无法从sqlite数据库检索数据

Question

在这个应用程序，我希望当我点击按钮从数据库中显示的数据在列表视图和通过使用OnItemClick（）它应该显示另一个活动但不幸的是我的应用程序正在被停止为我点击按钮Plzz告诉我其中m我得到错误这里是我的活动类`

public class DictionaryActivity extends Activity { 
protected EditText searchText; 
protected DatabaseHelper d; 
protected Cursor cursor; 
protected ListAdapter adapter; 
    protected ListView wordList; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 

    d = new DatabaseHelper(this); 

    d.addWord(new Contact("Apple", "Fruit")); 
    d.addWord(new Contact("Ape", "Animal")); 
    d.addWord(new Contact("Boy", "Male")); 
    d.addWord(new Contact("Bat", "Playing Object")); 

    searchText = (EditText) findViewById(R.id.word); 
    wordList = (ListView) findViewById(R.id.list); 

    final Button button = (Button) findViewById(R.id.search); 
    button.setOnClickListener(new View.OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      // TODO Auto-generated method stub 

      searchword(v); 
     } 
    }); 

} 

public void searchword(View view) { 

    // || is the concatenation operation in SQLite 
    cursor = d.getData(searchText); 
    adapter = new SimpleCursorAdapter(this, R.layout.word_list, cursor, 
      new String[] { "word" }, new int[] { R.id.word }); 
    wordList.setAdapter(adapter); 

    wordList.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> parent, View view, 
       int position, long id) { 
      // TODO Auto-generated method stub 
      Intent intent = new Intent(getApplicationContext(), 
        WordDetails.class); 
      Cursor cursor = (Cursor) adapter.getItem(position); 
      intent.putExtra("Word_ID", 
        cursor.getInt(cursor.getColumnIndex("id"))); 
      startActivity(intent); 
     } 

    }); 
}}` 

下面是DataBaseHelper类

public class DatabaseHelper extends SQLiteOpenHelper { 
protected SQLiteDatabase db; 
private static final int DATABASE_VERSION = 1; 

// Database Name 
private static final String DATABASE_NAME = "Word_Meanings"; 

// Contacts table name 
private static final String TABLE_NAME = "Meanings"; 

// Contacts Table Columns names 
private static final String KEY_ID = "id"; 
private static final String KEY_WORD = "word"; 
private static final String KEY_MEAN = "mean"; 

private Contact contact; 

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

// Creating Tables 
@Override 
public void onCreate(SQLiteDatabase db) { 
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_NAME + "(" 
      + KEY_ID + " INTEGER PRIMARY KEY," + KEY_WORD + " TEXT," 
      + KEY_MEAN + " TEXT" + ")"; 
    db.execSQL(CREATE_CONTACTS_TABLE); 
} 

// Upgrading database 
@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    // Drop older table if existed 
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME); 

    // Create tables again 
    onCreate(db); 
} 

// Adding new contact 
void addWord(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_WORD, contact.getword()); // Contact Name 
    values.put(KEY_MEAN, contact.getmean()); // Contact Phone 

    // Inserting Row 
    db.insert(TABLE_NAME, null, values); 
    db.close(); // Closing database connection 
} 

// Updating single contact 
public int updateWord(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_WORD, contact.getword()); 
    values.put(KEY_MEAN, contact.getmean()); 

    // updating row 
    return db.update(TABLE_NAME, values, KEY_ID + " = ?", 
      new String[] { String.valueOf(contact.getID()) }); 
} 

// Deleting single contact 
public void deleteWord(Contact contact) { 
    this.contact = contact; 
    SQLiteDatabase db = this.getWritableDatabase(); 
    db.delete(TABLE_NAME, KEY_ID + " = ?", 
      new String[] { String.valueOf(contact.getID()) }); 
    db.close(); 
} 

// Getting contacts Count 
public int getCount() { 
    String countQuery = "SELECT * FROM " + TABLE_NAME; 
    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(countQuery, null); 
    cursor.close(); 

    // return count 
    return cursor.getCount(); 
} 

public Cursor getData(EditText s) { 
    // TODO Auto-generated method stub 


    String sql = "SELECT id, word FROM Meanings WHERE word LIKE ?"; 


    String sqlArgs[] = new String[] { s.getText().toString() + "%" }; 


    Cursor c = db.rawQuery(sql, sqlArgs); 


    return c; 

}} 

这里是logcat的：

E/AndroidRuntime(543): FATAL EXCEPTION: main E/AndroidRuntime(543): java.lang.NullPointerException 
E/AndroidRuntime(543): at com.Dictionary.DatabaseHelper.getData(DatabaseHelper.java:107) 
E/AndroidRuntime(543): at com.Dictionary.DictionaryActivity.searchword(DictionaryActivity.java:56) 
E/AndroidRuntime(543): at com.Dictionary.DictionaryActivity$1.onClick(DictionaryActivity.java:47) 
E/AndroidRuntime(543): at android.view.View.performClick(View.java:3511) 
E/AndroidRuntime(543): at android.view.View$PerformClick.run(View.java:14105) 
E/AndroidRuntime(543): at android.os.Handler.handleCallback(Handler.java:605) 
E/AndroidRuntime(543): at android.os.Handler.dispatchMessage(Handler.java:92) 
E/AndroidRuntime(543): at android.os.Looper.loop(Looper.java:137) 
E/AndroidRuntime(543): at android.app.ActivityThread.main(ActivityThread.java:4424) 
E/AndroidRuntime(543): at java.lang.reflect.Method.invokeNative(Native Method) 
E/AndroidRuntime(543): at java.lang.reflect.Method.invoke(Method.java:511) 
E/AndroidRuntime(543): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
E/AndroidRuntime(543): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) E/AndroidRuntime(543): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

当使用Cursor来填充Adapter，所述Cursor必须包含一个称为_id列（注意前述_字符）。

要么改变你的数据库CREATE使用_id代替id或改变SELECT别名id到_id。例如...

String sql = "SELECT id as _id, word FROM Meanings WHERE word LIKE ?"; 

注意：如果你需要做的事情一样SELECT * ...你将不能够明显别名id列。在这种情况下，通常最好使用_id列创建数据库表。

编辑：顺便说一句，您的getCount()方法将失败，因为您在尝试使用return cursor.getCount()之前调用cursor.close()。当您关闭Cursor时，其资源将被释放，并且Cursor将失效，这意味着cursor.getCount()将不起作用。

编辑：另外，如上所述，在getData(...)方法中调用db.rawQuery(...)之前，请使用SQLiteDatabase db = getReadableDatabase()。