Lambda Converters

The library allows to create IValueConverter, IMultiValueConverter, DataTemplateSelector, and ValidationRule objects with the most convenient syntax available, ideally, using the lambda expressions.

Lambda Value Converters

First create a (static) class and define your converters as static fields (or properties):

internal static class Converters
{
    public static readonly IValueConverter VisibleIfTrue =
        ValueConverter.Create<bool, Visibility>(e => e.Value ? Visibility.Visible : Visibility.Collapsed);

    public static readonly IValueConverter VisibleIfNotNull =
        ValueConverter.Create<object, Visibility>(e => e.Value != null ? Visibility.Visible : Visibility.Collapsed);

    public static readonly IValueConverter ToUpperCase =
        ValueConverter.Create<string, string>(e => e.Value.ToUpper());
}

You're done! Just reference the converters with the x:Static expressions from your XAML files (assuming that c is the namespace definition for the Converters class):

<Button Visibility="{Binding model.IsAvailable, Converter={x:Static c:Converters.VisibleIfTrue}}" />

<TextBlock Text="{Binding model.Heading, Converter={x:Static c:Converters.ToUpperCase}}" />

Features

• strongly-typed converters
• resource declaration not needed, just use the x:Static expressions
• separate class for each converter not needed anymore
• no redundant declarations: if you do not need the ConvertBack method, don't define it; otherwise, just put the second lambda expression
• full support for the remaining parameters of the Convert and ConvertBack methods: the culture and the parameter (also strongly-typed) are accessible as well
• if the conversion fails due to unexpected value types the optional error strategy can be specified

Lambda Data Template Selectors

The library also allows to create DataTemplateSelector objects in the same convenient way as value converters. In order to define a selector simply write a static field (or property) similar to this snippet:

internal static class TemplateSelector
{
    public static DataTemplateSelector AlternatingText =
        LambdaConverters.TemplateSelector.Create<int>(
            e => e.Item % 2 == 0
                ? (DataTemplate) ((FrameworkElement) e.Container)?.FindResource("BlackWhite")
                : (DataTemplate) ((FrameworkElement) e.Container)?.FindResource("WhiteBlack"));
}

Use your Lambda DataTemplateSelectors by referencing it with the x:Static markup extention (assuming that s is the namespace definition for the TemplateSelector class):

<UserControl.Resources>
    <DataTemplate x:Key="BlackWhite">
        <TextBlock Text="{Binding}" Foreground="Black" Background="White" />
    </DataTemplate>
    <DataTemplate x:Key="WhiteBlack">
        <TextBlock Text="{Binding}" Foreground="White" Background="Black" />
    </DataTemplate>
</UserControl.Resources>
<DockPanel>
    <ListBox ItemsSource="{Binding IntNumbers}"
             ItemTemplateSelector="{x:Static s:TemplateSelector.AlternatingText}">
    </ListBox>
</DockPanel>

Tada! All even numbers from IntNumbers are displayed with black font and white background and the odd numbers get the inverse font and background colors.

Features

• strongly-typed Selectors
• resource declaration not needed, just use the x:Static expressions
• separate class for each selector not needed anymore
• full support for the remaining parameter container. For example, if you need to grab a DataTemplate from where the selector is use (see the example above).

Lambda Validation Rules

Furthermore, you'll get Lambda ValidationRules on top. By now you know "the drill". First, define a ValidationRuleobject like this:

public static class Rule
{
    public static ValidationRule IsNumericString =
        LambdaConverters.Validator.Create<string>(
            e => e.Value.All(char.IsDigit)
                ? ValidationResult.ValidResult
                : new ValidationResult(false, "Text has non-digit characters!"));
}

And then reference your new rule in vour View (assuming that r is the namespace definition for the Rule class):

<TextBox>
    <TextBox.Text>
        <Binding Path="Text" UpdateSourceTrigger="PropertyChanged">
            <Binding.ValidationRules>
                <x:Static Member="r:Rule.IsNumericString"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

Now, you made sure that only strings which consists of digits are passed to your ViewModel.

Features

• strongly-typed rules
• resource declaration not needed, just use the x:Static expressions
• separate class for each rule not needed anymore
• full support for the remaining parameter culture

Installation

Use the NuGet package manager to install the package.

:bulb: ReSharper users: use the Extension Manager to install the external annotations for the library.

Limitations

The library currently supports the WPF only.

Bugs? Questions? Suggestions?

Please feel free to report them.