[Proposal] `bool`-to-`object` Converter

BoolToObjectConverter

• Proposed
• Prototype
• Implementation
  • iOS Support
  • Android Support
  • macOS Support
  • Windows Support
• Unit Tests
• Documentation
• Sample

Summary

The BoolToObjectConverter is a converter that allows users to convert a bool value binding to a specific object. By providing both a TrueObject and a FalseObject in the converter the appropriate object will be used depending on the value of the binding

Detailed Design

public class BoolToObjectConverter : BoolToObjectConverter<object>
{
}

public class BoolToObjectConverter<TObject> : ValueConverterExtension, IValueConverter
{
  public TObject? TrueObject { get; set; }
  public TObject? FalseObject { get; set; }

  public object? Convert(object? value, Type? targetType, object? parameter, CultureInfo? culture)
  {
	  if (value is bool result)
		  return result ? TrueObject : FalseObject;
  
	  throw new ArgumentException("Value is not a valid boolean", nameof(value));
  }

  public object ConvertBack(object? value, Type? targetType, object? parameter, CultureInfo? culture)
  {
	  if (value is TObject result)
		  return result.Equals(TrueObject);
  
	  if (default(TObject) == null && value == null && TrueObject == null)
		  return true;
  
	  throw new ArgumentException($"Value is not a valid {typeof(TObject).Name}", nameof(value));
  }
}

Usage Syntax

XAML Usage

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:xct="http://xamarin.com/schemas/2020/toolkit"
             x:Class="MyLittleApp.MainPage">

    <ContentPage.Resources>
         <ResourceDictionary>
             <xct:BoolToObjectConverter x:Key="BoolToObjectConverter" TrueObject="16" FalseObject="10" />
         </ResourceDictionary>
    </ContentPage.Resources>

    <StackLayout>

        <Label Text="Hi there from the Docs!" FontSize="{Binding MyBoolean, Converter={StaticResource BoolToObjectConverter}}" />

    </StackLayout>
</ContentPage>

C# Usage

class MyPage : ContentPage
{
    public MyPage()
    {
        Content = new Label { Text = "Hi there from the Docs!"}
                          .Bind(Label.FontSizeProperty, nameof(ViewModel.MyBoolean), converter: new BoolToObjectConverter<double>{ FalseObject = 10, TrueObject = 16 })
    }
}

[brminnick]

[jfversluis]

Happy now?!