Delegates（委托）delegatetype,definesaprotocol,specifyingalistofparametertypesandareturntype.delegateintTransformer(intx);//methoddeclaration???TransformeriscalledamethodcallerdelegateinstanceclassTest{

staticvoidMain()

{

Transformert=Square;//createdelegateinstance

intresult=t(3);//Invokedelegate

Console.WriteLine(result);//9

}

staticintSquare(intx){returnx*x;}//targetmethod}Transformert=Square;//createdelegateinstanceTransformert=newTransformer(Square);thestatementsaboveplaythesamerole.theformerisshorthandforthelatter.t.Invoke(3);

t(3)plug-inmethodwithdelegateswriteautilitymethodnamedTransformthatappliesatransformtoeachelementinanintegerarray.TheTransformmethodhasadelegateparameter,forspecifyingaplug-intransform.寫一個名為Transform的函數(shù)，對整型數(shù)組中的每個元素加1，利用委托作為Transform的一個形參。publicdelegateintTransformer(intx);classUtil{publicstaticvoidTransform(int[]values,Transformert){for(inti=0;i<values.Length;i++)values[i]=t(values[i]);}}classTest{staticvoidMain(){int[]values={1,2,3};Util.Transform(values,Square);foreach(intiinvalues)Console.Write(i+"");//149}

staticintSquare(intx){returnx*x;}}MulticastDelegates

多播委托;組播委托;多路廣播委托Alldelegateinstanceshavemulticastcapability,meaningthatadelegateinstancecanreferencealistoftargetmethods,SomeDelegated=SomeMethod1;d+=SomeMethod2;Removeoneoftargetmethodsfromadelegateinstance:d-=SomeMethod1;Targetmethods:

InstancevsstaticmethodBothinstancemethodsandstaticmethodscanbethetargetmethodsofadelegateinstance.TheinstancetowhichtheinstancemethodbelongsisreferencedbySystem.Delegateclass’sTargetproperty.classMyClass

{publicvoidfun(intx)

{Console.WriteLine(x);

}publicoverridestringToString()

{return"MyClass";

}

}classProgram

{delegatevoidmyDelegate(intx);staticvoidMain(string[]args)

{MyClassmc=newMyClass();myDelegatedel=newmyDelegate(mc.fun);//實例函數(shù)del.Invoke(20);//20Console.WriteLine(del.Target.GetType());//example.MyClassConsole.WriteLine(del.Target.ToString());//"MyClass"

}

}GenericdelegateTypespublicdelegateTTransformer<T>(Targ);staticdoublesqr(doublex){returnx*x;}staticvoidMain(){Transformer<double>s=Square;Console.WriteLine(s(3.3));//10.89}Func&ActionDelegatesFuncandActionarebothgenericdelegates,definedintheSystemnamespace.delegateTResultFunc<outTResult>();delegateTResultFunc<inT,outTResult>(Targ);delegateTResultFunc<inT1,inT2,outTResult>(T1arg1,T2arg2);...andsoon,uptoT16delegatevoidAction();delegatevoidAction<inT>(Targ);delegatevoidAction<inT1,inT2>(T1arg1,T2arg2);...andsoon,uptoT16publicstaticvoidfun<T>(T[]values,Func<T,T>transformer)

{for(inti=0;i<values.Length;i++)

{values[i]=transformer(values[i]);Console.WriteLine(values[i]);

}

}publicstaticdoubleadd(doublex){returnx+20;}staticvoidMain(string[]args)

{double[]arr=newdouble[]{1,2,3,4,5};fun<double>(arr,add);

}publicstaticvoidfun<T>(T[]values,Action<T>transformer)

{for(inti=0;i<values.Length;i++)

{transformer(values[i]);

}

}publicstaticvoidprint(doublex){Console.WriteLine(x);}staticvoidMain(string[]args)

{double[]arr=newdouble[]{1,2,3,4,5};fun<double>(arr,print);

