Question

When I run my application 2 different forms are loaded simultaneously,but one of them is shown.Now I want If one of these form is closed ,other form which is hidden should get closed also.Any Suggestion.
No Parent -Child relation between these forms.

Answer 1

Assuming that the two forms are both in the same process, you can have the second hidden form handle the FormClosed event of the visible form and close it self when the Visible Form’s FormClosed event fires.

  public partial class Form1 : Form
  {
    private void Form1_Load(object sender, EventArgs e)
    {
      // The following does not need to happen in the Load of this form

      // Create hidden Form
      Form2 frm = new Form2();

      // Attach hidden form to this form
      frm.AttachTo(this);
    }
  }

  public class Form2 : Form
  {
    public void AttachTo(Form frmMain)
    {      
      frmMain.FormClosed += new FormClosedEventHandler(frmMain_FormClosed);
    }

    void  frmMain_FormClosed(object sender, FormClosedEventArgs e)
    {
      this.Close();
    }
  }