无法从数据库获取数据用户

问题描述：

我使用Ormlite来使用database.I通过firebaseId编写函数搜索用户。此功能获取有关用户：全名，电子邮件，照片的信息。但是，当去做姿态的活动我apliaction停止无法从数据库获取数据用户

ProfileActivity.class

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_profile); 
     Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 
     getSupportActionBar().setDisplayHomeAsUpEnabled(true); 
     ButterKnife.bind(this); 

     dbHelper = new DbHelper(this); 

     Application application = (Application) getApplicationContext(); 
     userFirebaseId = application.getFirebaseId(); 
//show line error 
     userMy = dbHelper.getByUser(userFirebaseId); 

     nameEditText.setText(userMy.getFullName()); 
     emailEditText.setText(userMy.getEmail()); 


     auth = FirebaseAuth.getInstance(); 
     user = FirebaseAuth.getInstance().getCurrentUser(); 
     authListener = new FirebaseAuth.AuthStateListener() { 
      @Override 
      public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) { 
       if (user == null) { 
        startActivity(new Intent(ProfileActivity.this, LoginActivity.class)); 
        finish(); 
       } 
      } 
     }; 
    }

DbHepler.class

公共类DbHelper扩展OrmLiteSqliteOpenHelper { PreparedQuery PQ;

Dao<User, ?> userDao=null; 
    Dao<MyDream, ?> myDreamDao = null; 

    public static final String DB_NAME = "dream.db"; 
    public static final int DB_VERSION = 1; 

    public DbHelper(Context context) { 
     super(context, DB_NAME, null, DB_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase database, ConnectionSource connectionSource) { 

     try { 
      TableUtils.createTable(connectionSource, Dream.class); 
      TableUtils.createTable(connectionSource, User.class); 
      TableUtils.createTable(connectionSource, MyDream.class); 
      Dao<Dream, Integer> dreamDao = getDao(Dream.class); 
      userDao = getDao(User.class); 
      myDreamDao = getDao(MyDream.class); 
      } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 


    @Override 
    public void onUpgrade(SQLiteDatabase database, ConnectionSource connectionSource, int oldVersion, int newVersion) { 
     try { 
      TableUtils.dropTable(connectionSource, Dream.class, true); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 


    public User getByUser(String firebaseId) { 
// this error line 
     QueryBuilder<User, ?> qb = userDao.queryBuilder(); 
     try { 
      qb.where().eq(User.Columns.FIREBASE_ID, firebaseId); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 


     try { 
      pq = qb.prepare(); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 


     try { 
      return userDao.queryForFirst(pq); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
     return null; 
    } 
    }

我的日志

FATAL EXCEPTION: main 
Process: magdalena.pl.dreamguide, PID: 11813 
                    java.lang.RuntimeException: Unable to start activity ComponentInfo{magdalena.pl.dreamguide/magdalena.pl.dreamguide.activity.ProfileActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'com.j256.ormlite.stmt.QueryBuilder com.j256.ormlite.dao.Dao.queryBuilder()' on a null object reference 
                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416) 
                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                     at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                     at android.os.Handler.dispatchMessage(Handler.java:102) 
                     at android.os.Looper.loop(Looper.java:148) 
                     at android.app.ActivityThread.main(ActivityThread.java:5417) 
                     at java.lang.reflect.Method.invoke(Native Method) 
                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
                     Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'com.j256.ormlite.stmt.QueryBuilder com.j256.ormlite.dao.Dao.queryBuilder()' on a null object reference 
                     at magdalena.pl.dreamguide.db.DbHelper.getByUser(DbHelper.java:460) 
                     at magdalena.pl.dreamguide.activity.ProfileActivity.onCreate(ProfileActivity.java:99) 
                     at android.app.Activity.performCreate(Activity.java:6251) 
                     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) 
                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) 
                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)  
                     at android.app.ActivityThread.-wrap11(ActivityThread.java)  
                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)  
                     at android.os.Handler.dispatchMessage(Handler.java:102)  
                     at android.os.Looper.loop(Looper.java:148)  
                     at android.app.ActivityThread.main(ActivityThread.java:5417)  
                     at java.lang.reflect.Method.invoke(Native Method)  
                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)  
                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

答

您初始化userDao内onCreate方法。只有在解释here时创建数据库时才会调用此方法。因此，初始化userDao的代码应该更接近它的使用情况，或者它在使用前被执行的地方。

无法从数据库获取数据用户

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