private void vendasBtn1_Click(object sender, EventArgs e)
{
if (telaVenda == null)
{
telaVenda = new TelaVenda();
telaVenda.Disposed += new EventHandler(telaVenda_Disposed);
telaVenda.Show();
}
}
void telaVenda_Disposed(object sender, EventArgs e)
{
telaVenda = null;
}