Understanding the singleton pattern

  • Definition:
    • There’s only one instance
    • Global access
  • Main solutions:
    • A globally used class that is frequently created and destroyed
    • When to use:
    • When you want to control the number of instances, save systematic resource release
  • How to achieve:
    • Check whether the system already has this singleton. If so, return it. If not, create it

Advantages of the singleton pattern:

  • Having only one instance in memory reduces memory overhead, especially frequent creation and destruction
  • Usage Scenarios:
  • Global cache
  • Popup window

Definition of policy patterns

  • Define a set of algorithms, encapsulate them, and interchangeable them
  • Core:
    • Separate the use of algorithms from the implementation of algorithms

Publish and subscribe model

  • Start by figuring out who the publisher is
  • Then add a cache list to the publisher to hold callback functions to notify subscribers
  • Finally, a message is published, and the publisher iterates through the cache list, triggering the deposited subscriber callback in turn