C + + design pattern shallow observer pattern

Observer Mode (OBSERVER): Defines a one-to-many dependency that allows multiple observer objects to listen to a principal object at the same time. This subject object notifies all observer objects when the state changes, enabling them to automatically update themselves.

Pattern implementation:

[code]//Observer abstract base class class observer{public:virtual void Update (int) = 0;};/  /subject, Target class subject{public:virtual void Attach (Observer *) = 0; Value virtual void Detach (Observer *) = 0; Out of virtual void Notify () = 0;   Notice};class concreateobserver:public observer{private:subject *m_psubject; 1. The specific observer, maintains a reference to the ConcreteSubject object 2. Stores the state, which should be consistent with the state of the target public://3. Implements the update interface of the observer to keep its state and the state of the target To Concreateobserver (Subject *psubject): M_psubject (psubject) {} void Update (int value) {std::cout << "Co Ncreateobserver get the update.    New state: "<< value << Std::endl; }};class concreateobserver2:public observer{private:subject *m_psubject;public:concreateobserver2 (Subject *pSubje CT): M_psubject (psubject) {} void Update (int value) {std::cout << ConcreateObserver2 get the update.    New state: "<< value << Std::endl; }};//1. The status is deposited into each Concreateobserver object//2. When its state changes, it notifies its various observers of class CONCREATESUBJEct:public subject{private:std::list<observer *> m_observerlist;    int m_istate;public:void Attach (Observer *pobserver);    void Detach (Observer *pobserver);    void Notify ();    void setState (int state) {m_istate = state; }};void Concreatesubject::attach (Observer *pobserver) {m_observerlist.push_back (pobserver);} void Concreatesubject::D etach (Observer *pobserver) {m_observerlist.remove (pobserver);}    void Concreatesubject::notify () {std::list<observer *>::iterator it = M_observerlist.begin ();        while (It! = M_observerlist.end ()) {(*it)->update (m_istate);    ++it; }}

Client:

[Code]int Main () {    //create Subject    concreatesubject *psubject = new Concreatesubject ();    Create Observer    Observer *pobserver = new Concreateobserver (psubject);    Observer *pobserver2 = new ConcreateObserver2 (psubject);    Change of the State    psubject->setstate (2);    Register The Observer    Psubject->attach (Pobserver);    Psubject->attach (pObserver2);    Psubject->notify ();  Output:concreateobserver get the update. New state:2                                  //concreateobserver2 get the update. New State:2    //unregister The Observer    Psubject->detach (Pobserver);    Psubject->setstate (3);    Psubject->notify ();  Output:concreateobserver2 get the update. New state:3    Delete pobserver;    Delete PObserver2;    Delete Psubject;}

The above is the C + + design mode of shallow knowledge of the content of the observer mode, more relevant content please pay attention to topic.alibabacloud.com (www.php.cn)!

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