Dave's Box

Binding private and internal members using the CompositionContainer

By default, the CompositionContainer will not bind to private and internal members. For example, given the following fictional class:

public class ConnectionFactory
{
    [Import("ConnectionString")]
    private string _ConnectionString;

    public string ConnectionString
    {
        get { return _ConnectionString; }
    }

    [...]
}

Running the following code:

CompositionContainer container = new CompositionContainer();

container.AddValue("ConnectionString", "Data Source=.;Initial Catalog=Northwind;Integrated Security=True");

ConnectionFactory factory = new ConnectionFactory();
container.AddComponent(factory);
container.Bind();

Console.WriteLine("ConnectionString: " + factory.ConnectionString);

Outputs the following:

ConnectionString: 

As you can see, the value we added explicitly to the container was never bound to the ConnectionFactory._ConnectionString field.

To allow private and internals members to be injected, simply apply the AllowNonPublicCompositionAttribute to the assembly that contains the imports. For example:

[assembly: AllowNonPublicComposition]

Rerunning the above code after applying the attribute, outputs the following:

ConnectionString: Data Source=.;Initial Catalog=Northwind;Integrated Security=True

Note: This applies to both private and internal imports and exports.