坂本  健一

坂本 健一

1659579780

Angular で複数の読み込み状態を管理する

Angular アプリケーションを開発する場合、おそらく HTTP リクエストを実行する必要があります。別のバックエンド アプリケーションまたは外部 API からデータをフェッチする場合でも、アプリケーションはある時点で応答を待たなければならない場合があります。

Web アプリケーションで HTTP 要求の状態を適切に処理することは、一般的なユース ケースです。大規模なコードベースでは、すぐにアーキテクチャの重要な問題になります。この問題は、Angular が冗長なフレームワークである以上に重要です。

この文脈では、この懸念に対するあなたの解決策は次のとおりでなければなりません。

  • コードベースを読みやすくするのに十分なほどシンプル
  • コードベースを正常に保ち、新しいページやコンポーネントを作成するときに時間を節約するのに十分な再利用可能
  • アプリケーションのさまざまなユースケースを処理するのに十分な適応性

この記事は、これら 3 つの側面に関して、Angular でのリクエストの読み込みまたはエラーを処理するいくつかの方法を提示することを目的としています。

エラーメッセージとローダーの表示を気にする必要があるのはなぜですか

これに苦労する最初の主な理由は、私たちがユーザーを気にかけているからです。アプリケーションで何が起こっているのかを簡単に理解してもらいたいので、非同期操作が実行されるのを待っている間にボタンを 10 回クリックする必要はありません。

したがって、非同期処理を実行するときに、できるだけ多くのフィードバックを提供することが重要です。

RxJS

Angular 非同期実行管理は、基本的に RxJS を使用したリアクティブ プログラミングに依存しています。したがって、ここで紹介するすべてのパターンにはこのライブラリが含まれます。

この記事では、 と について言及ObservablesBehaviorSubjectsます。リアクティブ プログラミング、特にこれら 2 つのオブジェクトに慣れていない場合は、ライブラリの非常によく設計されたドキュメントを確認することをお勧めします。

コンポーネント状態を使用して 1 つの要求状態を管理する

原理

リクエストを追跡する最も簡単な方法は、コンポーネント内で直接監視することです。

猫の品種のかわいい小さな写真を表示するための API を構築するとしましょう。

コンポーネントは、リクエストの現在の状態 (読み込み中とエラー) を保存するための 2 つのブール属性を宣言し、これらの属性はデータ取得操作全体で更新されます。

コンポーネント内での外観

@Component({
  selector: 'app-fetch-breeds',
  templateUrl: './fetch-breeds.component.html',
})
export class FetchBreedsComponent {
  constructor(private myService: MyService) {}

  loading = false;
  error = false;
  errorMessage = '';

  fetchBreeds() {
    // Reset request error state data
    this.error = false;
    this.errorMessage = '';

    // Set the component in a loading state
    this.loading = true;

    // Start the fetch event pipeline involving :
    this.myService.fetchBreeds().pipe(
      // A handler which is called when our service triggers an error and
      // which is dedicated to setting the error in a corresponding state
      catchError(err => {
        this.error = true;
        this.errorMessage = err.message; // Or whatever error message you like
      })
      // A callback which is always called whether an error has been triggered
      // or not.
      // It is responsible for setting the component in a non-loading state.
      finalize(() => {
        this.loading = false;
      })
    )
    .subscribe();
  }
}
<div>
  <!-- If we are fetching the data, we display a loader -->
  <app-loader *ngIf="loading"></app-loader>
  <button (click)="fetchBreeds()">See these magnificent cats!</button>
  <!-- If there is an error (and we are done waiting for a response), we display it -->
  <app-error-message *ngIf="!loading && error">
    {{ errorMessage }}
  </app-error-message>
</div>

サービス内のリクエスト状態の管理

なぜこのロジックをサービスに委任するのですか?