}DelegateCompatibilitydelegatetypesareallincompatiblewitheachother,eveniftheirsignaturesarethesame.delegatevoidD1();delegatevoidD2();D1d1=Method1;D2d2=d1;//compile-timeerrorD2d2=newD2(d1);//permitted!!covariancefordelegatereturntypesdelegateobjectObjectRetriever();

staticvoidMain(){ObjectRetrievero=newObjectRetriever(GetString);objectresult=o();Console.WriteLine(result);//hello}staticstringGetString(){return"hello";}contravarianceforparametertypesadelegatetargetmethodmayhavelessspecificparametertypesthandescribedbythedelegate,calledcontravariance.delegatevoidStringAction(strings);...staticvoidMain(){StringActionsa=newStringAction(ActOnObject);sa("hello");}staticvoidActOnObject(objecto)//objectissmallerthanstring{Console.WriteLine(o);//hello}Event—在類里面用Eventsusethepublisher-subscriber

model.Apublisher

isanobjectthatcontainsthedefinitionoftheeventandthedelegate.Apublisherclassobjectinvokestheeventanditisnotifiedtootherobjects.Asubscriber

isanobjectthatacceptstheeventandprovidesaneventhandler.Thedelegateinthepublisherclassinvokesthemethod(eventhandler)ofthesubscriberclass.publicdelegatevoidPriceChangedHandler(decimaloldPrice,decimalnewPrice);（1）publicclassStock

{//publisher事件發(fā)布者stringsymbol;decimalprice;publicStock(stringsymbol){this.symbol=symbol;}publiceventPriceChangedHandlerPriceChanged;//一種特殊的委托，事件（2）publicdecimalPrice

{get{returnprice;}set{if(price==value)return;//fireeventifinvocationlistisnotemptyif(PriceChanged!=null)

PriceChanged(price,value);//在publisher---Stock中調(diào)用（3）price=value;

}

}

}publicstaticvoidchange(decimalx,decimaly)

{Console.WriteLine(y);

}publicstaticvoidup(decimalx,decimaly)

{Console.WriteLine("up");Console.WriteLine(y);

}staticvoidMain(string[]args)

{Stockst=newStock("LIU");st.PriceChanged+=change;//訂閱事件st.PriceChanged+=up;//在此處訂閱事件st.Price=20;

}StandardEventPatternTheNetFrameworkdefinesastandardpatternforwritingevents.eventsarebasedontheEventHandlerdelegateandtheEventArgsbaseclass.publicdelegatevoidEventHandler<TEventArgs>(objectsource,TEventArgse)whereTEventArgs:EventArgs;derivefromEventArgspublicclassPriceChangedEventArgs:EventArgs

{publicreadonlydecimalLastPrice,NewPrice;publicPriceChangedEventArgs(decimallastPrice,decimalnewPrice){LastPrice=lastPrice;NewPrice=newPrice;}

}definepublisherclasspublicclassStock

{stringsymbol;decimalprice;publicStock(stringsymbol){this.symbol=symbol;}publiceventEventHandler<PriceChangedEventArgs>PriceChanged;//EventHandlerisadelegateprotectedvirtualvoidOnPriceChanged(PriceChangedEventArgse)//here,fireanevent

{if(PriceChanged!=null)PriceChanged(this,e);

}publicdecimalPrice

{get{returnprice;}set

{if(price==value)return;OnPriceChanged(newPriceChangedEventArgs(price,value));price=value;

}

}

}definesubscribersstaticvoidstock_price_changed(objectsender,PriceChangedEventArgse)

{if((e.NewPrice-e.LastPrice)/e.LastPrice>0.1M)Console.WriteLine("Alert,10%priceincrease!");

}staticvoidMain(string[]args)

{Stockst=newStock("LIU");st.Price=27.10M;Console.WriteLine("OK");st.PriceChanged+=stock_price_changed;st.Price=31.59M;

}nongenericEventHandlerdelegateThismeansthatnoadditionalinformationneedbetransmittedwithevent.publiceventEventHandlerPriceChanged;EventAccessorsAnevent’saccessors