TextBox中只能输入数字并且首位不能为0

 e.Handled = true;
            if ((e.KeyChar >= '0' && e.KeyChar <= '9') || (e.KeyChar == (char)8))
            {
                if ((e.KeyChar == (char)8)) { e.Handled = false; return; }
                else
                {
                    int len = this.txtOrderAccount.Text.Trim().Length;

                    if (len == 0 && e.KeyChar != '0')
                    {
                        e.Handled = false; return;
                    }
                    else if (len == 0)
                    {
                        e.Handled = true;
                        return;
                    }
                    e.Handled = false; return;
                }
            }
            else
            {
                e.Handled = true;

            }