Events in XAML

Most modern UI frameworks are event driven and so is WPF. All of the controls, including the Window (which also inherits the Control class) exposes a range of events that you may subscribe to. You can subscribe to these events, which means that your application will be notified when they occur and you may react to that.
There are many types of events, but some of the most commonly used are there to respond to the user's interaction with your application using the mouse or the keyboard. On most controls you will find events like KeyDown, KeyUp, MouseDown, MouseEnter, MouseLeave, MouseUp and several others.
We will look more closely at how events work in WPF, since this is a complex topic, but for now, you need to know how to link a control event in XAML to a piece of code in your Code-behind file. Have a look at this example:

<Window x:Class="WpfTutorialSamples.XAML.EventsSample"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="EventsSample" Height="300" Width="300">
        <Grid Name="pnlMainGrid" MouseUp="pnlMainGrid_MouseUp" Background="LightBlue">        
                
    </Grid>
</Window>

 Notice how we have subscribed to the MouseUp event of the Grid by 
writing a method name. This method needs to be defined in code-behind, 
using the correct event signature. In this case it should look like 
this:

private void pnlMainGrid_MouseUp(object sender, MouseButtonEventArgs e)
{
        MessageBox.Show("You clicked me at " + e.GetPosition(this).ToString());
}

The MouseUp event uses a delegate called MouseButtonEventHandler,
 which you subscribe to. It has two parameters, a sender (the control 
which raised the event) and a MouseButtonEventArgs object that will 
contain useful information. We use it in the example to get the position
 of the mouse cursor and tell the user about it.

  Fortunately, Visual Studio can help us to generate a correct event 
handler for an event. The easiest way to do this is to simply write the 
name of the event in XAML and then let the IntelliSense of VS do the 
rest for you: