Markup extension not found

Question

I was studying the documentation found in the microsoft page because i'm willing to learn xamarin.forms. Whenever a new topic is introduced i try to write a small application that puts to test what i've just learned. While experimenting with xaml markup extensions i found out that one of the examples shown in the microsoft documentation doesn't work for me, not even when i copy it from the website and paste it in my vs project.

The C# code is this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace XamarinLab
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }
    }

    public class HslColorExtension : IMarkupExtension<Color>
    {
        public double H { set; get; }

        public double S { set; get; }

        public double L { set; get; }

        public double A { set; get; } = 1.0;

        public Color ProvideValue(IServiceProvider serviceProvider)
        {
            return Color.FromHsla(H, S, L, A);
        }

        object IMarkupExtension.ProvideValue(IServiceProvider serviceProvider)
        {
            return (this as IMarkupExtension<Color>).ProvideValue(serviceProvider);
        }
    }
}

and the xaml code is

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:XamarinLab"
             x:Class="XamarinLab.MainPage">

    <ContentPage.Resources>
        <ResourceDictionary>
            <Style TargetType="BoxView">
                <Setter Property="WidthRequest" Value="80" />
                <Setter Property="HeightRequest" Value="80" />
                <Setter Property="HorizontalOptions" Value="Center" />
                <Setter Property="VerticalOptions" Value="CenterAndExpand" />
            </Style>
        </ResourceDictionary>
    </ContentPage.Resources>

    <StackLayout>
        <BoxView>
            <BoxView.Color>
                <local:HslColorExtension H="0" S="1" L="0.5" A="1" />
            </BoxView.Color>
        </BoxView>

        <BoxView>
            <BoxView.Color>
                <local:HslColor H="0.33" S="1" L="0.5" />
            </BoxView.Color>
        </BoxView>

        <BoxView Color="{local:HslColorExtension H=0.67, S=1, L=0.5}" />

        <BoxView Color="{local:HslColor H=0, S=0, L=0.5}" />

        <BoxView Color="{local:HslColor A=0.5}" />
    </StackLayout>

 </ContentPage>

when i try to run the app the following exception pops up

markup extension not found for local:HslColorExtension

The example i copied is found at : https://learn.microsoft.com/it-it/xamarin/xamarin-forms/xaml/markup-extensions/creating

It's the very first example, thanks in advance for any help.

Answer 1

You need to create a new File Class, called HslColorExtensionin your project, rather than creating a class in the MainPage file, where it won't recognize the namespace or the class created.

Just move that part to a new File and you should be all set up.

You can check the Offical Sample, to see the structure, the files and how to setup.