設置2 SQLOpenHelper拋出錯誤表

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我試圖重建我的databaseHandler，因爲我需要使用2個表。設置2 SQLOpenHelper拋出錯誤表

我跟着這裏給出了答案：Multiple Table SQLite DB Adapter(s) in Android?但是這是給我了以下問題：Attempt to invoke virtual method 'android.database.Cursor android.database.sqlite.SQLiteDatabase.rawQuery(java.lang.String, java.lang.String[])' on a null object reference

我將把我的DatabaseAdapter，我的DatabaseReminderHandler下文：

DatabaseAdapter：

package avappmobile.mytasks.DBHandlers; 

import android.content.Context; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

/** 
* Created by Alexandre on 02/03/2015. 
*/ 
public class DatabaseAdapter { 

    public static final String DATABASE_NAME = "myTasks"; 

    public static final int DATABASE_VERSION = 1; 

    private static final String TABLE_TASKS = "tasks", 
      KEY_TASK_ID = "id", 
      KEY_TITLE = "title", 
      KEY_YEAR = "year", 
      KEY_MONTH = "month", 
      KEY_DAY = "day", 
      KEY_HOUR = "hour", 
      KEY_MINUTE = "minute", 
      KEY_DATE = "date", 
      KEY_TIME = "time", 
      KEY_EVENT_ID = "eventid"; 

    private static final String TABLE_REMINDERS = "reminders", 
      KEY_REM_ID = "id", 
      KEY_DESC = "description", 
      KEY_ACTIVE = "active", 
      KEY_REM_HOUR = "hour", 
      KEY_REM_MINUTE = "minute", 
      KEY_DURATION = "duration"; 


    private final Context context; 
    private DatabaseHelper DBHelper; 
    private SQLiteDatabase db; 

    /** 
    * Constructor 
    * @param ctx 
    */ 
    public DatabaseAdapter(Context ctx) 
    { 
     this.context = ctx; 
     this.DBHelper = new DatabaseHelper(this.context); 
    } 

    private static class DatabaseHelper extends SQLiteOpenHelper 
    { 
     DatabaseHelper(Context context) 
     { 
      super(context, DATABASE_NAME, null, DATABASE_VERSION); 
     } 

     @Override 
     public void onCreate(SQLiteDatabase db) 
     { 
      db.execSQL("CREATE TABLE " + TABLE_TASKS + "(" + KEY_TASK_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_TITLE + " TEXT," + 
        KEY_YEAR + " TEXT," + KEY_MONTH + " TEXT," + KEY_DAY + " TEXT," + KEY_HOUR + " TEXT," + KEY_MINUTE + " TEXT," + 
        KEY_DATE + " TEXT," + KEY_TIME + " TEXT," + KEY_EVENT_ID + " TEXT)"); 

      db.execSQL("CREATE TABLE " + TABLE_REMINDERS + "(" + KEY_REM_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_DESC + " TEXT," + 
        KEY_ACTIVE + " TEXT," + KEY_REM_HOUR + " TEXT," + KEY_REM_MINUTE + " TEXT," + KEY_DURATION + " TEXT)"); 
     } 

     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, 
           int newVersion) 
     { 
      // Adding any table mods to this guy here 
     } 
    } 

    /* 
    * open the db 
    * @return this 
    * @throws SQLException 
    * return type: DBAdapter 
    */ 
    public DatabaseAdapter open() throws SQLException 
    { 
     this.db = this.DBHelper.getWritableDatabase(); 
     return this; 
    } 

    /** 
    * close the db 
    * return type: void 
    */ 
    public void close() 
    { 
     this.DBHelper.close(); 
    } 
}

DatabaseReminderHandler：

package avappmobile.mytasks.DBHandlers; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteOpenHelper; 

import java.sql.SQLException; 
import java.util.ArrayList; 
import java.util.List; 

import avappmobile.mytasks.Objects.Reminder; 

