i want only new form opened...and close old form please help me

The new form was opened because you used code along the lines of:

ItemGroupForm igf = new ItemGroupForm();
...
igf.Show();

Which will always create a new instance.
Since you open the Grid form from the textbox form, why not pass the data back to the existing textbox form instead of creating a new one? It's not that complex, and it means your code is more OOP oriented and easier to maintain. Have a look at this: Transferring information between two forms, Part 2: Child to Parent[^]
And think of the Grid form as the Child, and the TextBox form as the Parent (Since it opened the Grid form in the first place).

this.hide() method


or


use constructor

when you come from form1 on form 2 take some integer value in constructor then write code form object.hide()

i hope, this code helps you

REGISTRATION reg = new REGISTRATION();
           bool onsiteopen = false;
           foreach (Form S in Application.OpenForms)
           {
               if (S is REGISTRATION)
               {
                   onsiteopen = true;
               }

           }
           if (onsiteopen == true)
           {
               MessageBox.Show("this form is already open.");
               reg.Activate();
           }
           else
           {
               reg.MdiParent = this;
               reg.Show();
           }

Simple do this on datagrid cell double click

Textbox1.Text = dataGridView1[0, e.RowIndex].Value.ToString();

see this

private void dataGridView1_CellDoubleClick(object sender, DataGridViewCellEventArgs e)
        {
            Textbox1.Text = dataGridView1[0, e.RowIndex].Value.ToString();
           
        }

0 is my ID Column so ill get id on text box

Anyone can give me proper code??? stil i cant found solution...