未将对象引用实例化问题

Question

    protected void btn_tijiao_Click(object sender, EventArgs e)
    {
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+Server.MapPath("mytest.mdb");
        conn.Open();
        //OleDbCommand cmd=new OleDbCommand();
        OleDbCommand cmd=conn.CreateCommand();
        string sql = "insert into userinfo(username,password,province,sex,intro,register_time) values(" +
            "'" + tb_username.Text + "'" + "," +
            "'" + tb_password.Text + "'" + "," +
            "'" + ddl_province.SelectedItem.Text + "'" + "," +
            "'" + rbl_sex.SelectedItem.Text + "'" + "," +
            "'" + tb_info.Text + "'" + "," +
            "#" + DateTime.Now + "#)";        cmd.CommandText=sql;
        int i=cmd.ExecuteNonQuery();
        conn.Close();
        lb_message.Text="已经成功添加，请自己打开数据库mytest.mdb 查看结果";    }问题错误在SQL语句显示

Answer 1

string connectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+Server.MapPath("mytest.mdb"); 
OleDbConnection conn = new OleDbConnection(connectionString);

Answer 2

注意Insert语句。protected void btn_tijiao__Click(object sender, EventArgs e)
{
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + Server.MapPath("App_Data/db1.mdb");        OleDbCommand cmd = conn.CreateCommand();
        cmd.CommandText = "insert into userinfo values(@username,@password,@province,@sex,@info,@register_time)";
        cmd.Parameters.AddWithValue("username", tb_username.Text);
        cmd.Parameters.AddWithValue("password", tb_password.Text);
        cmd.Parameters.AddWithValue("province", ddl_province.SelectedItem.Text);
        cmd.Parameters.AddWithValue("sex", rbl_sex.SelectedItem.Text);
        cmd.Parameters.AddWithValue("info", tb_info.Text);
        cmd.Parameters.AddWithValue("register_time", DateTime.Now.ToString());
        
        conn.Open();
        int i = cmd.ExecuteNonQuery();
        conn.Close();
        lb_message.Text = "已经成功添加，请自己打开数据库mytest.mdb 查看结果"; }

Answer 3

insert into userinfo values(@username,@password,@province,@sex,@info,@register_time)
??? 脑子被门夹了

Answer 4

please shut up. 没试过之前请闭嘴。