Question

我正在尝试从名称与提供的字符串匹配的距离列中获取值。参见下面的代码：

    public String getDistance(String station_name){
    String distance = null;
    Cursor cursor = database.rawQuery("SELECT distance from station_data where name =? ", new String[] {station_name} );
    cursor.moveToFirst();
    while(cursor.moveToNext()){
        distance = cursor.getString(0);
        cursor.moveToNext();
    }
    cursor.close();
    return distance;
}

我在android的Assets文件夹中使用了一个外部数据库文件，并使用了几乎相同的功能来填充我的微调框。它与微调器一起正常工作，但使用上述函数时返回空值。这是我的桌子：

帮我找出问题所在。预先感谢。

Answer 1

    //Once try this. It will definitely work.


public String getDistance(String station_name){
            String distance = null;
            Cursor cursor = database.rawQuery("SELECT distance from station_data where name =? ", new String[] {station_name} );

            if (cursor.moveToFirst())
            {
                distance = cursor.getString(0);
            }      

            cursor.close();

            return distance;
        }

//有关代码中的错误，请参见此处。

// cursor.moveToFirst（）将光标移动到光标的第一个索引。

// cursor.moveToNext（）将光标移至下一个索引。

//看您在这里做什么。

public String getDistance(String station_name){
        String distance = null;
        Cursor cursor = database.rawQuery("SELECT distance from station_data where name =? ", new String[] {station_name} );
        cursor.moveToFirst();  // CURSOR INDEX = 0
        while(cursor.moveToNext()){ // CURSOR INDEX = 1
            distance = cursor.getString(0);
            cursor.moveToNext();
        }
        cursor.close();
        return distance;
    }

Answer 2

我执行的迭代有问题工作代码如下：

    public String getDistance(String station_name){
    String distance = null;
    Cursor cursor = database.rawQuery("SELECT distance from station_data WHERE name =? ", new String[] {station_name} );
    cursor.moveToFirst();
    while(!cursor.isAfterLast()){
        distance = cursor.getString(0);
        cursor.moveToNext();
    }
    cursor.close();
    return distance;
}

Answer 3

public String getDistance(String station_name){
String distance = null;
Cursor cursor = database.rawQuery("SELECT distance from station_data where name =? ", 
new String[] {station_name} );
if(cursor.length() > 0){
    cursor.moveToFirst();
    distance = cursor.getString(0);          
}
cursor.close();      
return distance;

使用Android在SQLite数据库表中使用WHERE子句检索值

3 个答案: