Question

说我有这样的帮手：

public class SqlHelper extends SQLiteOpenHelper {

    public SqlHelper(Context context, String name, CursorFactory factory, int version) {
        super(context, name, factory, version);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        db.execSQL("CREATE TABLE MyTable (ID INTEGER PRIMARY KEY, NAME TEXT, PLACE TEXT)");
        db.execSQL("INSERT INTO MyTable (NAME, PLACE) VALUES('ANTHONY','USA')");
        db.execSQL("INSERT INTO MyTable (NAME, PLACE) VALUES('BERIMOR','UK')");
        db.execSQL("INSERT INTO MyTable (NAME, PLACE) VALUES('IVAN','RUSSIA')");
    }


    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
    }


}

在我的主代码中执行查询

    SqlHelper sqlHelper = new SqlHelper(this, "MyDataBase.db", null, 1);
    SQLiteDatabase DB = sqlHelper.getReadableDatabase();

    Cursor c = DB.query(
            "MyTable" /* table */,
            new String[] { "PLACE" } /* columns */,
            "id = ?" /* where or selection */,
            new String[] { "RUSSIA" } /* selectionArgs */,
            null /* groupBy */,
            null /* having */,
            null /* orderBy */
        );

    DB.close();

但我不确定那个光标是什么？它不应该像数组吗？如果是这样，我如何从中获取原始值（字符串）？像这样的查询应该返回'IVAN'。

谢谢！

EDIT2：

这个（c.getCount（））仍然返回0，即没有结果...嗯......也许那里有帮手的东西？

     Cursor c = DB.query(
                "MyTable" /* table */,
                new String[] { "NAME" } /* columns */,
                "PLACE = 'RUSSIA'" /* where or selection */,
                null /* selectionArgs */,
                null /* groupBy */,
                null /* having */,
                null /* orderBy */
            );



    Log.e("DB RETURNS", String.valueOf( c.getCount() ) );

Answer 1

游标是指向查询结果集的指针。阅读Cursor文档： http://developer.android.com/reference/android/database/Cursor.html

基本上，你会做类似的事情：

String place;
if (c.moveToFirst){
    place = c.getString( c.getColumnIndex("PLACE"));
}

Answer 2

查询返回的Cursor对象提供对记录集的访问结果。

获得Cursor后，必须遍历它以获取值。在你的情况下，你会这样做 -

if (cur.moveToFirst()) {
    int placeColumn = cur.getColumnIndex("PLACE"); 
    String place = cur.getString(placeColumn);
}

要根据PLACE的查询取出NAME，您应该PLACE = ?

 Cursor c = DB.query(
            "MyTable" /* table */,
            new String[] { "NAME" } /* columns */,
            "PLACE = ?" /* where or selection */,
            new String[] { "RUSSIA" } /* selectionArgs */,
            null /* groupBy */,
            null /* having */,
            null /* orderBy */
        );

Android SQLite，如何将Cursor转换为字符串？

2 个答案: