java - NullPointerException : Getting data from Database ((java. lang.String)' 在空对象引用上)

Question

我创建了一个数据库来存储 ExoPlayer 的搜索时间，所以当用户尝试播放相同的内容时，如果它在数据库中，那么它将要求用户恢复或重新开始，但得到 NullPointerException。
这是数据库:

public class DatabaseHelper extends SQLiteOpenHelper {

   private static final int DATABASE_VERSION = 1;
   private static final String DATABASE_NAME = "mydata.db";

   private static final String EPISODE_TABLE_NAME = "episode_data";

   public DatabaseHelper(Context context) {
       super(context, DATABASE_NAME, null, DATABASE_VERSION);
   }

   @Override
   public void onCreate(SQLiteDatabase db) {
       db.execSQL(CREATE_EPISODE_DATA_TABLE());
   }

   
   private String CREATE_EPISODE_DATA_TABLE() {
       return "CREATE TABLE IF NOT EXISTS episode_data (id TEXT,timestamp TEXT)";
   }

   @Override
   public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
       db.execSQL("DROP TABLE IF EXISTS episode_data");
       onCreate(db);
   }

   public String getEpisodeData(String string2) {
       SQLiteDatabase sQLiteDatabase = this.getReadableDatabase();
       StringBuilder stringBuilder = new StringBuilder();
       stringBuilder.append("SELECT * FROM episode_data WHERE id= ");
       stringBuilder.append(string2);
       Cursor cursor = sQLiteDatabase.rawQuery(stringBuilder.toString(), null);
       String string3 = null;
       if (cursor != null) {
           boolean bl = cursor.moveToLast();
           string3 = null;
           if (bl) {
               string3 = cursor.getString(cursor.getColumnIndex("timestamp"));
           }
           cursor.close();
       }
       return string3;
   }

   public long insertEpisodeData(String string2, String string3) {
       SQLiteDatabase sQLiteDatabase = this.getWritableDatabase();
       ContentValues contentValues = new ContentValues();
       contentValues.put("id", string2);
       contentValues.put("timestamp", string3);
       long l = sQLiteDatabase.replace(EPISODE_TABLE_NAME, null, contentValues);
       sQLiteDatabase.close();
       return l;
   }

}

它存储数据并崩溃的 Activity :

public class ShowsDetailsActivity extends AppCompatActivity {

    public String episodeid;
    DatabaseHelper databaseHelper;

    @Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_series_details);

       databaseHelper = new DatabaseHelper(this);

        // My rest of the code
   }

   public void iniMoviePlayerForEpisode(EpiModel epiModel,Context context){

       ShowsDetailsActivity.epiModel =epiModel;
       String type=epiModel.getServerType();
       
  if (type.equals("embed") || type.equals("vimeo") || type.equals("gdrive")){
           isVideo=false;
           initWeb(epiModel.getStreamURL());
       }else {
           isVideo=true;
           initVideoPlayer(epiModel.getStreamURL(),context,type);
       }

       }
   }

   public void setMediaUrlForTvSeries(String url, String season, String episod, String episode_id) {
       mediaUrl = url;
       this.season = season;
       this.episod = episod;
       this.episodeid = episode_id;
   }


   public void initVideoPlayer(String url, Context context, String type) {
       progressBar.setVisibility(VISIBLE);

       if (player != null) {
           player.release();
       }

       BandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();
       TrackSelection.Factory videoTrackSelectionFactory = new
               AdaptiveTrackSelection.Factory(bandwidthMeter);


       TrackSelector trackSelector = new
               DefaultTrackSelector(videoTrackSelectionFactory);

       player = ExoPlayerFactory.newSimpleInstance(context, trackSelector);

       simpleExoPlayerView.setPlayer(player);
       player.prepare(mediaSource, true, false);

       player.addListener(new Player.DefaultEventListener() {

           @Override
           public void onPlayerStateChanged(boolean playWhenReady, int playbackState) {

               if (playWhenReady && playbackState == Player.STATE_READY) {

                   isPlaying = true;
                   progressBar.setVisibility(View.GONE);

               } else if (playbackState == Player.STATE_READY) {

                   progressBar.setVisibility(View.GONE);
                   isPlaying = false;

                   if (player != null) {
                       StringBuilder stringBuilder = new StringBuilder();
                       stringBuilder.append("episode id: ");
                       stringBuilder.append(episodeid);
                       stringBuilder.append(" TimeStamp: ");
                       stringBuilder.append(player.getCurrentPosition() / 1000L);
                       databaseHelper.insertEpisodeData(episodeid, String.valueOf((long)player.getCurrentPosition()));
                   }

