Style- DataTrigger例子(Text长度)

Text长度小于7时，边框变为红色

    <Window.Resources>
        <local:L2BConverter x:Key="cvtr"/>
        <Style TargetType="TextBox">
            <Style.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={x:Static RelativeSource.Self},
                                               Path=Text.Length,
                                               Converter={StaticResource cvtr}}"
                             Value="false">
                    <Setter Property="BorderBrush" Value="Red"/>
                    <Setter Property="BorderThickness" Value="1"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>

    <StackPanel>
        <TextBox Margin="5"/>
        <TextBox Margin="5,0"/>
        <TextBox Margin="5"/>
    </StackPanel>

    public class L2BConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            int textLength = (int)value;
            return textLength >  ? true : false;

        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }