Analysis of the core mechanism of Handler from the perspective of source code

The "Tao" to follow when looking at the source code:

1. Follow the universal trilogy of what, how, why learning principles, from appearance to essence.
   what is what this thing is, what is it useful for, what problem does it solve, what syntax does it have, and what features does it have.
   How is how this thing solves these problems, what is the implementation mechanism, and how does it work internally.
   Why is why this thing is designed this way, why it can't be designed like that, what's the point of such a design, and what are the advantages and disadvantages.

2. If there is a design document, read the design document first, understand the design idea and the overall principle, and then look at the source code.

3. The source code is the specific implementation of the design idea, and the source code is to further understand the design idea from a practical point of view.

4. It is almost meaningless to directly look at the source code without understanding the design ideas and overall principles. It will make you feel confused after entering the source code. Of course, if there is really no design document for some things, you can directly look at the source code to understand the design idea, but it may take several times the effort and time.

5. When looking at the source code, first grasp the main line, and then look at the details, that is, first master the trunk, master the skeleton context, and then look at the details.

6. A good learning method is to follow experienced people to learn the design ideas and overall principles of the framework, and then implement the core principles and core functions of the framework by hand, and then look at the details of the source code later. It may take ten days and a half months for a framework to read the design documents and source code by itself to understand the overall principle, and it may only take one or two days for an experienced person to follow.

7. Writing complex knowledge points several times and understanding the principle will be as easy as writing an if-else statement, and writing it several times is self-seeking. Of course, the premise is that you need to think and understand more when writing.

8. The first article is the basic use of the framework, the second article is the core principles and core functions of the handwritten implementation framework, and the third article is the source code analysis of the framework.

9. After reading the design document ten times, it is not as profound as you can draw the relevant design documents, class diagrams, sequence diagrams, etc. manually. After reading the code ten times, it is not as deep as the understanding you can get by handwriting the code once. In the process, you are actively output, you will actively think, rather than passive input.

10. When writing a summary of an article, write a summary according to your own ideas.

11. When writing code, experienced developers will not only complete the development tasks from the perspective of business requirements, but also optimize the code from the perspectives of CPU, memory, operating system, data structures and algorithms, and network optimization.

First understand the design idea, understand the basic knowledge, and then look at the code. The code is the concrete realization of the idea. When you read the source code, you will only get confused.
Don't look at everything when looking at the code, just look at the mainline code (the main thing is to understand its ideas, not the code details, the code details are to better understand the specific implementation of its ideas), the mainline code logic mastered and then selective See code for details.

You have to know what to study and to what extent, otherwise, you will be like a headless flies, and in the end, you will be good at everything and not perfect at everything.

Plan the route
in the early stage: 1. Enter the big factory early, and rate it (need to train the skills first)
2. Start a business (need to train the skills first)
3. Change careers

Be sure to define the boundaries, don't learn everything, do everything. APP development involves: Java foundation, UI, four major components, performance optimization, NDK, open source framework, architecture, data structure and algorithm, design pattern, etc. If you do APP development, you need to find a way to do APP development well. Don't think about the security direction of APP, it seems to make money, reverse engineering seems to make money, audio and video seems to make money, and game development seems to make money... Do I want it? Turn around... Don't think about in-depth study of Linux system development, I feel that in-depth study of Linux seems to be very awesome (Linux system is very large, usually a team composed of a very large number of people cooperates in development, and each person specializes in One of the modules. Including framework development, a single person may only be responsible for a small part of it, such as only responsible for AMS, WMS, PMS-related parts.) ... In fact, people are envious of you to make a beautiful APP ... Correct The thinking is: to do APP development, we need to find a way to do APP development well. We need to be sophisticated. What a society with a high degree of division of labor needs is professionalism . Human energy is limited. Only by doing a good job in one direction can you be diligent and professional.

Well, let's enter the main topic of this article.

Objectives of this article:
1. Three main lines of Handler source code analysis
2. Technologies involved in source code that cannot be ignored
3. Handler related interview questions

Reference: The
Android development boss takes a comprehensive interpretation of the core mechanism of Handler from the perspective of source code, and calmly faces the Handler interview questions
. Are you always asked Handler? Take you to interpret the core mechanism of Handler from the perspective of source code