/** 
* Created by Alexandre on 01/03/2015. 
*/ 
public class DatabaseReminderHandler { 
/* 
    private static final int DATABASE_VERSION = 1; 

    private static final String DATABASE_NAME = "myTasks", 
      TABLE_REMINDERS = "reminders", 
      KEY_ID = "id", 
      KEY_DESC = "description", 
      KEY_ACTIVE = "active", 
      KEY_HOUR = "hour", 
      KEY_MINUTE = "minute", 
      KEY_DURATION = "duration"; 
*/ 
    private static final String ID = "id"; 
    private static final String DESC = "description"; 
    private static final String ACTIVE = "active"; 
    private static final String HOUR = "hour"; 
    private static final String MINUTE = "minute"; 
    private static final String DURATION = "duration"; 

    private static final String DATABASE_TABLE = "reminders"; 

    private DatabaseHelper mDbHelper; 
    private SQLiteDatabase mDb; 

    private final Context mCtx; 

    private static class DatabaseHelper extends SQLiteOpenHelper { 

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

     @Override 
     public void onCreate(SQLiteDatabase db) { 
     } 

     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     } 
    } 

    public DatabaseReminderHandler(Context context) { 
     //super(context, DATABASE_NAME, null, DATABASE_VERSION); 
     this.mCtx = context; 
    } 

    public DatabaseReminderHandler open() throws SQLException { 
     this.mDbHelper = new DatabaseHelper(this.mCtx); 
     this.mDb = this.mDbHelper.getWritableDatabase(); 
     return this; 
    } 

    public void close(){ 
     this.mDbHelper.close(); 
    } 
/* 
    @Override 
    public void onCreate(SQLiteDatabase db) { 
     db.execSQL("CREATE TABLE " + TABLE_REMINDERS + "(" + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," + KEY_DESC + " TEXT," + 
       KEY_ACTIVE + " TEXT," + KEY_HOUR + " TEXT," + KEY_MINUTE + " TEXT," + KEY_DURATION + " TEXT)"); 
    } 

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

     onCreate(db); 
    } 
*/ 
    public void createReminder(Reminder reminder) { 

     ContentValues values = new ContentValues(); 

     values.put(DESC, reminder.getDescription()); 
     values.put(ACTIVE, reminder.getActive()); 
     values.put(HOUR, reminder.getHour()); 
     values.put(MINUTE, reminder.getMinute()); 
     values.put(DURATION, reminder.getDuration()); 

     this.mDb.insert(DATABASE_TABLE, null, values); 
    } 

    public Reminder getReminder(int id) { 
     Cursor cursor = this.mDb.query(DATABASE_TABLE, new String[] { ID, DESC, ACTIVE, HOUR, MINUTE, DURATION }, ID + "=?", new String[] { String.valueOf(id) }, null, null, null, null); 

     if (cursor != null) 
      cursor.moveToFirst(); 

     Reminder reminder = new Reminder(Integer.parseInt(cursor.getString(0)), cursor.getString(1), Boolean.valueOf(cursor.getString(2)), Integer.parseInt(cursor.getString(3)), 
       Integer.parseInt(cursor.getString(4)), Integer.parseInt(cursor.getString(5))); 

     return reminder; 
    } 

    public Reminder getReminder(String description) { 
     Cursor cursor = this.mDb.query(DATABASE_TABLE, new String[] { ID, DESC, ACTIVE, HOUR, MINUTE, DURATION }, DESC + "=?", new String[] { description }, null, null, null, null); 

     if (cursor != null) 
      cursor.moveToFirst(); 

