Re: "...does not inhert IExternalCommand"

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Autodesk.Revit.DB;
using Autodesk.Revit.UI;
using Autodesk.Revit.Attributes;
using Autodesk.Revit.DB.Structure;

namespace MyFirstCommand
{
    [TransactionAttribute(TransactionMode.Manual)]
    public partial class UserControl1 : IExternalCommand
    {
        
        public UserControl1()
        {
            InitializeComponent();
        }

        public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
        {

            return Result.Succeeded;
        
        }

        private void Button1_Click(object sender, RoutedEventArgs e)
        {
            if (Hellobtn.IsChecked == true)
            {
                MessageBox.Show("Hello!");
            }

            else if (Goodbyebtn.IsChecked == true)
            {
                MessageBox.Show("Goodbye!");
            }


        }



    }
}

UserControl1.cs above:

UserControl1.xaml under:

Window x:Class="MyFirstCommand.UserControl1"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:MyFirstCommand"
             mc:Ignorable="d" 
             Height="223.5" Width="615.5"><Grid Margin="2,10,0,0"><Button x:Name="button1" Content="Click here" HorizontalAlignment="Left" VerticalAlignment="Top" Width="134" Margin="273,48,0,0" Height="28" Click="Button1_Click"/><RadioButton x:Name="Hellobtn" Content="Hello" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="185,112,0,0"/><RadioButton x:Name="Goodbyebtn" Content="Goodbye" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="430,112,0,0"/></Grid></Window>