Difference between Observer Mode and Publish-Subscribe Mode

The observer pattern defines a one-to-many dependency between objects. When the state of an object changes, all the objects that depend on it will be notified and updated automatically. Observer mode belongs to behavior mode, which focuses on the communication between objects. Observer mode is the communication between observer and observed. Observer mode has another name "publish-subscribe mode" or "subscribe-publish mode". Subscribers and subscription targets are linked together. When the subscription target changes, subscribers will be notified one by one.

2 cases

3 Main problems to be solved

When notifying other objects of an object's state change, we should consider ease of use and low coupling to ensure a high degree of cooperation.

Four advantages

Five shortcomings

1 Introduction

In fact, there is no publish-subscribe mode among the 24 basic design patterns. As mentioned above, it is just another name for the observer mode. But after the precipitation of time, it seems that he has become powerful, independent of the observer mode and has become a different design mode. In the current publish-subscribe mode, the message sender called publisher will not send the message directly to the subscriber, that is to say, the publisher and subscriber do not know each other's existence. There is a third component between publisher and subscriber, called message broker or dispatch center or middleware, which maintains the connection between publisher and subscriber, filters all incoming messages from publisher and distributes them to subscribers accordingly.

2 cases

Three advantages

Four shortcomings

5 mainly solve problems

Publish-subscribe pattern is a common front-end design pattern, which is widely used in mainstream MVVM framework. Its main functions are as follows:

The front-end event binding has three elements:

On the surface:

A deeper layer:

From the use level.