从数据库错误检索C＃数据

Question

i have tried to to load the data to text box, while selecting the drop down list, i was created a class for retrieval and called it in drop down list selected index changed. But i cant get the answer what i want. If i have called the class in Button click event it has worked properly. So please correct me. What i made a mistake. This is what my code:

public void so()
    {
        con.Open();
        string s2;
        s2 = "select Source from tbl_component where Componetcode='" + Mcodeddl.SelectedItem.Text + "'";
        SqlCommand c2 = new SqlCommand(s2, con);
        SqlDataReader d2;
        d2 = c2.ExecuteReader();
        while (d2.Read())
        {
            TextBox1.Text = d2["Source"].ToString().Trim(); 

        }
        d2.Close();
        con.Close();
    }

//i have called the so class here

 protected void Mcodeddl_SelectedIndexChanged(object sender, EventArgs e)
    {
        so();   
    }

Answer 1

您应该在Mcodeddl_SelectedIndexChanged方法内设置一个断点，以查看是否触发了该事件，并确保在下拉列表定义中包含AutoPostBack="true"

Answer 2

Make sure you have specified OnSelectedIndexChanged event for the drop down in aspx page

<asp:DropDownList ID="Mcodeddl" runat="server" 
    OnSelectedIndexChanged= "Mcodeddl_SelectedIndexChanged">
</asp:DropDownList>

Also use parameterized SQL queries.

PS. Your SO(); is a method not a class.

Answer 3

i have got the answer. And i gave the detail what exactly i have did. "Set AutoPostBack=True"