private void TextBoxPassword_TextChanged(object sender, System.Windows.Controls.TextChangedEventArgs e)
{
String str = TextBoxPassword.Text.Trim();
if (str.Length > 18)
{
TextBoxPassword.Text = str.Remove(18);
MessageBox.Show("用户名长度不能超过18个字符!", "操作提示");
TextBoxPassword.Select(str.Length, 0);
}
}