Android:SQLite，cursor.moveToNext() 总是返回 false

Question

以下语句 cursor.moveToNext() 始终为 false。我希望循环执行一次。我测试过查询实际上返回了数据。

谁知道这是怎么回事？

    String query ="SELECT(SELECT COUNT(*) FROM Table1) as count1, (SELECT COUNT(*) FROM Table2) as count2;";

    Cursor mCursor = mDb.rawQuery(query, null);

    if (mCursor != null) {
        mCursor.moveToFirst();
    }

    while (cursor.moveToNext()) {   //<---------------return false here???
        String result_0=cursor.getString(0);
    }

Answer 1

我知道您已经解决了您的问题，但这里是对发生的事情的演练:

Cursor mCursor = mDb.rawQuery(query, null);

// At this point mCursor is positioned at just before the first record.

if (mCursor != null) {
    mCursor.moveToFirst();
    // mCursor is now pointing at the first (and only) record
}

while (mCursor.moveToNext()) {
    String result_0=cursor.getString(0);
}

// The loop above was skipped because `.moveToNext()` caused mCursor
// to move past the last record.

因此，在您只需要一条记录的情况下，您只需要mCursor.moveToFirst() 或您的mCursor.moveToNext().