Dynamic Forms


Building handcrafted forms can be costly and time-consuming, especially if you need a great number of them, they're similar to each other, and they change frequently to meet rapidly changing business and regulatory requirements.


It may be more economical to create the forms dynamically, based on metadata that describes the business object model.


This cookbook shows you how to use formGroup to dynamically render a simple form with different control types and validation. It's a primitive start. It might evolve to support a much richer variety of questions, more graceful rendering, and superior user experience. All such greatness has humble beginnings.

本文会展示如何利用 formGroup 来动态渲染一个简单的表单,包括各种控件类型和验证规则。 这个起点很简陋,但可以在这个基础上添加丰富多彩的问卷问题、更优美的渲染以及更卓越的用户体验。

The example in this cookbook is a dynamic form to build an online application experience for heroes seeking employment. The agency is constantly tinkering with the application process. You can create the forms on the fly without changing the application code.


See the.



启动/引导 (bootstrap)

Start by creating an NgModule called AppModule.

从创建一个名叫 AppModuleNgModule 开始。

This cookbook uses reactive forms.


Reactive forms belongs to a different NgModule called ReactiveFormsModule, so in order to access any reactive forms directives, you have to import ReactiveFormsModule from the @angular/forms library.

响应式表单属于另外一个叫做 ReactiveFormsModuleNgModule,所以,为了使用响应式表单类的指令,你得从 @angular/forms 库中引入 ReactiveFormsModule 模块。

Bootstrap the AppModule in main.ts.

main.ts 中启动 AppModule

import { BrowserModule } from '@angular/platform-browser'; import { ReactiveFormsModule } from '@angular/forms'; import { NgModule } from '@angular/core'; import { AppComponent } from './app.component'; import { DynamicFormComponent } from './dynamic-form.component'; import { DynamicFormQuestionComponent } from './dynamic-form-question.component'; @NgModule({ imports: [ BrowserModule, ReactiveFormsModule ], declarations: [ AppComponent, DynamicFormComponent, DynamicFormQuestionComponent ], bootstrap: [ AppComponent ] }) export class AppModule { constructor() { } }import { enableProdMode } from '@angular/core'; import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { AppModule } from './app/app.module'; import { environment } from './environments/environment'; if (environment.production) { enableProdMode(); } platformBrowserDynamic().bootstrapModule(AppModule);

Question model


The next step is to define an object model that can describe all scenarios needed by the form functionality. The hero application process involves a form with a lot of questions. The question is the most fundamental object in the model.


The following QuestionBase is a fundamental question class.

下面的 QuestionBase 是最基础的问卷问题基类。

export class QuestionBase<T> { value: T; key: string; label: string; required: boolean; order: number; controlType: string; constructor(options: { value?: T, key?: string, label?: string, required?: boolean, order?: number, controlType?: string } = {}) { this.value = options.value; this.key = options.key || ''; this.label = options.label || ''; this.required = !!options.required; this.order = options.order === undefined ? 1 : options.order; this.controlType = options.controlType || ''; } }

From this base you can derive two new classes in TextboxQuestion and DropdownQuestion that represent textbox and dropdown questions. The idea is that the form will be bound to specific question types and render the appropriate controls dynamically.

在这个基础上,你派生出两个新类 TextboxQuestionDropdownQuestion,分别代表文本框和下拉框。这么做的初衷是,表单能动态绑定到特定的问卷问题类型,并动态渲染出合适的控件。

TextboxQuestion supports multiple HTML5 types such as text, email, and url via the type property.

TextboxQuestion 可以通过 type 属性来支持多种 HTML5 元素类型,比如文本、邮件、网址等。

import { QuestionBase } from './question-base'; export class TextboxQuestion extends QuestionBase<string> { controlType = 'textbox'; type: string; constructor(options: {} = {}) { super(options); this.type = options['type'] || ''; } }

DropdownQuestion presents a list of choices in a select box.