Angular アプリケーションでサービスを使用すると、多くの利点が得られます (DRY 原則、効率的なテストなど)。私たちの場合、コンポーネント/他のサービス間でデータを永続化および共有することもできます。

また、抽象化も可能です。コンポーネントは UI 表示専用であり、サービスはコンポーネントの内部の複雑なロジックを処理します。

ケース 1 - 状態が複数のコンポーネント間で共有されている

cat エンティティに基づいて 2 つの機能を提供する 2 つのコンポーネントがあるとします。1 つのページには品種の写真が表示され、もう 1 つのページにはこれらの品種に関する技術的な詳細が表示されます。

サービス内でロード状態を処理するためのアーキテクチャの例

このアーキテクチャには、リクエストの送信、エラーのキャッチ、その間の読み込み状態の処理を担当するロジックの複製が含まれます。

このロジックは専用のサービスに移動できます。これにより、ロード情報用に 1 つ、エラー用に 1 つのオブザーバブルが公開されます。

@Injectable()
export class CatBreedsService {
    constructor(private http: HttpClient) {}

    private _loadingSubject = new BehaviorSubject<boolean>(false)
    isLoading$: this._loadingSubject.asObservable();

    // We expose observables because we want our components to have a read access
    // but no write access to the information

    private _errorSubject = new BehaviorSubject<string | null>(null);
    erros$: this._errorSubject.asObservable();

    fetchBreeds(): Observable<CatBreed[]> {
        this._loadingSubject.next(true);
        this._errorSubject.next(null);
        return this.http.get('/cat-breed').pipe(
            catchError(err => {
                this._errorSubject.next(err);
                return of([]);
            }),
            finalize(() => this._loadingSubject.next(false))
        )
    }
}

これで、コンポーネントはサービスからフェッチ ヘルパーを呼び出すだけで済み、エンティティに関する読み込み/エラー状態の情報がアプリケーション全体で共有されます。

@Component({
  selector: "app-list-cat-breeds",
  templateUrl: "./list-cat-breeds.component.html",
})
export class ListCatBreedsComponent implements OnInit {
  constructor(private catBreedsService: CatBreedsService) {}

  isLoading$ = this.catBreedsService.loading$;
  hasErrors$ = this.catBreedsService.errors$;

  ngOnInit() {
    this.catBreedsService.fetchBreeds.subscribe();
  }
}

サービス内で複数のリクエスト状態を管理する

ケース 2 - 同時実行の問題

使用例: オートコンプリート入力の複数回の出現

また、複数のコンテキストで同じ操作に対してリクエストを実行する必要がある場合にも遭遇する可能性があります。

たとえば、各入力が変更時に自動提案データを動的にフェッチし、更新の実行中にローダーを表示するフォームがあるとします。このリクエストの状態を処理するために独自のサブジェクトを作成すると、同時実行の問題が発生します。

このコンテキストでの具体的な例は、品種を猫の写真に関連付けることができるページです。

サービス内で複数の読み込み状態を処理するためのアーキテクチャの例

副作用の問題

この場合、すべての入力に対して読み込みサブジェクトが 1 つしかないため、いずれかの入力を変更すると、他のすべてのサブジェクトが読み込み状態またはエラー状態になります。

観察可能な提案でも同じことが起こります。アプリケーションで不要なレンダリングがトリガーされ、アプリケーションのパフォーマンスに壊滅的な結果をもたらす可能性があります。

副作用は、このコンポーネントを複数の部分に分解する必要があることを意味します

ローディングオブザーバブルとエラーオブザーバブルを含む複雑な状態を持つことで、この問題を処理できます。以下のコードは、そのような実装を示しています。

export interface InputState {
  loading$: BehaviorSubject<boolean>;
  error$: BehaviorSubject<string >;
}

@Component({
  selector: 'app-cat-breed-form',
  templateUrl: './cat-breed-form.component.html',
})
export class CatBreedFormComponent implements OnInit {
  inputs = ['input1', 'input2', 'input3'];
  inputsState: { [key: string]: InputState } = {};

  ngOnInit() {
    this.inputs.forEach(input => {
      this.inputsState[input] = {
        loading$: new BehaviorSubject(false),
        error$: new BehaviorSubject<string | null>(null)
      };
    }, {});
  }

  setLoading(inputId: string, value: boolean) {
    this.inputsState[inputId].loading$.next(value)
  }

  setError(inputId: string, value: string | null) {
    this.inputsState[inputId].error$.next(value)
  }

  getLoading(inputId: string) {
    return this.inputsState[inputId].loading$.asObservable()
  }

  getError(inputId: string) {
    return this.inputsState[inputId].error$.asObservable()
  }

  updateField(inputId: string) {
    this.setLoading(inputId, true)
    this.project$.pipe(
      take(1),
      catchError(err => {
        this.setError(inputId, err)
      }),
      finalize(() => this.setLoading(inputId, err))
    ).subscribe(() => { // do your stuff })}
  }
}

