Apply style to Windows Phone TextBox when it doesn't contain text - silverlight

Question

I'm trying to find out a way to apply a style to a TextBox element when it does not contain text. I want the TextBox to have a different background color (for instance) when it does or does not contain any text.
As Triggers are not something that I can use in Silverlight (afaik), is there another way to do this? Preferrably without writing a custom implementation of TextBox just for this behavior. Thanks.
I ended up using a default behavior (ConditionBehavior):
<i:Interaction.Triggers>
<i:EventTrigger EventName="TextChanged">
<i:Interaction.Behaviors>
<ec:ConditionBehavior>
<ec:ConditionalExpression>
<ec:ComparisonCondition LeftOperand="{Binding Text, ElementName=textBox}" RightOperand="" Operator="NotEqual"/>
</ec:ConditionalExpression>
</ec:ConditionBehavior>
</i:Interaction.Behaviors>
<ec:ChangePropertyAction PropertyName="Background" Value="{StaticResource PhoneTextBoxBrush}" />
</i:EventTrigger>
<i:EventTrigger EventName="TextChanged">
<i:Interaction.Behaviors>
<ec:ConditionBehavior>
<ec:ConditionalExpression>
<ec:ComparisonCondition LeftOperand="{Binding Text, ElementName=textBox}" RightOperand="" Operator="Equal"/>
</ec:ConditionalExpression>
</ec:ConditionBehavior>
</i:Interaction.Behaviors>
<ec:ChangePropertyAction PropertyName="Background" Value="Transparent" />
</i:EventTrigger>
</i:Interaction.Triggers>

Answer 1

This should be fairly easy to accomplish with a custom behavior. Use this link to create a behavior that can be attached to a TextBox control. In the OnAttached method, you can handle the TextChanged event of even the LostFocus method to check whether the TextBox is empty or not. Accordingly, you can switch the style between the styles.
P.S: You might need to call the TextBox.ApplyTemplate() method after changing the style. Note sure about that though.

Answer 2

Create your styles
<Style x:Key="FilledStyle" TargetType="TextBox">
<Setter Property="Background" Value="Beige" />
</Style>
<Style x:Key="EmptyStyle" TargetType="TextBox">
<Setter Property="Background" Value="Yellow" />
</Style>
<Models:TextStyleConverter x:Key="TextStyleConverter" />
Create Converter
public class TextStyleConverter : IValueConverter
{
#region Implementation of IValueConverter
/// <summary>
/// Modifies the source data before passing it to the target for display in the UI.
/// </summary>
/// <returns>
/// The value to be passed to the target dependency property.
/// </returns>
/// <param name="value">The source data being passed to the target.</param><param name="targetType">The <see cref="T:System.Type"/> of data expected by the target dependency property.</param><param name="parameter">An optional parameter to be used in the converter logic.</param><param name="culture">The culture of the conversion.</param>
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var val = value as string;
if (String.IsNullOrEmpty(val)) return Application.Current.Resources["EmptyStyle"];
return Application.Current.Resources["FilledStyle"];
}
/// <summary>
/// Modifies the target data before passing it to the source object. This method is called only in <see cref="F:System.Windows.Data.BindingMode.TwoWay"/> bindings.
/// </summary>
/// <returns>
/// The value to be passed to the source object.
/// </returns>
/// <param name="value">The target data being passed to the source.</param><param name="targetType">The <see cref="T:System.Type"/> of data expected by the source object.</param><param name="parameter">An optional parameter to be used in the converter logic.</param><param name="culture">The culture of the conversion.</param>
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
#endregion
}
Usage
<TextBox x:Name="locationtbx" Style="{Binding ElementName=locationtbx, Path=Text, Converter={StaticResource TextStyleConverter}}" />