Android Asynchronous Communication: Graphical and Text Detailed Explanation of the Working Principle of the Handler Mechanism

foreword

• In the Androiddevelopment of multi-threaded application scenarios , the Handlermechanism is very common

• Today, I will explain in detail how the Handlermechanism works, I hope you will like it

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content

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1. Definitions

A set of Androidmessage passing mechanisms

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2. Function

In a multi-threaded application scenario, the operation information that needs to be updated in the worker thread is UIpassed to the UImain thread , so as to realize UIthe update processing of the pair of worker threads, and finally realize the processing of asynchronous messages.

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3. Why use the Handlermessage passing mechanism

• Answer: Multiple threads update the UI concurrently while ensuring thread safety
• The specific description is as follows

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4. Related concepts

HandlerThe related concepts in the mechanism are as follows:

In the following explanation, I will directly use the English name to explain, namely Handler, Message, Message Queue, Looper, I hope you are familiar with the relevant concepts first

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5. Analysis of the working principle

Below, I will qualitatively explain Handlerthe workflow of the mechanism

5.1 Workflow Analysis

HandlerThe workflow of the mechanism mainly includes 4 steps:
1. Asynchronous communication preparation
2. Message sending
3. Message loop
4. Message processing

The details are as follows:

5.2 Workflow diagram

5.3 Schematic

5.4 Special attention

The correspondence between threads （Thread）, loopers, （Looper）and handlers is as follows:（Handler）

• 1 thread （Thread）can only bind 1 looper （Looper）, but can have multiple handlers（Handler）
• 1 looper （Looper）can bind multiple handlers（Handler）
• 1 handler can （Handler）only bind 1 1 circulator（Looper）

So far, Handlerthe working principle of the asynchronous message passing mechanism has been explained.

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6. Summary

• This article Handlerprovides a comprehensive explanation of how the mechanism works
• Next, I will continue to explain Androidin theHandler relevant knowledge of the asynchronous communication transfer mechanism in

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