いくつかのコメント:

  • コンポーネントのロジックは複雑になっています。
  • フェッチ ロジックをサービスにデポートすることはできません。少なくとも、コンポーネント内から読み込み/エラー状態を管理する必要があります。
  • 読み取り可能なテンプレートを作成するには、おそらく実装する必要がありますgetters/setters

したがって、コンポーネントのtsファイルに記述されるコードが増えます。

これをより単純なコンポーネントに分解すると (この場合はフィールド コンポーネントを実装することを意味します)、並行性のない最初のケースに戻ります。

次のような登録機能を公開する専用サービスを作成できます。

  • 入力でIDを取ります
  • 「変更」イベントが検索をトリガーする formControl を作成します
  • formControl と、関連する読み込み、エラー、およびオートコンプリートの提案オブザーバブルを返します。
@Injectable()
export class SearchService implements OnDestroy {
  constructor(private http: HttpClient) {}

  subscriptions: Subscription[] = [];

  registerControl<T>(id: string, initialvalue: T) {
    const control = new FormControl(initialvalue);
    const _loadingSubject = new BehaviorSubject<boolean>(false);
    const _errorsSubject = new BehaviorSubject<string | null>(null);
    const _suggestedSubject = new BehaviorSubject<T[]>([]);
    this.subscriptions.push(
      control.valueChanges
        .pipe(
          switchMap((query: string | null) => {
            if (query !== null && query.length > 0) {
              return this.searchOnQuery<T[]>(query).pipe(
                catchError(err => {
                  _errorsSubject.next(err);
                  return of([]);
                }),
                finalize(() => _loadingSubject.next(false))
              );
            }
            return of([]);
          }),
          tap(suggestions => _suggestedSubject.next(suggestions))
        )
        .subscribe()
    );

    return [
	control,
	_loadingSubject.asObservable(),
	_errorsSubject.asObservable(),
	_suggestedSubject.asObservable()
    ];
  }

  private searchOnQuery<T>(query: string) {
    return this.http.get<T>('/search', {
      params: {
        query
      }
    });
  }

  ngOnDestroy() {
    this.subscriptions.forEach(sub => sub.unsubscribe());
  }
}

次に、このサービス内で新しい入力を登録する必要があります。

@Component({
  selector: 'app-cat-breed-autocomplete-input',
  templateUrl: './cat-breed-autocomplete.component.html',
  styleUrls: ['./cat-breed-autocomplete.component.scss']
})
export class CatBreedAutocompleteInput implements OnInit {
  @Input() initialValue: Entity;
  @Input() autocompleteId: string;

  control: FormControl = new FormControl();
  loading$: Observable<boolean> = of(false);
  error$: Observable<boolean> = of(null);
  suggestions$: Observable<boolean> = of([]);

  constructor(private searchService: SearchService) {}

  ngOnInit() {
    const [control, loading$, error$, suggestions$] = this.searchService.register<CatBreed>(
      this.autocompleteId,
      this.initialValue
    )
    this.control = control;
    this.loading$ = loading$;
    this.error$: error$;
    this.suggestions$ = suggestions$;
  }
}

これら 4 つのオブザーバブルがテンプレートで使用できるようになり、非同期パイプで使用できるようになりました。

FormControl APIを介して独自のイベント管理システムを備えているため、これにより、すべての入力が独立して動作できるようになります。

結論

この記事では、RxJS を使用してリクエストの読み込み状態を処理する 2 つの異なる方法と、これを Angular アーキテクチャに組み込む方法について説明しました。

1 つのコンポーネントで処理するローダーは 1 つだけなので、UI ロジックをコンポーネントに実装してもかまいません。同時に複数のローダーを使用すると、物事が簡単に混乱するため、複数のオートコンプリート入力の場合にこの新しい複雑さを処理する方法を確認しました。

ソース: https://blog.theodo.com/2021/01/managing-requests-loading-state-angular/

#angular #rxjs 

What is GEEK

Buddha Community

Angular で複数の読み込み状態を管理する
Christa  Stehr

Christa Stehr

1598940617

Install Angular - Angular Environment Setup Process

Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

  1. Installing Node.js and npm
  2. Installing Angular CLI
  3. Creating workspace
  4. Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Angular environment setup

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

  • Node.js
  • npm Package Manager
Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

