Windows Forms: How to fill ComboBox and DataGridView automatically in C#

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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