Select one record in GridView (Form1) and it show display in Text Box(Form2)

Ok I'm going to walk you through a possible (note - possible and not necessarily the best) solution because I don't like the one that has already been posted.

A couple of things you have to consider ... what is displaying the second form and how do you keep a note of it's instance.

I've created a simple WinForm application that has two forms - Form1 and Form2.

Form1 has a DataGridView (dataGridView1) which for the purposes of this has a single column populated with numbers 0 to 99.

Form2 has a single TextBox (textBox2)

I'm using the SelectionChanged event on the DataGridView to handle the display in the second form.

Here's my code - I've tried to add appropriate comments to explain my thinking.

using System;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        // Declare the second form at the class level of Form1
        private Form2 f2 = new Form2();

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // DEMO ONLY
            // Put some data into the datagridview
            for (int i = 0; i < 100; i++)
                dataGridView1.Rows.Add(i.ToString());
        }

        private void dataGridView1_SelectionChanged(object sender, EventArgs e)
        {
            if (f2.Visible == false)
                f2.Show();  // make sure form2 is visible

            // Find the textbox on form2
            TextBox t = (TextBox)f2.Controls.Find("textBox2", true)[0];

            // Populate the textbox with some data from the grid
            t.Text = dataGridView1.SelectedCells[0].Value.ToString();

        }
    }
}

If you want to research other ways (and you should) try starting here with this code project article[^]