  1. npm -v

Installing Angular CLI

  • Open Terminal/Command Prompt
  • To install Angular CLI, run the below command:
  1. npm install -g @angular/cli

installing angular CLI

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

  1. ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

  • Using CLI
  • Using Visual Studio Code
1. Using CLI

To create a workspace:

  • Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
  • Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:
  1. Ng new YourAppName

create angular workspace

  • After running this command, it will prompt you to select from various options about the CSS and other functionalities.

angular CSS options

  • To leave everything to default, simply press the Enter or the Return key.

angular setup

#angular tutorials #angular cli install #angular environment setup #angular version check #download angular #install angular #install angular cli

Roberta  Ward

Roberta Ward

1593184320

Basics of Angular: Part-1

What is Angular? What it does? How we implement it in a project? So, here are some basics of angular to let you learn more about angular.

Angular is a Typescript-based open-source front-end web application platform. The Angular Team at Google and a community of individuals and corporations lead it. Angular lets you extend HTML’s syntax to express your apps’ components clearly. The angular resolves challenges while developing a single page and cross-platform applications. So, here the meaning of the single-page applications in angular is that the index.html file serves the app. And, the index.html file links other files to it.

We build angular applications with basic concepts which are NgModules. It provides a compilation context for components. At the beginning of an angular project, the command-line interface provides a built-in component which is the root component. But, NgModule can add a number of additional components. These can be created through a template or loaded from a router. This is what a compilation context about.

What is a Component in Angular?

Components are key features in Angular. It controls a patch of the screen called a view. A couple of components that we create on our own helps to build a whole application. In the end, the root component or the app component holds our entire application. The component has its business logic that it does to support the view inside the class. The class interacts with the view through an API of properties and methods. All the components added by us in the application are not linked to the index.html. But, they link to the app.component.html through the selectors. A component can be a component and not only a typescript class by adding a decorator @Component. Then, for further access, a class can import it. The decorator contains some metadata like selector, template, and style. Here’s an example of how a component decorator looks like:

@Component({
    selector: 'app-root',
    templateUrl: 'app.component.html',
    styleUrls: ['app.component.scss']
})

Role of App Module

Modules are the package of functionalities of our app. It gives Angular the information about which features does my app has and what feature it uses. It is an empty Typescript class, but we transform it by adding a decorator @NgModule. So, we have four properties that we set up on the object pass to @NgModule. The four properties are declarations, imports, providers, and bootstrap. All the built-in new components add up to the declarations array in @NgModule.

@NgModule({
declarations: [
  AppComponent,
],
imports: [
  BrowserModule,
  HttpClientModule,
  AppRoutingModule,
  FormsModule
],
bootstrap: [AppComponent]
})

What is Data Binding?

Data Binding is the communication between the Typescript code of the component and the template. So, we have different kinds of data binding given below:

  • When there is a requirement to output data from our Typescript code in the HTML template. String interpolation handles this purpose like {{data}} in HTML file. Property Binding is also used for this purpose like [property] = “data”.
  • When we want to trigger any event like clicking a button. Event Binding works while we react to user events like (event) = “expression”.
  • When we can react to user events and output something at the same time. Two-way Binding is used like [(ngModel)] = “data”.

image for understanding data binding

#angular #javascript #tech blogs #user interface (ui) #angular #angular fundamentals #angular tutorial #basics of angular

Ayyaz Zafar

1624138795

Angular Material Autocomplete - Multiple Use Cases covered

Learn How to use Angular Material Autocomplete Suggestions Search Input. I covered multiple use cases.

Please watch this video. I hope this video would be helpful for you to understand it and use it in your projects

Please subscribe: https://www.youtube.com/channel/UCL5nKCmpReJZZMe9_bYR89w

#angular #angular-material #angular-js #autocomplete #angular-material-autocomplete #angular-tutorial

Mansi Gandhi

Mansi Gandhi

1625232772

Why Choose AngularJS framework for the enterprise? | Angular development Company - CMARIX

Although Angular JS has bought headlines over the domain of Web application development, its relevance downtime does not offer any guarantee. Since the JavaScript application is the child of Google, its web features may have some value. Angular JS enables the developer to write most of the code in HTML which brings the application together. Such potentiality and simplicity of the program from the Angular Development Company made Angular popular among JavaScripts.

But the real question arises on the integrity and the safety Angular can provide to the industry. Angular regularly updates its libraries to fix security issues over earlier versions. However, the private and customized Angular versions fall back from the latest versions. These versions might lack the crucial security patches. As a piece of advice, developers can share their improvement requests in the community.

