SL4.DataAnnotations 데이터 검증 방법

    <Grid x:Name="LayoutRoot" Background="White"  BindingValidationError="LayoutRoot_BindingValidationError">
        <StackPanel>
            <Button Name="MyButton" Content="Update"  Click="MyButton_Click"  Width="65" Height="41"></Button>
            <TextBlock Text="  ：" Name="tbAccount"  Width="50"></TextBlock>
            <TextBox Width="150" Name="TxtUserName"  Text="{Binding Path=UserName, Mode=TwoWay, ValidatesOnExceptions=True, NotifyOnValidationError=True}"></TextBox>
            
        </StackPanel>
    </Grid>

        private void LayoutRoot_BindingValidationError(object sender, ValidationErrorEventArgs e)
        {
            if (e.Action == ValidationErrorEventAction.Added)
                (e.OriginalSource as Control).Background = new SolidColorBrush(Colors.Yellow);

            if (e.Action == ValidationErrorEventAction.Removed)
                (e.OriginalSource as Control).Background = new SolidColorBrush(Colors.White);
        }

        Users u = new Users();
        public MainPage()
        {
            InitializeComponent();
            TxtUserName.DataContext = u;
        }

        private string _UserName="";
        [Required(ErrorMessage="      ")]
        [StringLength(20,ErrorMessage="       20   ")]
        public string UserName
        {
            get
            {
                return _UserName;
            }
            set
            {
                if(_UserName != value)
                     Validator.ValidateProperty(value,new ValidationContext(this,null,null){MemberName="UserName"});
                _UserName=value;
            }
        }