Solution for Avalonia not running after AOT compilation

Problem Discovery#

Recently, while developing an Avalonia application, I found it was running fine during debugging but could not run after publishing, which felt strange. My publish configuration had the following two entries:

    <PublishTrimmed>True</PublishTrimmed>
    <PublishAot Condition="'$(Configuration)' != 'Debug'">true</PublishAot>

The first entry enabled trimming, and the second entry enabled AOT compilation (but it was not enabled during development because the preview window does not support AOT).

After some investigation, I discovered that both had issues:

Reflection is not friendly to AOT; my ViewLocator.cs used reflection to create objects.
Some libraries do not support trimming well, so trimming needs to be disabled for them.

Solution#

Issue 1: Eliminate Reflection#

The original code used reflection to create objects:

public Control? Build(object? param)
{
    if (param != null && param is ViewModelBase)
    {
        var viewModelType = param.GetType();
        if (_viewModelViewMappings.TryGetValue(viewModelType, out var viewType))
        {
            return (Control)Activator.CreateInstance(viewType)!; // Reflection is used here
        }
        return new TextBlock { Text = "Not Found: " + viewModelType.FullName };
    }
    return null;
}

After modification, it uses a factory method:

public Control? Build(object? param)
{
    if (param != null && param is ViewModelBase)
    {
        var viewModelType = param.GetType();
        if (_viewModelViewMappings.TryGetValue(viewModelType, out var viewFactory))
        {
            return viewFactory(); // Factory method is used
        }
        return new TextBlock { Text = "Not Found: " + viewModelType.FullName };
    }
    return null;
}

This eliminates reflection.

Issue 2: Disable Trimming for Specific Libraries#

During publishing, I noticed many trimming warnings like this:

2>Assembly 'Serilog' produced trim warnings. For more information see https://aka.ms/dotnet-illink/libraries
2>Assembly 'ReactiveUI' produced trim warnings. For more information see https://aka.ms/dotnet-illink/libraries
2>Assembly 'SukiUI' produced trim warnings. For more information see https://aka.ms/dotnet-illink/libraries
2>Assembly 'Avalonia.Controls.DataGrid' produced trim warnings. For more information see https://aka.ms/dotnet-illink/libraries
2>Assembly 'Avalonia.Controls.DataGrid' produced AOT analysis warnings.

Therefore, I modified the project's sln file to add the following snippet to limit trimming through an external XML file:

  <ItemGroup>
    <TrimmerRootDescriptor Include="TrimmerRoots.xml" />
  </ItemGroup>

Below is the content of TrimmerRoots.xml:

<?xml version="1.0" encoding="utf-8" ?>
<linker>
  <assembly fullname="Serilog" />
  <assembly fullname="Serilog.Sinks.Console" />
  <assembly fullname="Serilog.Sinks.File" />
  <assembly fullname="ReactiveUI" />
  <assembly fullname="SukiUI" />
  <assembly fullname="Serilog.Sinks.File" />
</linker>

I added all the projects that had warnings to this list. Although there were still new warnings during the subsequent compilation, the program could run normally. Thus, all issues were resolved.