Problem leaving form as top c#

Question

I have 2 Forms. The main contains a button that opens the second form inside the main.

private void btnCalculadora_Click(object sender, EventArgs e)
    {
        Calculadora = new frmCalculadora();
        Calculadora.TopLevel = false;
        Calculadora.Visible = true;
        this.Controls.Add(this.Calculadora);
        Calculadora.Location = new Point(210, 40);
    }

But I would like that when the high school was opened, he would be selected, so that the event Keypress of the secondary form functioned, but Calculator.Toplevel = false; does not allow.

Note: Leaving Toplevel = true / this.Controls.Add(this.Calculator); of error.

Answer 1

Put your Main Form as MdiContainer, and define the MdiParent from your secondary form, as your main form.

Example:

private void btnCalculadora_Click(object sender, EventArgs e)
{
    Calculadora = new frmCalculadora();
    Calculadora.MdiParent = this;
    Calculadora.Location = new Point(210, 40);
    Calculadora.Show();
}

The Mdicontainer property can be set in the Main Form by the visual studio interface in the Form properties window