In complex software systems, we often encounter a scenario where when the state of an object changes, other objects need to be notified so that they can react accordingly. If dependencies are established directly between these objects, the coupling of the system will increase significantly and the code will become difficult to maintain. The Observer Pattern helps us solve this problem elegantly through the publish-subscribe method. This article will introduce the concept of the Observer Pattern, the difference between it and other similar patterns, and how to solve it.