MEF Instantiate composition only once during application startup

Question

We can instantiate MEF composition using following code:

private void Compose()
{
    DirectoryCatalog catalog = new DirectoryCatalog(System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin"), "*.dll");
    CompositionContainer container = new CompositionContainer(catalog);
    container.SatisfyImportsOnce(this);
}

This works absolutely fine. But need to be instantiated in the constructor of each class wanting composition.

How can I instantiate the same only once when the web application loads and it works fine for all imports within the entire web application.

Thanks

Answer 1

You can write a static helper class that will encapsulate your container and will lazily initialize it on first-time use, and return already instantiated container on following uses. Something like this:

public static class CompositionUtil
{
    private static readonly Lazy<CompositionContainer> _container = new Lazy<CompositionContainer>(InitContainer);

    private static CompositionContainer InitContainer()
    {
        DirectoryCatalog catalog = new DirectoryCatalog(System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "bin"), "*.dll");
        return new CompositionContainer(catalog);
    }

    public static CompositionContainer Container
    {
        get { return _container.Value; }
    }
}

and it's usage will look like simply

CompositionUtil.Container.SatisfyImports(this);