class.getSimpleName(); 
    //get which got from web API 
    private final static String API_KEY="xxxxx"; 
    private CoordinatorLayout coordinatorLayout; 
    // private MovieAdapter movieAdapter; 
    private RecyclerView recyclerView; 
    private List<Movie> movieList = new ArrayList<>(); 

    @Override 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     coordinatorLayout=(CoordinatorLayout)findViewById(R.id.coordinate_layout); 

     if(API_KEY.isEmpty()) 
     { 
      Snackbar snackbar = Snackbar 
        .make(coordinatorLayout, "Please Enter The key", Snackbar.LENGTH_LONG); 

      snackbar.show(); 
      return; 
     } 
     recyclerView = (RecyclerView) findViewById(R.id.recycler_view); 
     recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext())); 
     recyclerView.setItemAnimator(new DefaultItemAnimator()); 



     ApiInterface apiInterface= ApiClient.getClient().create(ApiInterface.class); 
     Call<MoviesResponse> call= apiInterface.getNowPlayingMovies(API_KEY); 
     call.enqueue(new Callback<MoviesResponse>() 
     { 
      @Override 
      public void onResponse(Call<MoviesResponse> call, Response<MoviesResponse> response) 
      { 

       movieList= response.body().getResults(); 
       Log.d(TAG, "Number of movies received: " + movieList.size()); 
       recyclerView.setAdapter(new MovieAdapter(movieList, R.layout.recyclerview_item_movie, getApplicationContext())); 
       // movieAdapter.notifyDataSetChanged(); 
       // Log.d(TAG, "Number of movies received: " + movieList.); 


      } 

      @Override 
      public void onFailure(Call<MoviesResponse> call, Throwable t) 
      { 
       Snackbar snackbar = Snackbar 
         .make(coordinatorLayout, "Please Check your Internet Connection", Snackbar.LENGTH_LONG); 

       snackbar.show(); 
       Log.e(TAG, t.toString()); 

      } 
     }); 

    } 

    @Override 
    public void onItemClicked(int position) 
    { 
     Movie movie = movieList.get(position); 
     movie.getGenreIds(); 
     movie.getId(); 
     Toast.makeText(getApplicationContext(), "id: "+ movie.getId(), Toast.LENGTH_SHORT).show(); 
    } 


} 

我得到的logcat這樣

FATAL EXCEPTION: main 
                     Process: com.example.vikas.movie, PID: 23565 
                     java.lang.NullPointerException: Attempt to invoke interface method 'void com.example.vikas.movie.adapter.MovieAdapter$MovieAdapterListener.onItemClicked(int)' on a null object reference 
                      at com.example.vikas.movie.adapter.MovieAdapter$1.onClick(MovieAdapter.java:97) 
                      at android.view.View.performClick(View.java:5205) 
                      at android.view.View$PerformClick.run(View.java:21164) 
                      at android.os.Handler.handleCallback(Handler.java:739) 
                      at android.os.Handler.dispatchMessage(Handler.java:95) 
                      at android.os.Looper.loop(Looper.java:148) 
                      at android.app.ActivityThread.main(ActivityThread.java:5417) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
04-26 23:56:00.538 23565-23565/com.example.vikas.movie I/Process: Sending signal. PID: 23565 SIG: 9 

請人幫忙，我無法理解的問題。

Answer 1

你得到NullPointerException我你的界面監聽器。

在適配器類初始化你的界面聽衆：

public MovieAdapter(List<Movie> movies, int rowLayout, Context context) { 
    this.movies = movies; 
    this.rowLayout = rowLayout; 
    this.context = context; 
    listener = (MovieAdapterListener) context; //add this 

} 

編輯

而且現在設置使用適配器：

recyclerView.setAdapter(new MovieAdapter(movieList, R.layout.recyclerview_item_movie, MainActivity.this)); 

Answer 2

發生這種情況是因爲您尚未初始化「聽衆」。當您在MainActivity中創建新的MovieAdapter並將其分配給「偵聽器」時，必須傳遞偵聽器。

在MovieAdapter.java，改變公衆MovieAdapter（）到

public MovieAdapter(List<Movie> movies, int rowLayout, Context context, MovieAdapterListener listener) 
{ 
    this.movies = movies; 
    this.rowLayout = rowLayout; 
    this.context = context; 
    this.listener=listener; 
} 

和MainActivity.java， 改線

recyclerView.setAdapter(new MovieAdapter(movieList, R.layout.recyclerview_item_movie, getApplicationContext())); 

到

recyclerView.setAdapter(new MovieAdapter(movieList, R.layout.recyclerview_item_movie, getApplicationContext(),listener)); 
//change "listener into the name of MovieAdapterListener object" 

Answer 3

我相信MovieAdapter應該初始化監聽成員：

public MovieAdapter(List<Movie> movies, int rowLayout, Context context, MovieAdapterListener lstn) 
{ 
    this.movies = movies; 
    this.rowLayout = rowLayout; 
    this.context = context; 
    this.listener = lstn; 
} 

而且在MainActivity當你設置適配器，因爲它實現MovieAdapter.MovieAdapterListener你應該通過它的另一個實例：

recyclerView.setAdapter(new MovieAdapter(movieList, R.layout.recyclerview_item_movie, this, this));