您能否在 xaml 中的属性绑定上调用多个转换器，如果可以，如何调用

Question

I have a button defined in xaml whose visibility is bound to a dependency property using the standard BooleanToVisibility converter like so.

 Visibility="{Binding Path=GoToButtonVisibility,Converter={StaticResource booltovis}, RelativeSource={RelativeSource TemplatedParent}}"

Now I also have a textbox whose read only property I would like to bind to the visibility of the button I mentioned above, except that it needs to be the opposite, so if the button isn't visible it's read only will be true, if not it will be false.

That meant I needed some way of having Not x in my xaml. Stack overflow to the rescue with this answer.

So now I have a nice NotConverter, however I cant simply do something like this;

 IsReadOnly="{Binding ElementName=PART_GoToButton, Path=Visibility, Converter={StaticResource NotConverter}}"

because the NotConverter will throw an invalid cast exception. I have no problem with that and I understand why. I do however like the principle of the not converter so my question(s) are as follows.

1) in the xaml itself is it possible to invoke both converters on the same like such that they would produce the desired result. 2) assuming 1 isn't possible then it suggests the need for a visibility to Boolean convertor. As the BooleanToVisibility converter is builtin I'm not sure how the convert and Convertback functions have been written and therefore how I would effectively reverse them. Any ideas?

Answer 1

Just bind to the same property, but through your not converter. Your code for the text box would thus be:

 IsReadOnly="{Binding Path=GoToButtonVisibility, Converter={StaticResource NotConverter}}"

Your NotConverter is this:

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value != null && value is bool)
            return !(bool)value;
        else
            return null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value != null && value is bool)
        {
            return !(bool)value;
        }

        return null;
    }

There's no need to get the visibility of the button from the UI.

Answer 2

you can create an aggregate converter like this:

   public class ValueConverterGroup : List<IValueConverter>, IValueConverter
   {
    #region IValueConverter Members

    public object Convert(object value, Type targetType, object parameter, string language)
    {
      return this.Aggregate(value, (current, converter) => converter.Convert(current, targetType, parameter, language));
    }

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

    #endregion

then combine converters in xaml:

<conv:ValueConverterGroup x:Key="booleanToInvertedVisibilityConverter">
  <conv:BooleanNegationConverter />
  <conv:BooleanToVisibilityConverter />
</conv:ValueConverterGroup>

and then use that aggregate converter just as you would use any other:

             <Button Name="btnBuy" Content="Buy full version" Command="{Binding Path=CommandBuy}" HorizontalAlignment="Center" 
                Visibility="{Binding Path=IsPaidVersion, Converter={StaticResource booleanToInvertedVisibilityConverter}}"/>

Answer 3

Using the aggregate converter described in @Jogy's answer you can even use the following markup extension :

[MarkupExtensionReturnType(typeof(IValueConverter))]
public class ConverterChainExtension : MarkupExtension
{
    public ConverterChainExtension()
    {
    }

    public ConverterChainExtension(string converterNames)
    {
        this.ConverterNames = converterNames;
    }

    public string Separator { get; set; }

    [ConstructorArgument("converterNames")]
    public string ConverterNames { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        List<IValueConverter> converters = new List<IValueConverter>();
        if (this.ConverterNames != null)
        {
            foreach (string converterName in this.ConverterNames.Split(new[] { this.Separator }, StringSplitOptions.RemoveEmptyEntries))
            {
                if (new StaticResourceExtension(converterName).ProvideValue(serviceProvider) is IValueConverter converter)
                {
                    converters.Add(converter);
                }
                else
                {
                    throw new InvalidOperationException($"Couldn't find the converter with name : '{converterName}'");
                }
            }
        }

        return new YourAggregateConverter(converters);
    }
}

After declaring the converters you want as resources ( BoolInverterConverter and BoolToVisibilityConverter ), you can use the markup extension like this :

<Button Visibility="{Binding SomeProperty, Converter={ConverterChain Separator=/, ConverterNames=BoolInverterConverter/BoolToVisibilityConverter}}"/>