How to disable the parent form when a child form is active?

Question

Have you tried using Form.ShowDialog() instead of Form.Show()?

ShowDialog shows your window as modal, which means you cannot interact with the parent form until it closes.

Are you calling ShowDialog() or just Show() on your child form from the parent form?

ShowDialog will "block" the user from interacting with the form which is passed as a parameter to ShowDialog.

Within the parent you might call something like:

MyChildForm childForm = new MyChildForm();

childForm.ShowDialog(this);

where this is the parent form.

Its simple, use

Form.ShowDialog();

Instead of

Form.Show();

While using Form.ShowDialog(), you cannot interact with the parent form until it closes.

What you could do, is to make sure to pass the parent form as the owner when showing the child form:

  Form newForm = new ChildForm();
  newForm.Show(this);

Then, in the child form, set up event handlers for the Activated and Deactivate events:

private void Form_Activated(object sender, System.EventArgs e)
{
    if (this.Owner != null)
    {
        this.Owner.Enabled = false; 
    }
}

private void Form_Deactivate(object sender, System.EventArgs e)
{
    if (this.Owner != null)
    {
        this.Owner.Enabled = true;
    }
}

However, this will result in a truly wierd behaviour; while you will not be able to go back and interact with the parent form immediately, activating any other application will enable it, and then the user can interact with it.

If you want to make the child form modal, use ShowDialog instead:

  Form newForm = new ChildForm();
  newForm.ShowDialog(this);