Notes - Chang Geng

part one

There are two other things that really drive computers to form their own engineering systems ：

• People's ability hasn't become stronger , At least not stronger at the same level .
• Man will make the best of everything

Because people don't have the ability “ keep pace with ” machine , That's why there are all kinds of models 、 Method 、 Tools and so on to make up for people's shortcomings , To maximize machine performance . It's like a sentence I suddenly thought of when flash memory was boring the other day ：  Structure is a compromise of objective deficiency , Norm is a compromise of subjective deficiency .

When we need machines to do more , We can't do everything on one chip , That's why there's a von Neumann model 、 Computer architecture , It can't be solved by one machine , That's why we need the Internet 、 Distributed 、 Cloud computing .

Again , With the development of computers , There's so much to do , So there's the concept of software . When “ Development ” Formalization , The software we need becomes ： Functional complexity 、 Management unification 、 Multiple entrance .

What really changes is not the objective nature , It is demand. . Like I said here “ Software entrance ” Objectively, we have only one , In principle, there is only one startup program 、 A snippet of startup code . but “ Software entry ”, Has been referred to from Main Function becomes the beginning of reference UI, Users have changed from referring to professionals to referring to general consumers , Software requirements first , The definition of software , And demand is changing .

A software needs several orders of magnitude more code than at that time ：

• Objectively, we can't make a display that can show all the codes
• Subjectively, we can't see all the code in super fast scrolling

So we need to add indexes 、 Organize code with multiple files .

The development of machines and the demand expansion and refinement of software , We're starting to have a user interface （User Interface） The most suitable language for interface —— Markup language （Markup Language）. Of course ,ML Not for UI Born , It's just perfect UI, That's why UI Fall in love .

Because it's higher UI The needs of , That's why the code is officially divided into descriptions of what to do （ Business logic ） And what （UI） The two part , Because we can't work in two ways of thinking at the same time , The human brain in development is single threaded . What we see is going on at the same time UI And logic development is just that we learned to switch quickly in two modes , Looks like it's going on at the same time , Not really at the same time . The same thing happens in the development of different pieces of code .

part two

When demand becomes huge , The solution is going to be huge ; When the solution becomes large , There will be subdivisions ; When subdivision occurs , There will be questions about how to manage it .

Software has evolved from dealing with one transaction to dealing with many transactions , Among all affairs 、 The order 、 The relationship between primary and secondary , It's getting more and more complicated . Because data and logic are huge , So data and logic are separated , And then the event and the business are separated .

Their relationship has continued to develop before we can make it clear, and it has become more difficult to make it clear , But at one point in time , they UI And the field is roughly divided into these atoms ：

• Interface
• data
• event
• Business

If you want to elaborate, there will be more complicated details , But I believe it's less controversial .

When a problem comes up once, it's a problem , When a problem occurs countless times, it becomes history , When a problem will occur many times , It will require a clear definition and solution .

among , The problem of data updating and interface updating has been magnified countless times , Because it's happened countless times .

MVC The general process of ：View（ Interface ） Triggering event -->Controller（ Business ） Handled the business , And then triggered a data update --> I don't know who updated it Model The data of -->Model（ With data ） Back to View-->View Update data

Yes MVC The idea of improvement is the same ： Severed View and Model The connection of , Give Way View And the only Presenter（ primary Controller） Interaction , Reduce the number of objects that need to be maintained during demand changes .

This way suits our expectation , Because we tend to ：

• Solve problems at a lower cost
• Solve problems in a more understandable way

Many times it's not a bad model , It's because people can't do it , For example, it's not easy to understand , We will choose an easy to understand way . Computers rely on Moore's law to solve problems with increasing numbers , And people solve problems by changing their ways . Also because of objective reasons, we are not good at maintaining the relationship between multiple objects , So we changed , Or simplified this way .

MVP Defined Presenter and View Interface between , Some can be independently developed according to the existing interface protocol , So as to solve the problem of frequent change of interface requirements . There are interfaces in the above two figures , However, the implementation and use details of the interface are different , But it's the same in mind .

What I want to mention here is , in fact , The most frequent demand change is not necessarily the closest user interface , But it's almost certain , The interface closest to the user is the one that needs to be changed most frequently due to changes in requirements . Of course , If View If it is API instead of UI, Let's say something else .

ViewModel Basically MVP Of Presenter and MVC Of Controller 了 , and View and ViewModel There is no room. MVP Interface of , It's direct interaction , Using data “ binding ” Data update events do not require developers to manually write special use cases , It's automatic two-way synchronization . You can think of data binding as Observer Pattern or Publish/Subscribe Pattern , The principle is to Using a unified and centralized way to realize frequent data updating .

Compared with MVP,MVVM Not only simplifies the dependency between business and interface , It also optimizes the solution of frequent data update , It even provides an effective solution mode .

                                  ------  Excerpt from 《 from Script To Code Blocks、Code Behind To MVC、MVP、MVVM》