Backward compatibility indicates that the updated versions can function with the outdated versions. Hence, it can simplify the migration procedures to the latest Angular version. Some portions of the AngularJS apps need lazy loading to ease the update and to facilitate the transfer of large projects.

Since AngularJS tends to spoil backward compatibility, it might cause future problems in a program.

The Changing Face of Frameworks

There were several ups and downs in the Web application market over the past. A few years ago, SproutCore ruled the throne as a top framework. However, according to Google search trends, BackboneJS later stole the spotlight which again passed over to EmberJS. But, there remains no comparison for AngularJS.

Birthed by Adam Abrons and Misko Hevery, the Brat Tech engineers in 2009, the Angular Development Company AngularJS took a swift transition to open-source. When Misko Hevery joined Google, he continued to develop Angular JS. The platform began to earn its place by December of 2012 according to Google Trends.

In the year 2015, the potential of AngularJS surpassed other frameworks and offered job placements for many developers. However, AngularJS is not entirely without competition as Facebook came up with ReactJS. Hence, there is a race to show which surpasses the other. But, according to Jeff Schroeder, among the native apps, React elevates mobile app development to higher levels.

Continuous Development in Angular JS

AngularJS has high popularity yet, the developers break backward compatibility on a regular basis. Therefore, the supporters of AngularJS have to learn the AngularJS framework again and again. A critic of AngularJS – Danny Tuppeny, points out that the framework is unstable as it offers short-term support. The developers develop the framework every now and then which can puzzle its users. However, a mobile Web developer by the name of Nene Bodonkor indicates another factor. The frameworks become satisfactory and since they fail to keep up with the market requirements, change becomes crucial.

On the contrary, Yehuda Katz, the creator of EmberJS suggests that the fast-paced lifestyle needs to slow down. Therefore, these constant changes can compel people to reduce and balance their pace. Both, ReactJS from Facebook and EmberJS fight to achieve maximum backward compatibility. Such a characteristic helps these frameworks to come to use for an enterprise. But, AngularJS still has its upper hand over its competitors.

The simple-to-learn design of the Angular Framework with various functions

A legacy system includes few characteristics like old technology that are not compatible with the present systems. These systems do not remain available for purchase from distributors or vendors. These legacy systems cannot update nor patch up by themselves as the developer or vendor stops its maintenance.

The CTO of a mobile and Web app development company Monsoon, Michi Kono agreed on the decisions. But he also commented that the core developers at AngularJS miscommunicated the information. As the AngularJS framework has its uses in Google, they can use the platform for legacy versions and supporting enterprises. According to Michi Kono, AngularJS can promise a safe approach for its use in enterprises. The framework of Angular Development Company USA makes learning simple as it lacks strong convention opinions. The framework is easy for developers to learn and Angular has its applications on other parallel technologies. Vast organizations that have a demand for on-scale development and hiring procedures can use the framework to their advantage.

The low level of Angular appears more as a toolbox than a framework. Such an approach makes Angular useful on a wide variety of utility functions. The developer can use the JavaScript framework to add a single website button through a separate framework. Major companies like Google, Facebook and Microsoft aim to improve JavaScript to match entrepreneur requirements. Since AtScript or the typed JavaScript from Google, will form the backbone of AngularJS 2.0, several developers shall prefer to leverage it.

The Best Fit

AngularJS has several promising aspects for developers from different enterprises to try. But the JavaScript framework undergoes several alterations by its developers. Yet, some of the JavaScript frameworks grab the focus of various users for which they remain in maintenance. Therefore, according to Brian Leroux, the Adobe Web developer, there are two options left. Developers can either imprison themselves within vast rewrites with no forward progress. Or Hire angular developers who can focus their attention to optimize the website architecture. Therefore, developers need to stay up-to-date with the current developments in the web application frameworks like AngularJS.

AngularJS frameworks carry lots of potential in real-time markets. But, the developers need to stay up-to-date to tackle the regular changes in its infrastructure.

#hire angular developers #angular #angular web development #angular development company #angular services #angularjs

Ajay Kapoor

1624334049

Top Angular JS Development Company in India | Angularjs Development

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Angularjs development company in India

#angular js development company #angular js web development #angular js development company in india #angular development company in india #angular development india #angular development company india