private void btnOk_Click(object sender, EventArgs e) { // If there's a validation function, check and only set if valid, otherwise assume all text is valid. if (EntryValidation != null) { if (!EntryValidation.Invoke(tbInput.Text)) // Validation fails. { MessageBox.Show("Invalid Entry!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); return; } } Hide(); }