From MSDN: UnsetValue is a sentinel value that is used for scenarios where the WPF property system is unable to determine a requested DependencyProperty value. UnsetValue is used rather than null reference (Nothing in Visual Basic), because null reference could be a valid property value, as well as a valid (and frequently used) DefaultValue. Which … Read more
You can potentially use the ValueConversionAttribute to determine what types are involved in the converters, and use that information usefully. Look at Piping Value Converters in WPF as an excellent example for the use of ValueConversionAttribute. The example shows how multiple converter classes can be chained, and ValueConversion can be used to pass type info … Read more
According to MSDN – IValueConverter: The data binding engine does not catch exceptions that are thrown by a user-supplied converter. Any exception that is thrown by the Convert method, or any uncaught exceptions that are thrown by methods that the Convert method calls, are treated as run-time errors. Handle anticipated problems by returning DependencyProperty.UnsetValue. The … Read more
IMO, the ConvertBack method is used to convert your visual representation of the data to the specific DataType. For example: you use a Converter to convert a boolean true to the string “TrueBoolean”. This text will be displayed in your TextBox. When you change the value of the TextBox, the ConvertBack method will be called … Read more
Converters always implement IValueConverter. That means a call to Convert or ConvertBack passes a single additional parameter. That parameter is extracted from the XAML. As Hitesh Patel suggests there is nothing to stop you putting more than one value into the parameter, so long as you have a delimiter to separate them out later, but … Read more
I’ve found the simplest and best solution to be this: [ValueConversion(typeof(bool), typeof(Visibility))] public sealed class BoolToVisibilityConverter : IValueConverter { public Visibility TrueValue { get; set; } public Visibility FalseValue { get; set; } public BoolToVisibilityConverter() { // set defaults TrueValue = Visibility.Visible; FalseValue = Visibility.Collapsed; } public object Convert(object value, Type targetType, object parameter, CultureInfo … Read more
@AresAvatar is right in suggesting you use a ValueConverter, but that implementation does not help the situation. This does: public class NullImageConverter :IValueConverter { public object Convert(object value, Type targetType, object parameter, CultureInfo culture) { if (value == null) return DependencyProperty.UnsetValue; return value; } public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) { … Read more
It’s your Returns clause. You have a 4 parameter method that you’re setting up, but you’re only using a 1 parameter lambda. I ran the following without issue: [TestMethod] public void IValueConverter() { var myStub = new Mock<IValueConverter>(); myStub.Setup(conv => conv.Convert(It.IsAny<object>(), It.IsAny<Type>(), It.IsAny<object>(), It.IsAny<CultureInfo>())). Returns((object one, Type two, object three, CultureInfo four) => (int)one + … Read more
Here ya go! <RadioButton Content=”None” xmlns:sys=”clr-namespace:System;assembly=mscorlib”> <RadioButton.IsChecked> <Binding Path=”MyProperty” Converter=”{StaticResource IntToBoolConverter}”> <Binding.ConverterParameter> <sys:Int32>0</sys:Int32> </Binding.ConverterParameter> </Binding> </RadioButton.IsChecked> </RadioButton> The trick is to include the namespace for the basic system types and then to write at least the ConverterParameter binding in element form.
I used this method by Gareth Evans in my Silverlight project. Here’s my implementation of it: public class ValueConverterGroup : List<IValueConverter>, IValueConverter { #region IValueConverter Members public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { return this.Aggregate(value, (current, converter) => converter.Convert(current, targetType, parameter, culture)); } public object ConvertBack(object value, Type targetType, object parameter, … Read more