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I am trying to use Autofac and register the below class which receives one of the parameter as optional parameter (or rather null). My classes are:

class BaseSpanRecord : ISpanRecord
{
    public BaseSpanRecord(RecordType recordType, List<SpanRecordAttribute> properties)
    {
        RecordType = recordType;
        Properties = properties;
    }
}

Here RecordType is an enum and SpanRecordAttribute is a class with only properties for which i don't want to create any interface.

In the constructor RecordType and Properties are the two public properties of the interface ISpanRecord This class can be instantiated in the following ways in different places in the program:

ISpanRecord spanFileRecord = new BaseSpanRecord(recordType, null);

or

ISpanRecord spanFileRecord = new BaseSpanRecord(recordType, recordAttributeList);

How should i try to register this in the Autofac container so that it can handle the above two cases? Or should i change something in the way BaseSpanRecord class has been written to make its registration easier?

Darsin
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  • I tried using the following: `builder.RegisterType().UsingConstructor(typeof(RecordType), typeof(List)).As().InstancePerDependency();` But then it does not work for the first case. – Darsin Nov 07 '12 at 17:12

1 Answers1

2

When using a TypeParameter to resolve the instance as long as you provide the type information null should be fine. You should not need to use the UsingConstructor method on your registration.

Creating TypedParameter instances directly:

var recordTypeParam = new TypedParameter(typeof(RecordType), RecordType.Something);
var propertiesParam = new TypedParameter(typeof(List<SpanRecordAttribute>), null);
var record = container.Resolve<ISpanRecord>(recordTypeParam, propertiesParam);

Using the TypedParameter.From helper method:

var record = container.Resolve<ISpanRecord>(TypedParameter.From(RecordType.Something), TypedParameter.From((List<SpanRecordAttribute>)null));

Notice that the null was cast to List<SpanRecordAttribute> to allow for type inference with the helper method.

Alex Meyer-Gleaves
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  • Thanks @Alex. It solved my problem. But now couple of questions follow. When should i use `UsingConstructor()` or `WithParameter()` or `builder.Register(c=> new ClassA(c.Resolve()))` when autofac can resolve the constructor parameters without them being specified while registering. Pardon my knowledge of Autofac as i was unable to understand much of what was written in the Autofac wiki. I am looking for possible scenarios for the same. If you can provide any link or book, etc. then it would be really helpful. – Darsin Nov 08 '12 at 13:58