NgRx/Store 4和Angular5

今天看到了一篇文章关于ngrx/store的实现，感觉讲的非常详细，所以转发支持下。

@ngrx/store是基于RxJS的状态管理库。在NgRx中，状态是由一个包含action和reducer的函数的映射组成的。Reducer函数经由action的分发以及当前或初始的状态而被调用，最后由reducer返回一个不可变的状态。

Action: Action是状态的改变。它描述了某个事件的发生，但是没有指定应用的状态如何改变。

ActionReducerMap： ActionReducerMap注册了一系列的reducer，在应用中使用StoreModule对它进行配置。

ActionReducer: 它被用于创建reducer，例如logger。

MetaReducer: 在应用中使用StoreModule配置的MetaReducer构成了根的meta-reducer。

StoreModule: StoreModule是@ngrx/storeAPI中的一个模块，它被用来在应用模块中配置reducer。

createFeatureSelector: 它为状态（state）创建一个feature selector。

createSelector: 它创建一个selector用于生成一个指定的状态。

Store: 它提供了Store.select()和Store.dispatch()来与reducer协同工作。Store.select()用于选择一个selector，Store.dispatch()用于向reducer分发action的类型。

1. 使用到的技术

下面是我们的例子中用到的技术：

1. Angular 5.0.0

2. Angular CLI 1.5.0

3. NgRx/Store 4.1.1

4. TypeScript 2.4.2

5. Node.js 6.11.0

6. NPM 3.10.10

2. 安装Angular CLI和NgRX/Store

1. 确保已安装的Node和NPM的最低版本为：Node 6.9.x和NPM 3.x.x

2. 在命令行中输入以下命令：

npm install -g @angular/cli

1. 运行以下命令生成一个新的项目：

ng new my-app

1. 现在安装@ngrx/store。使用命令行进入my-app目录，然后运行如下命令：

npm i @ngrx/store --save

现在我们已经准备好使用NgRx/Store和Angular了。

3. 创建State

State是一个单独的不可变的数据结构。我们会像如下这样创建state：

export interface AppState {articleState: ArticleState;
}
export interface ArticleState {articles: Article[];
}

4. 创建Action类

NgRx的Action描述了状态的变化。对于每一个action，我们都需要创建一个继承自Action的类，同时定义其type和payload（payload是个可选参数）。

export const JAVA = 'Java';
export const  MY_ARTICLES = 'Favorite_Articles';
​
export class JavaArticlesAction implements Action {readonly type = JAVA;
}
export class FavoriteArticlesAction implements Action {readonly type = MY_ARTICLES;
​constructor(public payload: Article[]) {}
} 

5. 创建Reducer

Reducer描述了任何一个action所对应的应用的state将怎样变化。reducer创建如下：

export function reducer(state = initialState, action: fromActions.All): ArticleState {switch(action.type) {case fromActions.JAVA: {return {articles: JAVA_ARTICLES};}case fromActions.ANGULAR: {return {articles: ANGULAR_ARTICLES};} case fromActions.MY_ARTICLES: {return {articles: action.payload};}    default: {return state;}} 
} 

6. 使用createFeatureSelector和createSelector()

createFeatureSelector()被用于为任意指定的state创建一个feature selector。

export const getArticleState = createFeatureSelector<ArticleState>('articleState'); 

createSelector()使用feature selector来创建selector。

export const getArticles = createSelector(getArticleState, (state: ArticleState) => state.articles 
); 

7. 使用ActionReducerMap

ActionReducerMap注册了reducer。我们需要在我们配置我们的reducer的地方创建一个 ActionReducerMap的常量。然后在应用模块中使用StoreModule来配置这个常量。

export const reducers: ActionReducerMap<AppState> = {articleState: articleReducer.reducer
}; 

8.使用ActionReducer

ActionReducer用来创建类似logger的reducer，使用MetaReducer对它进行配置。

export function logger(reducer: ActionReducer<AppState>): ActionReducer<AppState> {return function(state: AppState, action: any): AppState {console.log('state', state);console.log('action', action);return reducer(state, action);};
} 

通过使用上面的代码，我们可以在控制台中获取每个action的状态和名称。

9.使用MetaReducer

MetaReducer由我们所创建的一系列ActionReducer所组成。在应用中使用StoreModule配置的MetaReducer构成了根meta-reducer。@ngrx/store默认使用 combineReducers在创建根meta-reducer。

export const metaReducers: MetaReducer<AppState>[] = !environment.production? [logger]: []; 

10. 使用StoreModule

StoreModule是@ngrx/storeAPI中的一个模块，它被用来在应用模块中配置reducer。

@NgModule({imports: [     ---StoreModule.forRoot(reducers, {metaReducers})]---
}) 

11. 使用Store.select()和Store.dispatch()

Store.select()和 Store.dispatch()与是reducer配合使用的。Store.select()用于选择一个selector，Store.dispatch()用于向reducer分发action的类型。 要使用Store, 在组件中创建一个Observable类型的属性。

articles: Observable<Article[]> 

现在使用依赖注入来实例化Store，然后选择一个selector。

constructor(private store: Store<ArticleState>) {this.articles = store.select(articleReducer.getArticles);
} 