DropdownQuestion 表示一个带可选项列表的选择框。

import { QuestionBase } from './question-base'; export class DropdownQuestion extends QuestionBase<string> { controlType = 'dropdown'; options: {key: string, value: string}[] = []; constructor(options: {} = {}) { super(options); this.options = options['options'] || []; } }

Next is QuestionControlService, a simple service for transforming the questions to a FormGroup. In a nutshell, the form group consumes the metadata from the question model and allows you to specify default values and validation rules.

接下来定义了 QuestionControlService,一个可以把问卷问题转换为 FormGroup 的服务。 简而言之,这个 FormGroup 使用问卷模型的元数据,并允许你指定默认值和验证规则。

import { Injectable } from '@angular/core'; import { FormControl, FormGroup, Validators } from '@angular/forms'; import { QuestionBase } from './question-base'; @Injectable() export class QuestionControlService { constructor() { } toFormGroup(questions: QuestionBase<any>[] ) { let group: any = {}; questions.forEach(question => { group[question.key] = question.required ? new FormControl(question.value || '', Validators.required) : new FormControl(question.value || ''); }); return new FormGroup(group); } }

Question form components


Now that you have defined the complete model you are ready to create components to represent the dynamic form.


DynamicFormComponent is the entry point and the main container for the form.

DynamicFormComponent 是表单的主要容器和入口点。

<div> <form (ngSubmit)="onSubmit()" [formGroup]="form"> <div *ngFor="let question of questions" class="form-row"> <app-question [question]="question" [form]="form"></app-question> </div> <div class="form-row"> <button type="submit" [disabled]="!form.valid">Save</button> </div> </form> <div *ngIf="payLoad" class="form-row"> <strong>Saved the following values</strong><br>{{payLoad}} </div> </div>import { Component, Input, OnInit } from '@angular/core'; import { FormGroup } from '@angular/forms'; import { QuestionBase } from './question-base'; import { QuestionControlService } from './question-control.service'; @Component({ selector: 'app-dynamic-form', templateUrl: './dynamic-form.component.html', providers: [ QuestionControlService ] }) export class DynamicFormComponent implements OnInit { @Input() questions: QuestionBase<any>[] = []; form: FormGroup; payLoad = ''; constructor(private qcs: QuestionControlService) { } ngOnInit() { this.form = this.qcs.toFormGroup(this.questions); } onSubmit() { this.payLoad = JSON.stringify(this.form.value); } }

It presents a list of questions, each bound to a <app-question> component element. The <app-question> tag matches the DynamicFormQuestionComponent, the component responsible for rendering the details of each individual question based on values in the data-bound question object.

它代表了问卷问题列表,每个问题都被绑定到一个 <app-question> 组件元素。 <app-question> 标签匹配到的是组件 DynamicFormQuestionComponent,该组件的职责是根据各个问卷问题对象的值来动态渲染表单控件。

<div [formGroup]="form"> <label [attr.for]="question.key">{{question.label}}</label> <div [ngSwitch]="question.controlType"> <input *ngSwitchCase="'textbox'" [formControlName]="question.key" [id]="question.key" [type]="question.type"> <select [id]="question.key" *ngSwitchCase="'dropdown'" [formControlName]="question.key"> <option *ngFor="let opt of question.options" [value]="opt.key">{{opt.value}}</option> </select> </div> <div class="errorMessage" *ngIf="!isValid">{{question.label}} is required</div> </div>import { Component, Input } from '@angular/core'; import { FormGroup } from '@angular/forms'; import { QuestionBase } from './question-base'; @Component({ selector: 'app-question', templateUrl: './dynamic-form-question.component.html' }) export class DynamicFormQuestionComponent { @Input() question: QuestionBase<any>; @Input() form: FormGroup; get isValid() { return this.form.controls[this.question.key].valid; } }

Notice this component can present any type of question in your model. You only have two types of questions at this point but you can imagine many more. The ngSwitch determines which type of question to display.

请注意,这个组件能代表模型里的任何问题类型。目前,还只有两种问题类型,但可以添加更多类型。可以用 ngSwitch 决定显示哪种类型的问题。

In both components you're relying on Angular's formGroup to connect the template HTML to the underlying control objects, populated from the question model with display and validation rules.

