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

XAML files can have C# source files associated with it referred to as by "code-behind". Code-behind is used to access named controls and handle events for its associated XAML. When using an IDE, you can find this file in the Solution Explorer as a sub-item of the .axaml file.

To change the code-behind for MainView:

• Open the MainView.axaml.cs file

You should see C# code like this:

using Avalonia.Controls;

namespace GetStartedApp.Views;
public partial class MainView : UserControl
{
    public MainView()
    {
        InitializeComponent();
    }
}

The partial class MainView corresponds to the UserControl created by Avalonia as a result of the XAML you already have. The namespace and class name must be the same in both XAML and code-behind. You can find this class name in the root XAML tag:

<UserControl x:Class="GetStartedApp.Views.MainView"
    ...>
</UserControl>

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

• Locate the MainView constructor in the code-behind file (see above instructions).
• After the constructor, add the following code:

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

This will require the following 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 Grid.Row="2" Grid.Column="1" Margin="0,5" Click="ButtonClicked">
    Calculate
</Button>

• 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 controls at runtime.