Update record based on ComboBox value in UserControl in C# and VB.Net

Refer below sample.

Database

I have made use of the following table Customers with the schema as follows.

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

Form Design

User Control

Form

Namespaces

C#

using System.Configuration;
using System.Data.SqlClient;

VB.Net

Imports System.Configuration
Imports System.Data.SqlClient

Code

User Control

C#

private void btnFill_Click(object sender, EventArgs e)
{
    this.FillComboBox();
}

private void FillComboBox()
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    string sql = "SELECT CustomerId FROM Customers";
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(sql, con))
        {
            con.Open();
            using (SqlDataReader sdr = cmd.ExecuteReader())
            {
                while (sdr.Read())
                {
                    cbCustomers.Items.Add(sdr["CustomerId"]);
                }
                cbCustomers.SelectedIndex = 0;
            }
            con.Close();
        }
    }
}

VB.Net

Private Sub btnFill_Click(sender As Object, e As EventArgs) Handles btnFill.Click
    Me.FillComboBox()
End Sub

Private Sub FillComboBox()
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Dim sql As String = "SELECT CustomerId FROM Customers"
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand(sql, con)
            con.Open()
            Using sdr As SqlDataReader = cmd.ExecuteReader()
                While sdr.Read()
                    cbCustomers.Items.Add(sdr("CustomerId"))
                End While
                cbCustomers.SelectedIndex = 0
            End Using
            con.Close()
        End Using
    End Using
End Sub

Form

C#

private void btnUpdate_Click(object sender, EventArgs e)
{
    string selectedId = (ucCustomers.Controls.Find("cbCustomers", true)[0] as ComboBox).SelectedItem.ToString();
    string query = "UPDATE Customers SET Name=@Name WHERE CustomerId=@CustomerId";
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            cmd.Parameters.AddWithValue("@CustomerId", selectedId);
            cmd.Parameters.AddWithValue("@Name", txtName.Text);
            cmd.Connection = con;
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
}

VB.Net

Private Sub btnUpdate_Click(sender As Object, e As EventArgs) Handles btnUpdate.Click
    Dim selectedId As String = (TryCast(ucCustomers.Controls.Find("cbCustomers", True)(0), ComboBox)).SelectedItem.ToString()
    Dim query As String = "UPDATE Customers SET Name=@Name WHERE CustomerId=@CustomerId"
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Using cmd As SqlCommand = New SqlCommand(query)
            cmd.Parameters.AddWithValue("@CustomerId", selectedId)
            cmd.Parameters.AddWithValue("@Name", txtName.Text)
            cmd.Connection = con
            con.Open()
            cmd.ExecuteNonQuery()
            con.Close()
        End Using
    End Using
End Sub