C#

private void textBox2_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode.ToString() == "Return")
            {
               // required statement;
            }
        }

private void Form1_KeyUp(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.Enter)
    {
        Console.WriteLine("enter key seen");
    }
}

private void button1_Click(object sender, EventArgs e)
{
    Console.WriteLine("button click ... active Control is {0}", ActiveControl.Name);

    // submit code goes here
}

private void TextBoxes_KeyUp(object sender, KeyEventArgs e)
{
    if (! (e.KeyCode == Keys.Enter)) return;

    // disable submit ?
    button1.Enabled = false;

    TextBox activeTextBox = sender as TextBox;

    string currentText = activeTextBox.Text;
    
    // perform Validation here for conditions which must be true
    // for all TextBoxes that use this EventHandler

    // no TextBox can have more than 3 digits
    if(currentText.Where(ch => Char.IsDigit(ch)).ToList().Count > 3)
    {
        // for testing only
        Console.WriteLine("fail: TextBox{0} has more than 3 digits", activeTextBox);
        
        activeTextBox.Focus();
        e.Handled = true;
        return;
    }

    // perform Validation here that is unique to each TextBox

    switch (activeTextBox.Name)
    {
        case "textBox1":
            // example of unique validation
            // textBox1 must have at least 4 alpha-characters
            if (! (currentText.Where(ch => Char.IsLetter(ch)).ToList().Count == 4))
            {
                // for testing only
                Console.WriteLine("fail: TextBox1 does not have 4 letters");
                
                activeTextBox.Focus();
                e.Handled = true;
                return;
            }
            break;
        case "textBox2":
            break;
        case "textBox3":
            break;
    }

    // okay ... submit
    button1.Enabled = true;
    button1.PerformClick();
}

Control found = null;
foreach (Control c in Controls)
   {
   if (c is ucOptionsBarcode)
      {
      found = c;
      break;
      }
   }
if (found == null)
   {
   // Add it
   }
else
   {
   found.BringToFront();
   }

bool Control found = null;