The observer pattern of design pattern and its C + + general implementation (i)

Observer mode

Intention:

Defines a one-to-many dependency between objects, and when the state of an object changes, all objects that depend on it are notified and automatically updated.

Structure:

Advantages:

Abstract coupling between target (SUBJECT) and Observer (Observer)

Support for broadcast communications/notifications

Disadvantages:

can cause unexpected updates.

Example:

Consider such an example: Want to know the company's latest mm information? Join us mm Intelligence mail group. You only need to send us a subscription email, we will be the latest mm information to notify you in electronic form.

Now let's do it one step at a time. Obviously, the person who cares about the MM situation in the example is the Subscriber, and we use subscriber to express this category. Before defining subscriber, we first define a Mmstatus enumeration to represent the MM State:

1.enum mmstatus {dining, sleeping, Working};

Three constants are defined here to simply simulate the state of the MM. Now we can define the Subscriber class:

1.struct Subscriber
2.{
3.    virtual void action (mmstatus status) = 0;
4.    virtual ~subscriber () {}
5.};