               } else if (playbackState == Player.STATE_BUFFERING) {
                   isPlaying = false;
                   progressBar.setVisibility(VISIBLE);

               } else {
                   isPlaying = false;

                   if (player != null) {
                       StringBuilder stringBuilder = new StringBuilder();
                       stringBuilder.append("episode id: ");
                       stringBuilder.append(episodeid);
                       stringBuilder.append(" TimeStamp: ");
                       stringBuilder.append(player.getCurrentPosition() / 1000L);
                       databaseHelper.insertEpisodeData(episodeid, String.valueOf((long)player.getCurrentPosition()));
                   }
               }

           }
       });

       String getPlayed = databaseHelper.getEpisodeData(episodeid);
       if (getPlayed != null) {
           showResumeAlert();
           return;
       }
       player.setPlayWhenReady(true);

   }

   private void showResumeAlert () {
       new AlertDialog.Builder(this)
               .setTitle("Do you want to resume from where you left ?")
               .setPositiveButton("Resume", new DialogInterface.OnClickListener() {
                   @Override
                   public void onClick(DialogInterface dialog, int which) {

                       String getPlayed = databaseHelper.getEpisodeData(episodeid);
                       if (getPlayed != null) {
                           player.seekTo(Long.parseLong(getPlayed));
                           player.setPlayWhenReady(true);
                       }
                   }
               })
               .setNegativeButton("Start Again", new DialogInterface.OnClickListener() {
                   @Override
                   public void onClick(DialogInterface dialog, int which) {
                       player.setPlayWhenReady(true);
                   }
               })
               .setCancelable(false)
               .show();
   }

    // My rest of the code

}

适配器:

public class DirectorApater extends RecyclerView.Adapter<DirectorApater.OriginalViewHolder> {

   private List<EpiModel> items;
   private Context ctx;

   int selectedPosition=-1;
   private int seasonNo;


   public DirectorApater(Context context, List<EpiModel> items,String name, int seasonNo) {
       ArrayList<EpiModel> arrayList=new ArrayList<>();
       for(int i=0;i<items.size();i++){
           if(items.get(i).getSeson().equals(name)){
               arrayList.add(items.get(i));
           }
       }

       items.clear();
       this.items = arrayList;
       this.seasonNo = seasonNo;

       ctx = context;
   }


   @Override
   public DirectorApater.OriginalViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
       DirectorApater.OriginalViewHolder vh;
       View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_director_name, parent, false);
       vh = new DirectorApater.OriginalViewHolder(v);
       return vh;
   }

   @Override
   public void onBindViewHolder(final DirectorApater.OriginalViewHolder holder, final int position) {
       final EpiModel obj = items.get(position);

       holder.llEpi.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               selectedPosition=position;
               notifyDataSetChanged();
               ((ShowsDetailsActivity)ctx).setMediaUrlForTvSeries(obj.getStreamURL(), obj.getSeson(), obj.getEpi(), obj.getEpisode_id());

 if (!castSession) {
                   new ShowsDetailsActivity().iniMoviePlayerForEpisode(obj,ctx);
               } else {
                   ((ShowsDetailsActivity)ctx).showQueuePopup(ctx, holder.llEpi, ((ShowsDetailsActivity)ctx).getMediaInfo());

               }
           }
       });

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

   public class OriginalViewHolder extends RecyclerView.ViewHolder {

       // some code

       public OriginalViewHolder(View v) {
           super(v);
            // some code
       }
   }

所以基本上当用户点击recyclerview项目时，它会将数据传递给 Activity 类“(ShowsDetailsActivity)ctx).setMediaUrlForTvSeries(obj.getStreamURL(), obj.getSeson(), obj.getEpi(), obj.getEpisode_id( ));"
应用程序可以正常工作

 String getPlayed = databaseHelper.getEpisodeData(episodeid);
        if (getPlayed != null) {
            showResumeAlert();
            return;
        }

在 ShowsDetailsActivity 类中，但是当我添加它时崩溃并显示此错误日志:

java.lang.NullPointerException: Attempt to invoke virtual method'java.lang.Stringcom.myapp.db.DatabaseHelper.getEpisodeData(java.lang.String)' on a null object reference

Answer 1

您调用iniMoviePlayerForEpisode方法在这里:

new ShowsDetailsActivity().iniMoviePlayerForEpisode(obj,ctx);

但那时 onCreate尚未调用，因此您的 databaseHelper仍然为空。检查我链接的引用: onCreate在您的 Activity 启动时调用，而不是在创建对象时调用。