XML Configuration

Most IoC containers provide a programmatic interface as well as XML configuration support, and Autofac is no exception.

Autofac encourages programmatic configuration through the ContainerBuilder class. Using the programmatic interface is central to the design of the container. XML is recommended when concrete classes cannot be chosen or configured at compile-time.

Before diving too deeply into XML configuration, be sure to read Modules - this explains how to handle more complex scenarios than the basic XML component registration will allow.

Syntax

Autofac can read standard .NET application config files. These are the ones called app.config.

You need to declare a section handler somewhere near the top of your config file:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <section name="autofac" type="Autofac.Configuration.SectionHandler, Autofac.Configuration"/>
    </configSections>

Then, provide a section describing your components:

<autofac defaultAssembly="Autofac.Example.Calculator.Api">
    <components>
        <component
            type="Autofac.Example.Calculator.Addition.Add, Autofac.Example.Calculator.Addition"
            service="Autofac.Example.Calculator.Api.IOperation" />

        <component
            type="Autofac.Example.Calculator.Division.Divide, Autofac.Example.Calculator.Division"
            service="Autofac.Example.Calculator.Api.IOperation" >
            <parameters>
                <parameter name="places" value="4" />
            </parameters>
        </component>

The defaultAssembly attribute is optional, allowing namespace-qualified rather than fully-qualified type names to be used. This can save some clutter and typing, especially if you use one configuration file per assembly (see Additional Config Files below.)

Valid ‘component’ Attributes

The following can be used as attributes on the component element (defaults are the same as for the programmatic API):

Attribute Name	Description	Valid Values
type	The only required attribute. The concrete class of the component (assembly-qualified if in an assembly other than the default.)	Any .NET type name that can be created through reflection.
service	A service exposed by the component. For more than one service, use the nested services element.	As for type.
instance-scope	Instance scope - see Instance Scope.	per-dependency, single-instance or per-lifetime-scope
instance-ownership	Container’s ownership over the instances - see the InstanceOwnership enumeration.	lifetime-scope or external
name	A string name for the component.	Any non-empty string value.
inject-properties	Enable property (setter) injection for the component.	yes, no.

Valid ‘component’ Nested Elements

Element	Description
services	A list of service elements, whose element content contains the names of types exposed as services by the component (see the service attribute.)
parameters	A list of explicit constructor parameters to set on the instances (see example above.)
properties	A list of explicit property values to set (syntax as for parameters.)
metadata	A list of item nodes with name, value and type attributes.

There are some features missing from the XML configuration syntax that are available through the programmatic API - for example registration of generics. Using modules is recommended in these cases.

Modules

Configuring the container using components is very fine-grained and can get verbose quickly. Autofac has support for packaging components into Modules in order to encapsulate implementation while providing flexible configuration.

Modules are registered by type:

<modules>
    <module type="MyModule" />

You can add nested parameters and properties to a module registration in the same manner as for components above.

Additional Config Files

You can include additional config files using:

<files>
    <file name="Controllers.config" section="controllers" />

Configuring the Container

First, you must reference Autofac.Configuration.dll in from your project.

To configure the container use a ConfigurationSettingsReader initialised with the name you gave to your XML configuration section:

var builder = new ContainerBuilder();
builder.RegisterModule(new ConfigurationSettingsReader("mycomponents"));
// Register other components and call Build() to create the container.

The container settings reader will override default components already registered; you can write your application so that it will run with sensible defaults and then override only those component registrations necessary for a particular deployment.

Multiple Files or Sections

You can use multiple settings readers in the same container, to read different sections or even different config files if the filename is supplied to the ConfigurationSettingsReader constructor.