现在分发这个action以通过reducer改变state。

showJavaArticles(){this.store.dispatch(new fromActions.JavaArticlesAction());
} 

12. 完整的例子

下面是我们的例子的项目结构：

my-app
|
|--src
|   |
|   |--app 
|   |   |
|   |   |--actions
|   |   |    |
|   |   |    |--article.actions.ts
|   |   |
|   |   |--components
|   |   |    |
|   |   |    |--article.component.html
|   |   |    |--article.component.ts
|   |   |
|   |   |--models
|   |   |    |
|   |   |    |--article.ts
|   |   |
|   |   |--reducers
|   |   |    |
|   |   |    |--app.states.ts
|   |   |    |--article.reducer.ts
|   |   |    |--reducers.ts
|   |   |
|   |   |--app.component.ts
|   |   |--app.module.ts 
|   | 
|   |--main.ts
|   |--index.html
|   |--styles.css
|
|--node_modules
|--package.json 

以下是完整的代码： article.actions.ts

import { Action } from '@ngrx/store';
import { Article } from '../models/article';
​
export const JAVA = 'Java';
export const  ANGULAR = 'Angular';
export const  MY_ARTICLES = 'Favorite_Articles';
​
export class JavaArticlesAction implements Action {readonly type = JAVA;
}
​
export class AngularArticlesAction implements Action {readonly type = ANGULAR;
}
​
export class FavoriteArticlesAction implements Action {readonly type = MY_ARTICLES;
​constructor(public payload: Article[]) {}
}
​
export type All = JavaArticlesAction | AngularArticlesAction | FavoriteArticlesAction; 

article.ts

export interface Article {id: number;title: string;category: string;
}
​
export const JAVA_ARTICLES: Article[] = [{id: 1, title: 'Java Article 1', category: 'Java'},{id: 2, title: 'Java Article 2', category: 'Java'},
]
export const ANGULAR_ARTICLES: Article[] = [{id: 1, title: 'Angular Article 1', category: 'Angular'},{id: 2, title: 'Angular Article 2', category: 'Angular'},
]
export const FAVORITE_ARTICLES: Article[] = [{id: 1, title: 'Java Article 1', category: 'Java'},{id: 2, title: 'Angular Article 2', category: 'Angular'}
] 

app.states.ts

import { Article } from '../models/article';
​
export interface AppState {articleState: ArticleState;
}
​
export interface ArticleState {articles: Article[];
} 

article.reducer.ts

import { createFeatureSelector, createSelector } from '@ngrx/store';
import * as fromActions from '../actions/article.actions';
import { JAVA_ARTICLES, ANGULAR_ARTICLES } from '../models/article';
import { ArticleState } from './app.states';
​
export const initialState: ArticleState = { articles: []};
​
export function reducer(state = initialState, action: fromActions.All): ArticleState {switch(action.type) {case fromActions.JAVA: {return {articles: JAVA_ARTICLES};}case fromActions.ANGULAR: {return {articles: ANGULAR_ARTICLES};} case fromActions.MY_ARTICLES: {return {articles: action.payload};}    default: {return state;}} 
}
​
export const getArticleState = createFeatureSelector<ArticleState>('articleState');
​
export const getArticles = createSelector(getArticleState, (state: ArticleState) => state.articles 
); 

reducer.ts

import { ActionReducerMap, ActionReducer, MetaReducer } from '@ngrx/store';
import { AppState } from './app.states';
import * as articleReducer from './article.reducer';
import { environment } from '../../environments/environment';
​
export const reducers: ActionReducerMap<AppState> = {articleState: articleReducer.reducer
};
​
export function logger(reducer: ActionReducer<AppState>): ActionReducer<AppState> {return function(state: AppState, action: any): AppState {console.log('state', state);console.log('action', action);return reducer(state, action);};
}
​
export const metaReducers: MetaReducer<AppState>[] = !environment.production? [logger]: [];

article.component.ts

import { Store } from '@ngrx/store';
import { Component } from '@angular/core';    
import { Observable } from 'rxjs/Observable';
import * as articleReducer from '../reducers/article.reducer';
import * as fromActions from '../actions/article.actions';
import { ArticleState } from '../reducers/app.states';
import { Article, FAVORITE_ARTICLES } from '../models/article';
​
@Component({selector: 'app-article',templateUrl: 'article.component.html'
})
export class ArticleComponent {articles: Observable<Article[]>
​constructor(private store: Store<ArticleState>) {this.articles = store.select(articleReducer.getArticles);}showJavaArticles(){this.store.dispatch(new fromActions.JavaArticlesAction());}showAngularArticles(){this.store.dispatch(new fromActions.AngularArticlesAction());}showFavoriteArticles(){this.store.dispatch(new fromActions.FavoriteArticlesAction(FAVORITE_ARTICLES));}
} 

article.component.html

<button (click)="showJavaArticles()">Java Articles</button>
<button (click)="showAngularArticles()">Angular Articles</button>
<button (click)="showFavoriteArticles()">Favorite Articles</button>
<ul><li *ngFor="let article of articles | async">{{article.id}} - {{article.title}} - {{article.category}}   </li>
</ul> 

app.component.ts

import { Component } from '@angular/core';
​
@Component({selector: 'app-root',template: `<app-article></app-article>`
})
export class AppComponent {
} 

app.module.ts

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { StoreModule } from '@ngrx/store';
import { AppComponent }  from './app.component';
import { ArticleComponent }  from './components/article.component';
import { reducers, metaReducers } from './reducers/reducers';
​
@NgModule({imports: [     BrowserModule,StoreModule.forRoot(reducers, {metaReducers})],declarations: [AppComponent,ArticleComponent],providers: [
​],bootstrap: [AppComponent]
})
export class AppModule { } 

作者：neromaycry

链接：https://www.jianshu.com/p/c2d61fc76128

來源：简书