<Window x:Class="WpfEventTriggerSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" 
        xmlns:vm="clr-namespace:WpfEventTriggerSample.ViewModels"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <vm:MainWindowViewModel x:Key="vmMainWindowViewModel" />
    </Window.Resources>
    <Grid DataContext="{Binding Source={StaticResource vmMainWindowViewModel}}">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Loaded">
                <i:InvokeCommandAction Command="{Binding DoLoadCommand}" 
                                       CommandParameter="I am loaded!" />
            </i:EventTrigger>
        </i:Interaction.Triggers>

        <TextBlock Text="Testing InvokeCommandAction..." 
                   Margin="5" VerticalAlignment="Top" />
    </Grid>
</Window>

using WpfEventTriggerSample.Helper;

namespace WpfEventTriggerSample.ViewModels
{
    public class MainWindowViewModel
    {
        public DelegateCommand<string> DoLoadCommand { set; get; }
        public MainWindowViewModel()
        {
            DoLoadCommand = new DelegateCommand<string>(doLoadCommand, canDoLoadCommand);
        }

        private void doLoadCommand(string param)
        {
            //do something
        }

        private bool canDoLoadCommand(string param)
        {
            return true;
        }
    }
}

<Button>
            <i:Interaction.Triggers>
                <i:EventTrigger EventName="Click">
                    <i:InvokeCommandAction Command="{Binding DoClick}" 
                                       CommandParameter="I am loaded!" />
                </i:EventTrigger>
            </i:Interaction.Triggers>
</Button>

public abstract class Observer
    {
        protected Observable Observable;
        public abstract void Update();
    }

 public  class Observable
    {
        private readonly List<Observer> _observers = new List<Observer>();

        public void Attach(Observer observer)
        {
            _observers.Add(observer);
        }
        public void Dettach(Observer observer)
        {
            _observers.Remove(observer);
        }

        public void NotifyAllObservers()
        {
            foreach (var observer in _observers)
            {
                observer.Update();
            }
        }
    }

 public  class Switch:Observable
    {
        private bool _state;

        public bool ChangeState
        {
            set
            {
                _state = value;
                NotifyAllObservers();
            }
            get { return _state; }
        }
    }

   public class RedLED:Observer
    {
        private bool _on = false;
        public override void Update()
        {
            _on = !_on;
            Console.WriteLine($"Red LED is {((_on) ? "On" : "Off")}");
        }
    }

  public class GreenLED:Observer
    {
        private bool _on = false;
        public override void Update()
        {
            _on = !_on;
            Console.WriteLine($"Green LED is {((_on) ? "On" : "Off")}");
        }
    }

  public  class BlueLED:Observer
    {
        private bool _on = false;
        public override void Update()
        {
            _on = !_on;
            Console.WriteLine($"Blue LED is {((_on) ? "On" : "Off")}");
        }
    }

var greenLed=new GreenLED();
            var redLed=new RedLED();
            var blueLed=new BlueLED();

            var switchKey=new Switch();
            switchKey.Attach(greenLed);
            switchKey.Attach(redLed);
            switchKey.Attach(blueLed);

            switchKey.ChangeState = true;
            switchKey.ChangeState = false;

Green LED is On
Red LED is On
Blue LED is On
Green LED is Off
Red LED is Off
Blue LED is Off