What is Import Attribute?

Answer:

MEF is a framework for creating extensible applications that allows developers to discover and use extensions with no configuration required.Part is an object (e.g. a class, a method or a property) that can be imported or exported to the application.In MEF parlance, Import attribute defines the need that a part has.

e.g.

[Import(typeof(ICalculator))]

public ICalculator CalciPlugin { get; set; }

The [Import] attribute declares something to be import.At runtime, the composition engine will fill it when an object is composed. The import must satisfy a contract and the Export has to match the same contract.The interface specified here is
ICalculator.Any export declared with a matching contract will fulfill this import. e.g.

[Export(typeof(ICalculator))]

    public class Add:ICalculator

    {

        #region Interface members

        public int GetNumber(int num1, int num2)

        {

            return num1 + num2;

        }

        #endregion

    }

Where the interface ICalculator is declared as under

public interface ICalculator

{

        int GetNumber(int num1, int num2);

}

Multiple values can be imported by using the [ImportMany] attribute.