ServiceComposer.AspNetCore

Customizing ViewModel Composition options from dependent assemblies

Assemblies containing types participating in the composition process can customize the current application ViewModelCompositionOptions by defining a type that implements the IViewModelCompositionOptionsCustomization interface. At runtime, when the application starts, types implementing the IViewModelCompositionOptionsCustomization will be instantiated and the Customize method will be invoked.

[!NOTE] Types implementing IViewModelCompositionOptionsCustomization are not managed by IoC container. Dependency injection is not available.

This pattern lets a library or plugin assembly apply its own composition configuration without requiring changes to the host application’s startup code:

// In a class library assembly (e.g. Sales.ViewModelComposition.dll)
public class SalesCompositionOptionsCustomization : IViewModelCompositionOptionsCustomization
{
    public void Customize(ViewModelCompositionOptions options)
    {
        options.AssemblyScanner.AddAssemblyFilter(name =>
            name.StartsWith("Sales.")
                ? AssemblyScanner.FilterResults.Include
                : AssemblyScanner.FilterResults.Exclude);
    }
}

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When the host application calls builder.Services.AddViewModelComposition(), ServiceComposer scans loaded assemblies and automatically discovers and invokes all IViewModelCompositionOptionsCustomization implementations.

Accessing configuration

ViewModelCompositionOptions offers the ability to access the application IConfiguration instance. By default, the ViewModelCompositionOptions.Configuration property is null — accessing it throws an ArgumentException. To enable configuration support, pass the IConfiguration instance when configuring ServiceComposer:

var builder = WebApplication.CreateBuilder();
builder.Services.AddViewModelComposition(builder.Configuration);

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With that, a customization class can read configuration values:

public class SalesCompositionOptionsCustomizationWithConfig : IViewModelCompositionOptionsCustomization
{
    public void Customize(ViewModelCompositionOptions options)
    {
        var section = options.Configuration.GetSection("Sales:Composition");
        // use section values to conditionally configure options
    }
}

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