Autofac Property Injection and Method Injection

Posted 2020-10-31 lenmom

While constructor parameter injection is the preferred method of passing values to a component being constructed, you can also use property or method injection to provide values.

Property injection uses writeable properties rather than constructor parameters to perform injection. Method injection sets dependencies by calling a method.

Property Injection

If the component is a lambda expression component, use an object initializer:

builder.Register(c => new A { B = c.Resolve<B>() });

To support circular dependencies, use an activated event handler:

builder.Register(c => new A()).OnActivated(e => e.Instance.B = e.Context.Resolve<B>());

If the component is a reflection component, use the PropertiesAutowired() modifier to inject properties:

builder.RegisterType<A>().PropertiesAutowired();

If you have one specific property and value to wire up, you can use the WithProperty() modifier:

builder.RegisterType<A>().WithProperty("PropertyName", propertyValue);

Method Injection

The simplest way to call a method to set a value on a component is to use a lambda expression component and handle the method call right in the activator:

builder.Register(c => {
  var result = new MyObjectType();
  var dep = c.Resolve<TheDependency>();
  result.SetTheDependency(dep);
  return result;
});

If you can’t use a registration lambda, you can add an activating event handler:

builder
  .Register<MyObjectType>()
  .OnActivating(e => {
    var dep = e.Context.Resolve<TheDependency>();
    e.Instance.SetTheDependency(dep);
  });