Templated Control doesn't appear

[geometrikal]

I'm trying to create a TemplatedControl for the first time, but it just doesn't appear. Any ideas what I am doing wrong?

axaml:

<Styles xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:controls="using:my_project.Controls">
    <Design.PreviewWith>
        <controls:Alert />
    </Design.PreviewWith>

    <Style Selector="controls|Alert">
        <!-- Set Defaults -->
        <Setter Property="Template">
            <ControlTemplate>
                <Grid IsVisible="True" Background="#40000000">
                    <Border Height="120" Width="200" Background="#EEEEEE" CornerRadius="{TemplateBinding CornerRadius}">
                        <StackPanel Spacing="16" Orientation="Vertical" HorizontalAlignment="Center" VerticalAlignment="Center" >
                            <TextBlock Text="{TemplateBinding Title}" />
                        </StackPanel>
                    </Border>
                </Grid>
            </ControlTemplate>
        </Setter>
    </Style>
</Styles>

axaml.cs:

using Avalonia;
using Avalonia.Controls.Primitives;
using Avalonia.Data;

namespace my_project.Controls
{
    public class Alert : TemplatedControl
    {
        public static readonly DirectProperty<Alert, string> TitleProperty =
            AvaloniaProperty.RegisterDirect<Alert, string>(
                nameof(Thickness), 
                o => o.Title,
                (o, v) => o.Title = v, 
                defaultBindingMode: BindingMode.OneWay);

        private string title;
        public string Title
        {
            get => title;
            set => SetAndRaise(TitleProperty, ref title, value);
        }
    }
}

Main window:

...
<control:Alert Title="this is a test"/>
...

[maxkatz6]

Have you included style from "axaml" in your app? With StyleInclude.

[geometrikal]

@maxkatz6 Thanks that was it.

For anyone else:
Under Application.Styles in App.axaml you need to add something like this (avares = avalonia resource):

<StyleInclude Source = "avares://my_project/Controls/Alert.axaml" />

[Kruno313]

Today, 2024 with Avalonia 11.1.0 the template for Templated control does not use <Style> anymore. See Problem using TemplatedControl #16447.
So, the using in app.axaml is also different:

<Application.Resources>
	<ResourceDictionary>
		<ResourceDictionary.MergedDictionaries>
			<ResourceInclude Source="/Controls/TemplatedControl1.axaml"/>
		</ResourceDictionary.MergedDictionaries>
		. . .
	</ResourceDictionary>
</Application.Resources>

[NickeManarin]

Not working here with 11.1.0:

<Application.Resources>
      <ResourceDictionary>
          <ResourceDictionary.MergedDictionaries>
              <ResourceInclude Source='MyApp.Controls/Themes/ExtendedButton.axaml' />
          </ResourceDictionary.MergedDictionaries>
     </ResourceDictionary>
 </Application.Resources>

I get this error:

App.axaml(15,34): Error AVLN2000 Avalonia: Unable to resolve XAML resource "avares://MyApp/MyApp.Controls/Themes/ExtendedButton.axaml" in the "MyApp" assembly. Make sure this file exists and is public.

I followed the custom templated control example from here, just the difference being the control existing in another assembly.

Btw, in Rider, the Right-click > New > Templated Control still creates a control using the 'Styles' xaml.

[maxkatz6]

I followed the custom templated control example from here, just the difference being the control existing in another assembly.

You need to specify assembly then.

If "MyApp.Controls" is the name of your assembly, then:

<ResourceInclude Source='avares://MyApp.Controls/Themes/ExtendedButton.axaml' />

This doc is about assets, but we use the same URI syntax for resources as well:
https://docs.avaloniaui.net/docs/basics/user-interface/assets#library-assets
Also https://docs.avaloniaui.net/docs/guides/styles-and-resources/resources