How to run you application from Avalonia source

[llfab]

In some edge cases I wanted to run my Avalonia application such that I can:

• debug into Avalonia code
• set break points in Avalonia code
• potentially patch something in Avalonia code
• while being able to debug my own code

@kekekeks gave an example how to be able to debug Avalonia code using a local package: #14446 (comment)

I however wanted to have a pure code only solution. I came up with this proposal here that works for me: https://github.com/llfab/Samples/tree/main/AvaloniaAnimationTest

These are the principles:

Put all Avalonia package references in .props files

I would propose that independent of being able to build from source such that you can centrally switch your Avalonia version.

The "root" .props file:

<?xml version="1.0" encoding="utf-8"?>
<Project>
  <PropertyGroup>
    <AvaloniaVersion>11.0.9</AvaloniaVersion>
  </PropertyGroup>

  <PropertyGroup>
    <BuildAvaloniaFromSource>false</BuildAvaloniaFromSource>
	<!-- run (on Windows): subst A: <AvaloniaRootFolder> to make this reference work -->
    <AvaloniaRootFolder>A:</AvaloniaRootFolder>	
  </PropertyGroup>

  <PropertyGroup Condition="'$(BuildAvaloniaFromSource)' == 'true'">
    <IncludeAvaloniaGenerators>true</IncludeAvaloniaGenerators>
  </PropertyGroup>

</Project>

This specifies the version if Avalonia is consumed from nuget. For building from source there is a single switch BuildAvaloniaFromSource that you will need to set to true. Note that IncludeAvaloniaGenerators must be set to true too, if you want to correctly build from source.
These props are all relative somewhere in my repository. To have the proper folder reference to the local Avalonia repository, the only solution I found, that would be independent of how a developer sets up his folders, is this:

• set your Avalonia root folder as an unused drive letter (on Windows)
• set that drive letter to your local Avalonia folder using the subst command
  In this props file, of course, you could set the actual path on your machine. The problem is, that you cannot use such tricks in you solution file that also must contain the Avalonia projects. Environment variables do not work in sln files.
• For Linux and MacOS there may be a similar option

The .props file for libraries consuming Avalonia:

<?xml version="1.0" encoding="utf-8"?>
<Project>
  <Import Project="Avalonia.props" />

  <!-- Default Nuget consumption -->
  <ItemGroup Condition="'$(BuildAvaloniaFromSource)' != 'true'">
    <PackageReference Include="Avalonia" Version="$(AvaloniaVersion)" />
    <PackageReference Include="Avalonia.Desktop" Version="$(AvaloniaVersion)" />
  </ItemGroup>

  <!-- Build Avalonia from source -->
  <Import Condition="'$(BuildAvaloniaFromSource)' == 'true'" Project="$(AvaloniaRootFolder)\build\ReferenceCoreLibraries.props"/>
  <Import Condition="'$(BuildAvaloniaFromSource)' == 'true'" Project="$(AvaloniaRootFolder)\build\BuildTargets.targets"/>
  <Import Condition="'$(BuildAvaloniaFromSource)' == 'true'" Project="$(AvaloniaRootFolder)\build\SourceGenerators.props" />

</Project>

So, dependent on the root switch we consume either the nuget packages or the project references defined in the Avalonia props files

The .props file for apps consuming Avalonia:

<?xml version="1.0" encoding="utf-8"?>
<Project>
  <Import Project="AvaloniaLibrary.props"/>
  
  <!-- Default Nuget consumption -->
  <ItemGroup Condition="'$(BuildAvaloniaFromSource)' != 'true'">
    <PackageReference Include="Avalonia.Themes.Fluent" Version="$(AvaloniaVersion)" />
    <PackageReference Include="Avalonia.Fonts.Inter" Version="$(AvaloniaVersion)" />
    <!-- Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration. -->
    <PackageReference Condition="$(Configuration.StartsWith('Debug'))" Include="Avalonia.Diagnostics" Version="$(AvaloniaVersion)" />
  </ItemGroup>

  <!-- Build Avalonia from source -->
  <ItemGroup Condition="'$(BuildAvaloniaFromSource)' == 'true'">
    <ProjectReference Include="$(AvaloniaRootFolder)\src\Avalonia.Fonts.Inter\Avalonia.Fonts.Inter.csproj"/>
    <ProjectReference Include="$(AvaloniaRootFolder)\src\Avalonia.Themes.Fluent\Avalonia.Themes.Fluent.csproj"/>
    <ProjectReference Include="$(AvaloniaRootFolder)\src\Avalonia.Diagnostics\Avalonia.Diagnostics.csproj"/>
  </ItemGroup>
  <Import Condition="'$(BuildAvaloniaFromSource)' == 'true'" Project="$(AvaloniaRootFolder)\build\SampleApp.props"/>
  
</Project>

Note: there are some more props files for other Avalonia packages like DataGrid etc. Of course you could do a single .props if you did not want to distinguish in such detail.

This does the job for the project vs. nuget references. In order to properly build from source and set breakpoints I needed a sln file that contains the necessary Avalonia projects. This took me a while to get right for a clean build. But its seems that these assemblies are good enough to go:

Note that the project reference are done using the substituted drive letter from above:

Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Avalonia.Desktop", "A:\src\Avalonia.Desktop\Avalonia.Desktop.csproj", "{C8B5BB36-C884-49C7-AD7B-FAB16DD17A5B}"
EndProject

The way I am doing this in your mono repo, is to define one such solution with the Avalonia projects and our apps and libraries. Maintaining this solution over time will require regular changes and I only want to do that in a single solution file.

The overall sln then looks like this:

The project just imports the .props file. I also linked the .props files into the solution to allow for easier changes. You can then just normally run the app settings <BuildAvaloniaFromSource>false</BuildAvaloniaFromSource> or running it from source with true.

Please note there are of course workloads that you must install to build Avalonia. This solution is limited to desktop. So other than a specific .net SDK (7.0.404 at the time of this post) that is not so hard to do.

Hope this helps.