ColorToBlackOrWhiteConverter

Article
03/01/2023

The ColorToBlackOrWhiteConverter is a one way converter that allows users to convert an incoming Color to a monochrome value of either Colors.Black or Colors.White.

The Convert method returns the supplied value converted to either Colors.Black or Colors.White based on whether the supplied value is considered dark or not. A Color is considered when its red, green and blue components each average less than 127.

The ConvertBack method is not supported.

BaseConverter Properties

The following properties are implemented in the base class, public abstract class BaseConverter:

Property	Description
`DefaultConvertReturnValue`	Default value to return when `IValueConverter.Convert(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.
`DefaultConvertBackReturnValue`	Default value to return when `IValueConverter.ConvertBack(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.

ICommunityToolkitValueConverter Properties

The following properties are implemented in the public interface ICommunityToolkitValueConverter:

Property	Type	Description
`DefaultConvertReturnValue`	`object?`	Default value to return when `IValueConverter.Convert(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.
`DefaultConvertBackReturnValue`	`object?`	Default value to return when `IValueConverter.ConvertBack(object?, Type, object?, CultureInfo?)` throws an `Exception`. This value is used when CommunityToolkit.Maui.Options`.ShouldSuppressExceptionsInConverters` is set to `true`.

Syntax

XAML

Including the XAML namespace

In order to use the toolkit in XAML the following xmlns needs to be added into your page or view:

xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"

Therefore the following:

<ContentPage
    x:Class="CommunityToolkit.Maui.Sample.Pages.MyPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml">

</ContentPage>

Would be modified to include the xmlns as follows:

<ContentPage
    x:Class="CommunityToolkit.Maui.Sample.Pages.MyPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit">

</ContentPage>

Using the ColorToBlackOrWhiteConverter

The ColorToBlackOrWhiteConverter can be used as follows in XAML:

<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
             x:Class="CommunityToolkit.Maui.Sample.Pages.Converters.ColorToBlackOrWhiteConverterPage">

    <ContentPage.Resources>
        <ResourceDictionary>
            <toolkit:ColorToBlackOrWhiteConverter x:Key="ColorToBlackOrWhiteConverter" />
        </ResourceDictionary>
    </ContentPage.Resources>

    <Label Text="The Text is showing in monochrome"
           TextColor="{Binding AppTextColor, Converter={StaticResource ColorToBlackOrWhiteConverter}}" />

</ContentPage>

C#

The ColorToBlackOrWhiteConverter can be used as follows in C#:

class ColorToBlackOrWhiteConverterPage : ContentPage
{
    public ColorToBlackOrWhiteConverterPage()
    {
        var label = new Label { Text = "The Text is showing in monochrome" };

        label.SetBinding(
            Label.TextColorProperty,
            new Binding(
                static (ViewModel vm) => vm.AppTextColor,
                converter: new ColorToBlackOrWhiteConverter()));

        Content = label;
    }
}

C# Markup

Our CommunityToolkit.Maui.Markup package provides a much more concise way to use this converter in C#.

using CommunityToolkit.Maui.Markup;

class ColorToBlackOrWhiteConverterPage : ContentPage
{
    public ColorToBlackOrWhiteConverterPage()
    {
        Content = new Label { Text = "The Text is showing in monochrome" }
            .Bind(
                Label.TextColorProperty,
                static (ViewModel vm) => vm.AppTextColor,
                converter: new ColorToBlackOrWhiteConverter());
    }
}

Examples

You can find an example of this converter in action in the .NET MAUI Community Toolkit Sample Application.

API

You can find the source code for ColorToBlackOrWhiteConverter over on the .NET MAUI Community Toolkit GitHub repository.

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