C # Object-oriented design-observer mode (17)

First, preface

The observer pattern is also called the Publish-subscribe pattern.
The Observer pattern defines a one-to-many dependency that allows multiple observer objects to listen to a Subject object at the same time, and notifies all observer objects when the state of the subject is changed, so that they can automatically update themselves.

When do I use observer mode?
When a change to an object needs to change other objects at the same time.

Second, the structure diagram

Third, instance code

usingSystem;usingSystem.Collections.Generic;usingSystem.Text;namespaceObserver Pattern {classProgram {Static voidMain (string[] args) {            //boss amBoss Huhansan =NewBoss (); //colleagues who look at sharesStockobserver Tongshi1 =NewStockobserver ("Li Zhe", Huhansan); //look at the NBA colleagues.Nbaobserver Tongshi2 =NewNbaobserver ("Li Ming", Huhansan); Huhansan.            Attach (TONGSHI1); Huhansan.            Attach (TONGSHI2); Huhansan.            Detach (TONGSHI1); //boss BackHuhansan. Subjectstate ="I huhan back! "; //Send a notificationHuhansan.            Notify ();        Console.read (); }    }    //Notifier Interface    InterfaceSubject {voidAttach (Observer Observer); voidDetach (Observer Observer); voidNotify (); stringSubjectstate {Get; Set; }    }    classSecretary:subject {//Colleagues List        PrivateIlist<observer> observers =NewList<observer>(); Private stringAction; //Increase         Public voidAttach (Observer Observer) {observers.        ADD (Observer); }        //reduced         Public voidDetach (Observer Observer) {observers.        REMOVE (Observer); }        //Notice         Public voidNotify () {foreach(Observer oinchobservers) O.update (); }        //Foreground Status         Public stringSubjectstate {Get{returnAction;} Set{action =value;} }    }    classBoss:subject {//Colleagues List        PrivateIlist<observer> observers =NewList<observer>(); Private stringAction; //Increase         Public voidAttach (Observer Observer) {observers.        ADD (Observer); }        //reduced         Public voidDetach (Observer Observer) {observers.        REMOVE (Observer); }        //Notice         Public voidNotify () {foreach(Observer oinchobservers) O.update (); }        //Boss Status         Public stringSubjectstate {Get{returnAction;} Set{action =value;} }    }    //Abstract Viewer    Abstract classObserver {protected stringname; protectedSubject Sub;  PublicObserver (stringname, Subject sub) {             This. Name =name;  This. Sub =Sub; }         Public Abstract voidUpdate (); }    //colleagues who look at shares    classStockobserver:observer { PublicStockobserver (stringname, Subject sub):Base(name, sub) {} Public Override voidUpdate () {Console.WriteLine ("{0} {1} Close stock Quotes and continue working! ", Sub.        Subjectstate, name); }    }    //look at the NBA colleagues.    classNbaobserver:observer { PublicNbaobserver (stringname, Subject sub):Base(name, sub) {} Public Override voidUpdate () {Console.WriteLine ("{0} {1} Close the NBA Live, continue to work! ", Sub.        Subjectstate, name); }    }}

Iv. deficiencies

In the above code, the abstract notifier relies on the abstract observer, and the Observer's method is the same name as the update (), if the Observer has a different name of the method, the use of event delegates to implement abstract notifier to the abstract observer's dependence, but also do not need the observer is the general update () method.

Because abstract notifier does not want to rely on abstract observers, the "increase", "reduce" The Observer's method is also unnecessary.

usingSystem;usingSystem.Collections.Generic;usingSystem.Text;namespaceObserver Pattern {classProgram {Static voidMain (string[] args) {            //boss HuhanBoss Huhansan =NewBoss (); //colleagues who look at sharesStockobserver Tongshi1 =NewStockobserver ("Li Zhe", Huhansan); //look at the NBA colleagues.Nbaobserver Tongshi2 =NewNbaobserver ("Li Ming", Huhansan); Huhansan. Update+=NewEventHandler (tongshi1.            Closestockmarket); Huhansan. Update+=NewEventHandler (Tongshi2.            closenbadirectseeding); //boss BackHuhansan. Subjectstate ="I huhan back! "; //Send a notificationHuhansan.            Notify ();        Console.read (); }    }    //Notifier Interface    InterfaceSubject {voidNotify (); stringSubjectstate {Get; Set; }    }    //delegate for event handlers    Delegate voidEventHandler (); classSecretary:subject {//declares an event update, type is delegate EventHandler         Public EventEventHandler Update; Private stringAction;  Public voidNotify () {Update (); }         Public stringSubjectstate {Get{returnAction;} Set{action =value;} }    }    classBoss:subject {//declares an event update, type is delegate EventHandler         Public EventEventHandler Update; Private stringAction;  Public voidNotify () {Update (); }         Public stringSubjectstate {Get{returnAction;} Set{action =value;} }    }    //colleagues who look at shares    classStockobserver {Private stringname; PrivateSubject Sub;  PublicStockobserver (stringname, Subject sub) {             This. Name =name;  This. Sub =Sub; }        //Close Stock Quotes         Public voidClosestockmarket () {Console.WriteLine ("{0} {1} Close stock Quotes and continue working! ", Sub.        Subjectstate, name); }    }    //look at the NBA colleagues.    classNbaobserver {Private stringname; PrivateSubject Sub;  PublicNbaobserver (stringname, Subject sub) {             This. Name =name;  This. Sub =Sub; }        //Close NBA Live         Public voidclosenbadirectseeding () {Console.WriteLine ("{0} {1} Close the NBA Live, continue to work! ", Sub.        Subjectstate, name); }    }}

C # Object-oriented design-observer mode (17)