     Reminder reminder = new Reminder(Integer.parseInt(cursor.getString(0)), cursor.getString(1), Boolean.valueOf(cursor.getString(2)), Integer.parseInt(cursor.getString(3)), 
       Integer.parseInt(cursor.getString(4)), Integer.parseInt(cursor.getString(5))); 

     return reminder; 
    } 

    public int getRemindersCount() { 
     Cursor cursor = this.mDb.rawQuery("SELECT * FROM " + DATABASE_TABLE, null); 
     int count = cursor.getCount(); 

     return count; 
    } 

    public int getActiveReminders() { 
     Cursor cursor = this.mDb.rawQuery("SELECT * FROM " + DATABASE_TABLE + "WHERE active = 'true'", null); 
     int count = cursor.getCount(); 

     return count; 
    } 

    public List<Reminder> getActiveListReminders() { 
     List<Reminder> reminders = new ArrayList<Reminder>(); 

     Cursor cursor = this.mDb.rawQuery("SELECT * FROM " + DATABASE_TABLE + "WHERE active = 'true'", null); 

     if (cursor.moveToFirst()) { 
      do { 
       reminders.add(new Reminder(Integer.parseInt(cursor.getString(0)), cursor.getString(1), Boolean.valueOf(cursor.getString(2)), Integer.parseInt(cursor.getString(3)), 
         Integer.parseInt(cursor.getString(4)), Integer.parseInt(cursor.getString(5)))); 
      } 
      while (cursor.moveToNext()); 
     } 

     return reminders; 
    } 

    public int updateReminder(Reminder reminder) { 
     ContentValues values = new ContentValues(); 

     values.put(DESC, reminder.getDescription()); 
     values.put(ACTIVE, reminder.getActive()); 
     values.put(HOUR, reminder.getHour()); 
     values.put(MINUTE, reminder.getMinute()); 
     values.put(DURATION, reminder.getDuration()); 

     int rowsAffected = this.mDb.update(DATABASE_TABLE, values, ID + "=" + reminder.getId(), null); 

     return rowsAffected; 
    } 

    public List<Reminder> getAllReminders() { 
     List<Reminder> reminders = new ArrayList<Reminder>(); 

     Cursor cursor = this.mDb.rawQuery("SELECT * FROM " + DATABASE_TABLE, null); 

     if (cursor.moveToFirst()) { 
      do { 
       reminders.add(new Reminder(Integer.parseInt(cursor.getString(0)), cursor.getString(1), Boolean.valueOf(cursor.getString(2)), Integer.parseInt(cursor.getString(3)), 
         Integer.parseInt(cursor.getString(4)), Integer.parseInt(cursor.getString(5)))); 
      } 
      while (cursor.moveToNext()); 
     } 

     return reminders; 
    } 

    public void initReminders(Context context){ 
     int count = this.getRemindersCount(); 

     if(count == 0){ 

      // Create the 3 reminders 
      Reminder rem1 = new Reminder(count, "REMINDER_1", true, 0, 5, 5); 
      Reminder rem2 = new Reminder(count + 1, "REMINDER_2", true, 1, 0, 60); 
      Reminder rem3 = new Reminder(count + 2, "REMINDER_3", true, 24, 0, 1440); 

      this.createReminder(rem1); 
      this.createReminder(rem2); 
      this.createReminder(rem3); 
     } 
    } 
}

我也把我的mainActivity（HomePage.class），從那裏我初始化我的變量，並開始使用它們：

首頁（僅一分一部分，而不是全部的話）：

public class HomePage extends ActionBarActivity { 

    final Context context = this; 
    private static final int EDIT = 0, DELETE = 1; 

    DatabaseTaskHandler dbHandler; 
    DatabaseReminderHandler dbRemHandler; 
    ListView taskListView; 
    ArrayAdapter<Task> taskAdapter; 

    int longClickedItemIndex; 

    List<Task> Tasks = new ArrayList<Task>(); 

    FragmentManager fm = getSupportFragmentManager(); 

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

     dbHandler = new DatabaseTaskHandler(this); 
     dbRemHandler = new DatabaseReminderHandler(this); 
     dbRemHandler.initReminders(getApplicationContext()); 
     taskListView = (ListView) findViewById(R.id.listViewTasks); 

