什么是queryBuilder.appendWhere()的作用？在安卓中。

Question

在这里使用 queryBuilder.appendWhere() 有什么意义呢? 在 Cursor cursor = queryBuilder.query() 中设置 where 子句不是更简单吗？或者说，这两种设置“where”子句的方式是不同的吗？

  public Cursor query(Uri uri, String[] projection, String selection,
      String[] selectionArgs, String sortOrder) {

    // Uisng SQLiteQueryBuilder instead of query() method
    SQLiteQueryBuilder queryBuilder = new SQLiteQueryBuilder();

    // Check if the caller has requested a column which does not exists
    checkColumns(projection);

    // Set the table
    queryBuilder.setTables(TodoTable.TABLE_TODO);

    int uriType = sURIMatcher.match(uri);
    switch (uriType) {
    case TODOS:
      break;
    case TODO_ID:
      // Adding the ID to the original query
      queryBuilder.appendWhere(TodoTable.COLUMN_ID + "="
          + uri.getLastPathSegment());
      break;
    default:
      throw new IllegalArgumentException("Unknown URI: " + uri);
    }

    SQLiteDatabase db = database.getWritableDatabase();
    Cursor cursor = queryBuilder.query(db, projection, selection,
        selectionArgs, null, null, sortOrder);
    // Make sure that potential listeners are getting notified
    cursor.setNotificationUri(getContext().getContentResolver(), uri);

    return cursor;
  }

- Blake

Answer 1

如果你是基于条件建立where语句的，你可以使用appendWhere()。

- CommonsWare