Can I change the properties of a binding in a DataTrigger, without knowing the binding itself?

Question

I have a TextBox style that formats a number if the box is unfocused, but leaves the number unformatted whlie it\'s being edited.

This is the style I wa

Answer 1

Is there a way I can make this style generic, such as only changing the StringFormat property of the binding in the DataTrigger?

Inherit Style and new XAML would become this:

 <TextBox>
    <TextBox.Style>
        <local:FlyingStyle Binding="{Binding ElementName=This, Path=SomeValue}" StringFormat="F2" />
    </TextBox.Style>
 </TextBox>

Here's the class...

public class FlyingStyle : Style
{
    public FlyingStyle()
        : base(typeof(TextBox))
    { }

    string _stringFormat;
    public string StringFormat
    {
        get { return _stringFormat; }
        set
        {
            _stringFormat = value;
            CheckInitialize();
        }
    }
    Binding _binding;
    public Binding Binding
    {
        get { return _binding; }
        set
        {
            _binding = value;
            CheckInitialize();
        }
    }
    void CheckInitialize()
    {
        if (StringFormat == null || Binding == null) { return; }// need both

        Setters.Add(CreateSetter(Binding, StringFormat));

        var trigger = new Trigger
        {
            Property = UIElement.IsKeyboardFocusWithinProperty,
            Value = true,
        };
        trigger.Setters.Add(CreateSetter(Binding));
        Triggers.Add(trigger);
    }

    /// <summary>Creates the common <see cref="Setter"/>.</summary>
    static Setter CreateSetter(Binding binding, string stringFormat = null)
    {
        // must create a copy, because same binding ref but diff StringFormats
        var bindingCopy = new Binding
        {
            // these could be copies as well
            UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged,
            ValidatesOnDataErrors = true,
            Mode = BindingMode.TwoWay,
            Path = binding.Path,

            AsyncState = binding.AsyncState,
            BindingGroupName = binding.BindingGroupName,
            BindsDirectlyToSource = binding.BindsDirectlyToSource,
            Converter = binding.Converter,
            ConverterCulture = binding.ConverterCulture,
            ConverterParameter = binding.ConverterParameter,
            ElementName = binding.ElementName,
            FallbackValue = binding.FallbackValue,
            IsAsync = binding.IsAsync,
            NotifyOnSourceUpdated = binding.NotifyOnSourceUpdated,
            NotifyOnTargetUpdated = binding.NotifyOnTargetUpdated,
            NotifyOnValidationError = binding.NotifyOnValidationError,
            //StringFormat = set below...
            TargetNullValue = binding.TargetNullValue,
            UpdateSourceExceptionFilter = binding.UpdateSourceExceptionFilter,
            ValidatesOnExceptions = binding.ValidatesOnExceptions,
            XPath = binding.XPath,
            //ValidationRules = binding.ValidationRules
        };
        // mutex ElementName, so modify if needed
        // Source = binding.Source,
        // RelativeSource = binding.RelativeSource,

        if (stringFormat != null)
        {
            bindingCopy.StringFormat = stringFormat;
        }
        return new Setter(TextBox.TextProperty, bindingCopy);
    }
}

Note that my test was

• the generic MainWindow
• impl INotifyPropertyChanged
• SomeValue INPC property
• DataContext = this
• x:Name = This

Answer 2

My attempt to solve this ended up with a custom control plus a multi-binding, both of which where suggested above.

This allowed me to use markup like this:

< CustomTextBox Value="{Binding Value"} Format="N2" />

I tried to post my code but I keep getting an error about "code that is not properly formatted as code".

Answer 3

I'm wondering if you could maybe have an attached property on the edits to hold the formatted value (just bound to the real edit value with a Stringformat applied), then in your out of focus trigger you could set the edit value to this property.

This would result in a circular binding though when the edit doesn't have focus, dunno how WPF reacts in such situations.

Answer 4

The only option I see there would be to create an attached property for the StringFormat and use a multiBinding.

Not quite what you wanted, but close enough, I guess...

you have more info on this (kind of duplicate) question on S.O.:

Modifying the Parameters of a TextBox's Text Binding through the use of a Style

Answer 5

Sadly this is (to my knowledge) not possible. One possible workaround would be programmatically creating such a style on the fly, that could be encapsulated in a MarkupExtension which takes the path as constructor parameter.