Introduction
ComponentModel construction contributors are objects that implement
IContributeComponentModelConstruction interface. As their name implies they construct the
ComponentModel into its final state right after it was created.
Don't modify ComponentModel outside of contributors
It is discouraged to modify component model elsewhere than in construction contributors. After
ComponentModel is processed by its construction contributors it should be considered read only. Modifying it at any later point may lead to concurrency issues and other kinds of hard to track down issues.
The IContributeComponentModelConstruction interface
ComponentModel construction contributors are required to implement single method:
void ProcessModel(IKernel kernel, ComponentModel model);
Based on the information provided by other contributors, kernel, model's configuration or its own state they either inspect or modify the
model parameter. Windsor uses several of built in contributors itself to set up things like proxying, parameters, lifestyles, lifecycle steps, dependencies etc.
Writing your own
Writing custom contributor is one of the most common ways of extending/customizing Windsor. For the sake of example let's say we want to make all properties of type
ILogger on all components to be mandatory (By default property dependencies are optional in Windsor). To do that we could write a contributor that looks like the following:
public class RequireLoggerProperties : IContributeComponentModelConstruction
{
public void ProcessModel(IKernel kernel, ComponentModel model)
{
model.Properties
.Where(p => p.Dependency.TargetType == typeof(ILogger))
.All(p => p.Dependency.IsOptional = false);
}
}
The contributor scans all property dependencies of each component, trying to find ones that have type
ILogger and marks them as mandatory.
Plugging the contributor in
When you create your contributor you need to add it to the collection of contributors on container's
ComponentModelBuilder:
container.Kernel.ComponentModelBuilder.AddContributor(new RequireLoggerProperties ());
External resources
Blogpost by Mark Seemann (Apr 26, 2010)Blogpost by Ayende (Mar 11, 2007)