c# - Difference between Import and ImportingConstructor attributes in MEF with proper examples? -


can me import , importingconstructor attributes in mef relevant examples , when use ? use of [import(allowdefault = true)] ?

from understanding of mef:

export attribute defined on class of type t t interface , create instance of class import attribute should defined on reference variable below

[export(typeof(icalculator))] class mysimplecalculator : icalculator {      // implement interface }  class mymainclass {    // mef engine creates instance export attribute defined    // on mysimplecalculator      [import(typeof(icalculator))]     public icalculator calculator; }

if multiple exports of type t defined in given assembly can use importmany attribute.

so can explain when use import , importingconstructor , allowdefault attribute in constructor ?

it great if can explain better examples.

any appreciated. thanks

importingconstructor

the way import/export parts in sample code, if mymainclass getting composed, implicit parameterless constructor called, then instance of mysimplecalculator assigned calculator field.

now let's rather want have readonly field/a get-only property, or otherwise need access icalculator in constructor, need have passed constructor rather later on assigned field:

public interface icalculator {     bool quack { get; } }  [export(typeof(icalculator))] public class mysimplecalculator : icalculator {     public bool quack => true; }  [export] public class mymainclass {     public icalculator calculator { get; }     public string blah { get; }      [importingconstructor]     public mymainclass(icalculator calculator)     {         calculator = calculator; // assign readonly property         blah = calculator.quack ? "foo" : "bar"; // based on calculator     } }

now argument(s) constructor implicitly imported , satisfied corresponding export.

allowdefault

if [import] something, must available or composition fails.

if [import(allowdefault = true)] something, composition wont' fail if there's no corresponding export, null/false/0 imported value.

btw: sorry being sarcastic, answer rtfm.


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