android - 为什么我从 Android 数据库中的选择查询中得到 Null ArrayList？

Question

你好，我从这段代码中得到空数组列表：

public List<IndiviualUser> findBloodByBloodGroup(String final_blood_group)
    {
        List<IndiviualUser> userlist = new ArrayList<>();
        SQLiteDatabase db = getReadableDatabase();
    String select = "SELECT * FROM " + TABLE_NAME + " WHERE " + COL_4 + " = ' "+ final_blood_group + " ' " ;

    Cursor cursor = db.rawQuery(select,null);

    Log.d("FIND", "findBloodByBloodGroup"+ select);

    if(cursor.moveToFirst())
    {
        do
        {
            IndiviualUser user = new IndiviualUser();
            user.setName(cursor.getString(1));
            user.setPassword(cursor.getString(2));
            user.setBlood_Group(cursor.getString(3));
            user.setBlood_Quantity(cursor.getString(4));
            user.setMobile_No(cursor.getString(5));
            user.setLat2(cursor.getDouble(6));
            user.setLong2(cursor.getDouble(7));
            userlist.add(user);
        }
        while (cursor.moveToNext());
    }
    Log.d("SELECT","THE MSG WAS SELECTED SUCCESSFULLY " + userlist);
    return userlist;
}

我将在另一个活动中收到此用户列表代码如下：

 DataBaseHelper DBHepler;
    String str1,s1,s2,s5;
    double s3,s4;

DBHepler = new DataBaseHelper(Find_Blood_Now_Result.this);

List<IndiviualUser> indiviualUsers = DBHepler.findBloodByBloodGroup(str1);
        for(IndiviualUser user: indiviualUsers)
        {
            s1 = user.getName();
            s2 =  user.getMobile_No();
            s3 = user.getLat2();
            s4 = user.getLong2();
            s5 = user.getBlood_Group();
        }

当我设置所有字符串的文本时，它会给我空值，我希望你有解决方案谢谢。

标签： androidandroid-database