Step 1: Click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "LinkCombobox" and then click OK
Step 2: Design your form as below

Step 3: Create an EF Model, then add a category table form northwind database to your Entity Framework Model

Step 4: Add code to handle your form as below
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace LinkCombobox
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
try
{
//Load category data
using (NorthwindEntities db = new NorthwindEntities())
{
cboCategory.DataSource = db.Categories.ToList();
cboCategory.ValueMember = "CategoryID";
cboCategory.DisplayMember = "CategoryName";
}
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
private void cboCategory_SelectionChangeCommitted(object sender, EventArgs e)
{
Cursor.Current = Cursors.WaitCursor;
//Update data to textbox
Category obj = cboCategory.SelectedItem as Category;
if (obj != null)
{
txtCategoryID.Text = obj.CategoryID.ToString();
txtCategoryName.Text = obj.CategoryName;
txtDescription.Text = obj.Description;
}
Cursor.Current = Cursors.Default;
}
}
}
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