C# : textbox validation in windows forms using Keypress Event

private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
 {
 if(e.KeyCode == Keys.Enter)
   {
      if(String.IsNullOrEmpty(textBox1.Text))
         {
            MessageBox("Textbox cannot be empty","Title", MessageBoxButtons.OK, MessageBoxIcon.Error);
            textBox1.Focus();
         }
    else
        {
             //do something
        }  
   }                      
 }
}