DataTemplate

// Selector.idl

import "Selector.idl";

namespace TemplateTest
{
    [default_interface]
    runtimeclass MainWindow : Microsoft.UI.Xaml.Window
    {
        MainWindow();
        Selector Selector;
    }
}

// Selector.h

#pragma once
#include "Selector.g.h"

namespace winrt::TemplateTest::implementation
{
    struct Selector : SelectorT<Selector>
    {
        Selector() = default;

        Windows::UI::Xaml::DataTemplate SelectTemplateCore(IInspectable const& item, Windows::UI::Xaml::DependencyObject const&             container);
        Windows::UI::Xaml::DataTemplate SelectTemplateCore(IInspectable const& item);

        winrt::Windows::UI::Xaml::DataTemplate firstTemplate();
        void firstTemplate(winrt::Windows::UI::Xaml::DataTemplate const& value);

        winrt::Windows::UI::Xaml::DataTemplate secondTemplate();
        void secondTemplate(winrt::Windows::UI::Xaml::DataTemplate const& value);

      private:
        Windows::UI::Xaml::DataTemplate mSelector1;
        Windows::UI::Xaml::DataTemplate mSelector2;
    };
}
namespace winrt::TemplateTest::factory_implementation
{
    struct Selector : SelectorT<Selector, implementation::Selector>
    {
    };
}

//Selector.cpp

#include "pch.h"
#include "Selector.h"
#include "Selector.g.cpp"

namespace winrt::TemplateTest::implementation
{
    Windows::UI::Xaml::DataTemplate Selector::SelectTemplateCore(IInspectable const& item, Windows::UI::Xaml::DependencyObject const& container)
    {
      return mSelector1;
    }

    Windows::UI::Xaml::DataTemplate Selector::SelectTemplateCore(IInspectable const& item)
    {
      return mSelector1;
    }

    winrt::Windows::UI::Xaml::DataTemplate Selector::firstTemplate()
    {
      return this->mSelector1;
    }

    void Selector::firstTemplate(winrt::Windows::UI::Xaml::DataTemplate const& value)
    {
      if (mSelector1 != value) {
           mSelector1 = value;
      }
    }

    winrt::Windows::UI::Xaml::DataTemplate Selector::secondTemplate()
    {
      return this->mSelector2;
    }

    void Selector::secondTemplate(winrt::Windows::UI::Xaml::DataTemplate const& value)
    {
      if (mSelector2 != value) {
        mSelector2 = value;
      }
    }
}

//MainWindow.xaml.h

#pragma once

#include "MainWindow.g.h"
#include "Selector.h"

namespace winrt::TemplateTest::implementation
{
  struct MainWindow : MainWindowT<MainWindow>
  {
    MainWindow();

    winrt::TemplateTest::Selector Selector();
    void Selector(winrt::TemplateTest::Selector const& value);

    private:
        winrt::TemplateTest::Selector mSelector;
   };
}

namespace winrt::TemplateTest::factory_implementation
{
    struct MainWindow : MainWindowT<MainWindow, implementation::MainWindow>
    {
    };
}

//MainWindow.xaml.cpp

namespace winrt::TemplateTest::implementation
{
    MainWindow::MainWindow()
    {
        InitializeComponent();
    }

    winrt::TemplateTest::Selector MainWindow::Selector() {
      return mSelector;
    }

    void MainWindow::Selector(winrt::TemplateTest::Selector const& value) {
      if (mSelector != value) {
        mSelector = value;
      }
    }
}