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

Step 3: Create an Entity Framework Model, then select Category and Product table from Northwind database

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 DataGridViewAndCombobox
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
try {
//Init data
using (NorthwindEntities db = new NorthwindEntities())
{
db.Configuration.ProxyCreationEnabled = false;
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)
{
Category obj = cboCategory.SelectedItem as Category;
if(obj != null)
{
Cursor.Current = Cursors.WaitCursor;
try {
using (NorthwindEntities db = new NorthwindEntities())
{
//Using linq to query data
db.Configuration.ProxyCreationEnabled = false;
var query = from o in db.Products
where o.CategoryID == obj.CategoryID
select o;
dataGridView.DataSource = query.ToList();
}
}
catch(Exception ex)
{
MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
Cursor.Current = Cursors.Default;
}
}
}
}
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