     // The following piece of code allows to empty database before testing when reinstalling the app for test. 
     //getApplicationContext().deleteDatabase("myTasks"); 

     registerForContextMenu(taskListView); 

     taskListView.setOnLongClickListener(new View.OnLongClickListener() { 
      @Override 
      public boolean onLongClick(View v) { 
       return false; 
      } 
     }); 

     taskListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() { 
      @Override 
      public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) { 
       longClickedItemIndex = position; 
       return false; 
      } 
     }); 

     if (dbHandler.getTasksCount() != 0) 
      Tasks.addAll(dbHandler.getAllTasks()); 

     populateTasksList(); 
    } 


    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.menu_home_page, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 
/* 
     switch (id){ 
      case R.id.action_settings: 
       Intent intent = new Intent(this, RemindersSettings.class); 
       startActivity(intent); 
       break; 
      default: 
       return super.onOptionsItemSelected(item); 
     } 
*/ 
     //noinspection SimplifiableIfStatement 
     if (id == R.id.action_settings) { 
      return true; 
     } 

     return super.onOptionsItemSelected(item); 

     //return true; 
    } 

    private class TaskListAdapter extends ArrayAdapter<Task> { 

     public TaskListAdapter(){ 
      super(HomePage.this, R.layout.tasklist_item, Tasks); 
     } 

     @Override 
     public View getView(int position, View view, ViewGroup parent){ 
      if (view == null) { 
       view = getLayoutInflater().inflate(R.layout.tasklist_item, parent, false); 
      } 

      Task currentTask = Tasks.get(position); 

      TextView taskListName = (TextView) view.findViewById(R.id.txtTaskListName); 
      taskListName.setText(currentTask.getTitle()); 
      TextView taskListDate = (TextView) view.findViewById(R.id.txtTaskListDate); 
      taskListDate.setText(currentTask.getDate()); 
      TextView taskListTime = (TextView) view.findViewById(R.id.txtTaskListTime); 
      taskListTime.setText(currentTask.getTime()); 
      ImageButton deleteButton = (ImageButton) view.findViewById(R.id.btnDelete); 
      deleteButton.setTag(R.id.taskId,currentTask.getId()); 
      deleteButton.setTag(R.id.position,position); 
      Button editButton = (Button) view.findViewById(R.id.btnEdit); 
      editButton.setTag(R.id.taskId, currentTask.getId()); 
      editButton.setTag(R.id.position, position); 

      return view; 
     } 
    }

謝謝提前。 Alex。

來源

2015-03-02 Alexandre

我終於想出瞭如何解決它。

我到處都缺少不同db.open我設置他們中的一些，例如在我的主頁：

我設置：

dbHandler = new DatabaseTaskHandler(this); 
dbRemHandler = new DatabaseReminderHandler(this);

我也有加：

try { 
    dbHandler.open(); 
} catch (SQLException e) { 
      e.printStackTrace(); 
} 
try { 
    dbRemHandler.open(); 
} catch (SQLException e) { 
    e.printStackTrace(); 
}

現在工作正常。

Alex。

來源

2015-03-03 10:36:42 Alexandre

@Alexendre我爲您提供解決方案，在您發佈相同的解決方案後。這很奇怪！ – LaurentY 2015-03-04 15:50:06

不好意思，但是有一點與我的稍有不同，就像所說的，我必須添加try catch方法，沒有它我有問題。 – Alexandre 2015-04-20 11:39:10

在您的MainActivity中，您忘記了在類DatabaseReminderHandler上調用open（）方法。

dbRemHandler = new DatabaseReminderHandler(this); 
dbRemHandler.initReminders(getApplicationContext()); 
dbRemHandler.open();

來源

2015-03-03 10:12:01 LaurentY

設置2 SQLOpenHelper拋出錯誤表

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