Respond to an Event

There are a number of ways you can implement actions in an Avalonia application. On this page, you will see how to use one of the simplest: how to write event handling code for a button click.

To start, you will write a button click event handler that does not interact with any of the other controls.

Code-behind

The XAML file for the main window has a C# code-behind file associated with it. If you're using an IDE, you can find this file in the Solution Explorer - it is a sub-item of the .axaml file.

To change the code-behind for the main window:

• Open the MainWindow.axaml.cs file

You will see some C# code like this:

using Avalonia.Controls;

namespace GetStartedApp
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }
}

The partial class MainWindow corresponds to the window object that is created by Avalonia UI as a result of the XAML you already have. You can find this class name in the XAML window tag:

<Window 
    ...
    x:Class="GetStartedApp.MainWindow" >
</Window>

To add an event handler for the button, follow this procedure:

• Locate the MainWindow constructor in the code-behind file for the main window (see above instructions).
• After the constructor add the following code:

public void ButtonClicked(object source, RoutedEventArgs args)
{
    Debug.WriteLine("Click!");
}

This will require some additional using statements:

using Avalonia.Interactivity;
using System.Diagnostics;

• Switch to the XAML file and locate the <Button> tag.
• Enter the click attribute at the end of the tag, as follows:

<Button
   ...
   Click="ButtonClicked">
</Button>

tip

If you're using an IDE you will see the Avalonia UI Intellisense as you type.

• Run the app and click the button.

You should see the result on the Output window for Debug, like this:

On the next page, you will see how to use code-behind to read and change the properties of Avalonia UI controls at runtime.