c# - Mono.Data.Sqlite.SqliteException：尝试返回阅读器时

Question

我正在尝试返回一个阅读器，以便我可以在另一堂课中阅读它。当我调用它时： return cmd.ExecuteReader(); 我得到一个 Mono.Data.Sqlite.SqliteException: 当我尝试调用插入查询并调用 cmd.ExecuteNonQuery(); 时也会发生同样的事情。我有以下课程：

数据库.cs：

public class Database
    {
    private SqliteConnection connection;
    public string connectiondata;
    private static string _LocalDatabasePath = Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal), "LocalData.db3");

    public Database(string ConnectionString)
    {
        this.connection = new SqliteConnection(ConnectionString);
    }

    public Database(SqliteConnection Connection)
    {
        this.connection = Connection;
    }

    public static UsersDatabase User { get { return new UsersDatabase("Data Source=" + _LocalDatabasePath); } }

    #region Queries

    protected SqliteDataReader SelectQuery(string columns, string table, string condition)
    {
        if (this.Connected)
        {
            SqliteCommand cmd = this.connection.CreateCommand();
            cmd.CommandText = "SELECT " + columns + " FROM " + table + (string.IsNullOrEmpty(condition) ? "" : " WHERE " + condition);
            cmd.CommandType = CommandType.Text;
            return cmd.ExecuteReader();
        }
        else
        {
            throw new Exception("Inte ansluten till databasen");
        }
    }

    protected SqliteDataReader SelectQuery(string columns, string table)
    {
        return this.SelectQuery(columns, table, "");
    }
    protected void InsertQuery(string table, string columns, string values)
    {
        if (this.Connected)
        {
            SqliteCommand cmd = this.connection.CreateCommand();
            cmd.CommandText = "INSERT INTO " + table + "(" + columns + ") VALUES(" + values + ")";
            cmd.ExecuteNonQuery();
        }
        else
        {
            throw new Exception("Inte ansluten till databasen");
        }
    }

    #endregion

    #region Connection
    public bool Connected
    {
        get
        {
            if (this.connection == null)
            {
                return false;
            }
            if (this.connection.State == ConnectionState.Open)
            {
                return true;
            }
            return false;
        }
    }
    public void Connect()
    {
        if (!this.Connected)
        {
            string db = _LocalDatabasePath;
            bool exists = File.Exists(db);
            if (!exists)
            {
                SqliteConnection.CreateFile(db);
            }
            this.connection = new SqliteConnection("Data Source=" + db);
            this.connection.Open();
        }
    }
    public void Close()
    {
        if (this.Connected)
        {
            this.connection.Close();
        }
    }
    #endregion
}

}

用户数据库.cs：

public class UsersDatabase : Database
    {
public UsersDatabase(string connectionstring)
            : base(connectionstring)
        {
        }
        public UsersDatabase(SqliteConnection connection)
            : base(connection)
        {
    }

    public void CreateUser()
    {
        this.Connect();
        this.InsertQuery("People", "PersonID, FirstName, LastName", "'" + "namn11" + "', '" + "enamn11" + "'");
        this.Close();

    }

    public UserStruct[] GetAllUsers()
    {
        List<UserStruct> templist = new List<UserStruct>();

        this.Connect();
        SqliteDataReader reader = this.SelectQuery("*", "People", "");
        while (reader.Read())
        {
            UserStruct tmpuser = new UserStruct();
            tmpuser.ID = reader["PersonID"].ToString();
            tmpuser.Name = reader["FirstName"].ToString();
            tmpuser.LastName = reader["LastName"].ToString();
            templist.Add(tmpuser);
        }
        this.Close();

        return templist.ToArray();
    }
}

活动1.cs：

[Activity(Label = "example_proj", MainLauncher = true, Icon = "@drawable/icon")]
    public class Activity1 : Activity
    {

        protected override void OnCreate(Bundle bundle)
        {
            base.OnCreate(bundle);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            Button btn2 = FindViewById<Button>(Resource.Id.btn2);
            btn2.Click += new EventHandler(btn2_Click);

        }

        void btn2_Click(object sender, EventArgs e)
        {
            UserStruct[] tmpusr = UsersDatabase.User.GetAllUsers();//get usrs
        }

    }

所以...从活动中，我调用 UsersDatabase GetAllUsers() 或 CreateUser()。UsersDatabase 使用 Database 类来帮助查询和连接。因此，从 UsersDatabase 我首先调用 Connect() 方法来建立与 DB 的连接，然后我调用例如 SelectQuery() 来返回一个读取器，我稍后将在 UsersDatabase 类中读取该读取器并用正在执行的信息填充一个结构要返回到活动1。

正如我所说，当我遇到异常时，我会尽可能地返回读者。连接打开并且数据库存在。