Summary of using Redux architecture in ReactNative_javascript skills

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This article introduces a summary of the Redux architecture used in ReactNative and shares it with everyone. The details are as follows:

I have been using Redux for some time. in conclusion.

Why use Redux?

Background:

1. RN’s state (variable, subcomponents are invisible) and The design of props (immutable, visible to sub-components), when faced with large-scale projects, can easily cause state confusion due to inadvertent modification of state, and component rendering errors

2. RN uses Virtual DOM, which does not Target binding->Action is required to modify the UI properties. As long as the state changes, the component in the new state is rendered, and the data is transmitted in one direction, while MVC's design pattern has a two-way data flow.

3. RN is not easy to test. Redux provides a very convenient mock testing method.

Redux development

Development environment

1. Install Redux: 'npm install –save redux'

2. Install React Native and Redux binding libraries: npm install –save react-redux

3. Install Redux Thunk Asynchronous ActionMiddleware ：npm install –save redux-thunk

Three principles

Single data source

The state of the entire application is stored in an object tree, and the object tree exists in a unique store. The state in the store is bound to the component

State is read-only

The only way to change the state is to trigger the action. action is an ordinary JS object containing a type attribute, which can represent events as constants.

Use pure functions to perform modifications

Write reducers to describe how the corresponding action modifies state. Generally, you can use switch(action.type) to handle it without side effects

Use

react-redux provides connect and Provider.

1. Provider is the top-level distribution point, and its attribute is Store, which distributes State to all connected components

2. connect: accepts two parameters: one is mapStateToProps or mapDispatchToProps, one is the component itself to be bound.

Store

Store is the object that connects Reducer and action. Store has the following responsibilities:

1. Maintain the state of the application – similar to a database, storing all the state of the application.

2. Provide getState() method. Obtain all current states;

3. Provides the dispatch(action) method to update the state, which is equivalent to storing it in the database and storing the action to change the state.

4. Register the listener through subscribe(listener).

Store is essentially an object that saves the entire application's State in the form of a tree. and provides some methods. For example getState() and dispatch().

Redux application has only one Store.

Store is created through the createStore method, based on the initial State of the root Reducer of the entire application.

The code is as follows:

import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';//异步
import reducers from './reducers';
const Store = applyMiddleware(thunk)(createStore)(reducers);
export default Store;

Reducers

Action only describes the fact that something happened, and does not specify how the application is updated. state. This is what the reducer does.

The essence of Reducer is a function, and it is a pure function. There are no side effects. Simply put, the Reducer is only responsible for doing one thing, which is to modify the state in the Store based on the received action and state:

(state, action) => newState

In general implementation, switch(action.type) is used to judge different Actions, and the default is the old state. The initial state can also be defined.

Code:

import { combineReducers } from 'redux';
const newState = (state = {}, action = {}) => {
 switch (action.type) {
  case ActionTypes.CSTATE:
   return { ...state, ...action.state };
  case '_DPDATACHANGE_':
   return {...state, ...action.dpState};
  default:
   return state;
 }
};
//Reducer 合并
export default combineReducers({
 newState,
});

Note: The new state is returned. If you need to retain part of the old state value, use...state (ES7 object expansion syntax, the object will be shallow copied) Attribute, here is equivalent to Object.assign({}, state, newState)), and if you merge state, only one layer will be merged, and complex states need to be merged manually.

Action

Action is an ordinary JS object, including at least one type attribute representing the event, and other attributes can be used to pass data. In practice, a function is defined for a process. The process can include network requests and finally returns Action. This function is called Action Creator.

Code: Store can dispatch this Action. The type of action represents the identifier, and state is the data it carries.

export const newState = state => {
 Store.dispatch({
  type: ActionTypes.CSTATE,
  state,
 });
};

Persistence

When the action is triggered, the data is restored according to its reducer key, and then the action only needs to be distributed when the application starts, which is also easily abstracted into configurable Expansion services, in fact the third-party library redux-persist has done all this for us.

The code in Action can be as follows:

export const getStorage = async (key) => {
 const d = await AsyncStorage.getItem(key);
 return JSON.parse(d);
};
export const setStorage = (key, value) => {
 AsyncStorage.setItem(key, JSON.stringify(value));
};

connect

Pass-provide the getState() method. Get all current state

通过connect，绑定需要的state以及Action Creator到你的组件的props上，这样组件就可以通过props来调用Action Creator，或者根据不同props来render()不同的组件。

代码：

mapStateToProps({ newState }) {
      const value = newState[name];//name: newState.name
      return {
       name,
      };
     },

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