在这两个组件中,你依赖 Angular 的 formGroup 来把模板 HTML 和底层控件对象连接起来,该对象从问卷问题模型里获取渲染和验证规则。

formControlName and formGroup are directives defined in ReactiveFormsModule. The templates can access these directives directly since you imported ReactiveFormsModule from AppModule.

formControlNameformGroup 是在 ReactiveFormsModule 中定义的指令。这个模板之所以能使用它们,是因为你曾从 AppModule 中导入了 ReactiveFormsModule

Questionnaire data


DynamicFormComponent expects the list of questions in the form of an array bound to @Input() questions.

DynamicForm 期望得到一个问题列表,该列表被绑定到 @Input() questions 属性。

The set of questions you've defined for the job application is returned from the QuestionService. In a real app you'd retrieve these questions from storage.

QuestionService 会返回为工作申请表定义的那组问题列表。在真实的应用程序环境中,你会从数据库里获得这些问题列表。

The key point is that you control the hero job application questions entirely through the objects returned from QuestionService. Questionnaire maintenance is a simple matter of adding, updating, and removing objects from the questions array.

关键是,你完全根据 QuestionService 返回的对象来控制英雄的工作申请表。 要维护这份问卷,只要非常简单地添加、修改和删除 questions 数组中的对象就可以了。

import { Injectable } from '@angular/core'; import { DropdownQuestion } from './question-dropdown'; import { QuestionBase } from './question-base'; import { TextboxQuestion } from './question-textbox'; @Injectable() export class QuestionService { // TODO: get from a remote source of question metadata // TODO: make asynchronous getQuestions() { let questions: QuestionBase<any>[] = [ new DropdownQuestion({ key: 'brave', label: 'Bravery Rating', options: [ {key: 'solid', value: 'Solid'}, {key: 'great', value: 'Great'}, {key: 'good', value: 'Good'}, {key: 'unproven', value: 'Unproven'} ], order: 3 }), new TextboxQuestion({ key: 'firstName', label: 'First name', value: 'Bombasto', required: true, order: 1 }), new TextboxQuestion({ key: 'emailAddress', label: 'Email', type: 'email', order: 2 }) ]; return questions.sort((a, b) => a.order - b.order); } }

Finally, display an instance of the form in the AppComponent shell.

最后,在 AppComponent 里显示出表单。

import { Component } from '@angular/core'; import { QuestionService } from './question.service'; @Component({ selector: 'app-root', template: ` <div> <h2>Job Application for Heroes</h2> <app-dynamic-form [questions]="questions"></app-dynamic-form> </div> `, providers: [QuestionService] }) export class AppComponent { questions: any[]; constructor(service: QuestionService) { this.questions = service.getQuestions(); } }

Dynamic Template


Although in this example you're modelling a job application for heroes, there are no references to any specific hero question outside the objects returned by QuestionService.

在这个例子中,虽然你是在为英雄的工作申请表建模,但是除了 QuestionService 返回的那些对象外,没有其它任何地方是与英雄有关的。

This is very important since it allows you to repurpose the components for any type of survey as long as it's compatible with the question object model. The key is the dynamic data binding of metadata used to render the form without making any hardcoded assumptions about specific questions. In addition to control metadata, you are also adding validation dynamically.

这点非常重要,因为只要与问卷对象模型兼容,就可以在任何类型的调查问卷中复用这些组件。 这里的关键是用到元数据的动态数据绑定来渲染表单,对问卷问题没有任何硬性的假设。除控件的元数据外,还可以动态添加验证规则。

The Save button is disabled until the form is in a valid state. When the form is valid, you can click Save and the app renders the current form values as JSON. This proves that any user input is bound back to the data model. Saving and retrieving the data is an exercise for another time.

表单验证通过之前,保存按钮是禁用的。验证通过后,就可以点击保存按钮,程序会把当前值渲染成 JSON 显示出来。 这表明任何用户输入都被传到了数据模型里。至于如何储存和提取数据则是另一话题了。

The final form looks like this:



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