[Proposal] Math Expression Converters

MathExpressionConverter

• Proposed
• Prototype
• Implementation
  • iOS Support
  • Android Support
  • macOS Support
  • Windows Support
• Unit Tests
• Sample
• Documentation: https://github.com/MicrosoftDocs/CommunityToolkit/pull/89

Summary

The MathExpressionConverter is a converter that allows users to calculate an expression at runtime from supplied arguments.

Detailed Design

MathExpression.shared.cs

sealed class MathExpression
{
  internal MathExpression(string expression, IEnumerable<double>? arguments = null);

  public double Calculate();
}

MathExpressionConverter.shared.cs

public class MathExpressionConverter : ValueConverterExtension, IValueConverter
{
  public object? Convert(object? value, Type? targetType, object? parameter, CultureInfo culture)
  {
	if (parameter is not string expression)
		throw new ArgumentException("The parameter should be of type String.");

	if (value == null || !double.TryParse(value.ToString(), out var xValue))
		return null;

	var math = new MathExpression(expression, new[] { xValue });

	var result = math.Calculate();
	return result;
  }

  public object ConvertBack(object? value, Type? targetType, object? parameter, CultureInfo? culture) => throw new NotImplementedException();
}

MathOperator.shared.cs

sealed class MathOperator
{
  public string Name { get; }
  
  public int NumericCount { get; }
  
  public MathOperatorPrecedence Precedence { get; }
  
  public Func<double[], double> CalculateFunc { get; }
  
  public MathOperator(
	  string name,
	  int numericCount,
	  MathOperatorPrecedence precedence,
	  Func<double[], double> calculateFunc)
  {
	  Name = name;
	  CalculateFunc = calculateFunc;
	  Precedence = precedence;
	  NumericCount = numericCount;
  }
}

MultiMathExpressionConverter.shared.cs

public class MultiMathExpressionConverter : MultiValueConverterExtension, IMultiValueConverter
{
  public object? Convert(object[]? values, Type? targetType, object? parameter, CultureInfo culture)
  {
	if (parameter is not string expression)
		throw new ArgumentException("The parameter should be of type String.");

	if (values == null)
		return null;

	var args = new List<double>();
	foreach (var value in values)
	{
		if (value == null)
			return null;

		if (double.TryParse(value.ToString(), out var xValue))
		{
			args.Add(xValue);
		}
	}

	var math = new MathExpression(expression, args);

	var result = math.Calculate();
	return result;
  }

  public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) => throw new NotImplementedException();
}

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:MathExpressionConverter x:Key="MathExpressionConverter" />
             <xct:MultiMathExpressionConverter x:Key="MultiMathExpressionConverter" />
         </ResourceDictionary>
    </ContentPage.Resources>

    <StackLayout>

        <Frame
           x:Name="CalculatedFrame"
           HeightRequest="120"
           CornerRadius="{Binding Source={x:Reference CalculatedFrame}, Path=HeightRequest, Converter={StaticResource MathExpressionConverter}, ConverterParameter='x/2'}">

        <Label TextColor="Black">
            <Label.Text>
                <MultiBinding Converter="{StaticResource MultiMathExpressionConverter}"
                              ConverterParameter="x0 * x1"
                              StringFormat="The area of Frame = {0}">
                    <Binding Path="{Binding Source={x:Reference CalculatedFrame}, Path=HeightRequest}" />
                    <Binding Path="{Binding Source={x:Reference CalculatedFrame}, Path=WidthRequest}" />
                </MultiBinding>
            </Label.Text>
        </Label>

    </StackLayout>
</ContentPage>

C# Usage

new Frame().Size(120, -1).Assign(out var frame)
  .Bind(Frame.CornerRadiusProperty, nameof(Frame.HeightRequest), converter = new MathExpressionConverter(), converterParameter: "x/2", source: frame);

[VladislavAntonyuk]

@russnash It’s yours. Thank you!

[msftbot[bot]]

Reopening Proposal.

Only Proposals moved to the Closed Project Column and Completed Project Column can be closed.