Extending NoesisGUI

Being based in XAML, NoesisGUI is a framework that can be extended in many ways. For example, you can create your own Converters, Commands, CustomControls, UserControls or code-behind classes. This tutorial is focused on the steps that have to be performed to extend NoesisGUI using your own classes.


First thing we are going to do is writing a very simple XAML with a TextBox where you can write text and a TextBlock that outputs the text you write filtered through a converter. The converter we are going to implement transforms the input to upper case.

    <local:UppercaseConverter x:Key="Converter"/>
  <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" Background="Blue">
    <TextBox x:Name="Input" Width="100"/>
    <TextBlock Text="{Binding Text, ElementName=Input, Converter={StaticResource Converter}}"

The highlighted line remarks where the extended class, in this case under the namespace Sample, is being used. If this XAML is used as it is, we will receive a warning indicating that the type Sample.UppercaseConverter is not known. We need to implement a new class registered with this name. Let's see how to do this in both C++ and C# languages.

Extending in C++

#include <NsCore/Noesis.h>
#include <NsCore/TypeOf.h>
#include <NsCore/RegisterComponent.h>
#include <NsCore/ReflectionImplement.h>
#include <NsGui/BaseValueConverter.h>

using namespace Noesis;

namespace Sample
    class UppercaseConverter final: public BaseValueConverter
        bool TryConvert(BaseComponent* value, const Type* targetType, BaseComponent* /*parameter*/,
            Ptr<BaseComponent>& result) override
            if (targetType == TypeOf<NsString>() && Boxing::CanUnbox<NsString>(value))
                NsString text = Boxing::Unbox<NsString>(value);
                result = Boxing::Box<NsString>(text);
                return true;

            return false;

        NS_IMPLEMENT_INLINE_REFLECTION_(UppercaseConverter, BaseValueConverter, "Sample.UppercaseConverter")

The code shown above illustrates the key points that are needed to implement a new class:

  • New classes must always derive from their corresponding base class. In this case the base class is BaseValueConverter because we are interested in the IValueConverter interface.
  • The new class must implement the required methods. BaseValueConverter requires us to implement TryConvert and TryConvertBack, but in this specific sample, conversion in only one direction, we only need implementing TryConvert. It is implemented by unboxing the text, converting to uppercase and returning the boxed object.
  • And last, reflection tags must be added to our new class:
NS_IMPLEMENT_INLINE_REFLECTION_(UppercaseConverter, BaseValueConverter, "Sample.UppercaseConverter")

Here we are indicating that our class UppercaseConverter derives from BaseValueConverter and is registered with the name 'UppercaseConverter' under the namespace 'Sample'. This is the identifier that XAMLs will be using to reference this native class.

Before using this class inside a XAML it must be registered in the component factory. This must be done after Noesis initialization and before loading the corresponding XAML. Our application framework provides a virtual function that can be used for this purpose:

class AppLauncher final: public ApplicationLauncher
    void RegisterComponents() const override

Once the class is properly registered, the XAML will load without errors and our converter will accordingly be used.


Extending in C#

Everything is easier in C# because the registration is automatically done internally and we don't need to apply reflection macros because reflection is already supported out of the box. You just need to create the class UppercaseConverter under the namespace Sample and implement the IValueConverter interface.

using System;
using System.Globalization;
using Noesis;

namespace Sample
    public class UppercaseConverter : IValueConverter
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
            return ((string)value).ToUpper();
        public object ConvertBack(object value, Type targetType, object parameter,
            CultureInfo culture)
            return null;
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