angular - 如何在 Angular 中单击按钮时将 FormControl 动态添加到 FormArray？

Question

如何添加 formcontrol(option)动态在 formarray ?我想动态添加问题到 formarray .单击按钮后，它应该更新显示。我正在使用 Angular 7。
组件代码

ngOnInit() {
  this.quizForm = this.fb.group({
    questions: this.fb.array([]),
    questions2: this.fb.array([]),
  });
}
    
//creating formcontrol
createItem(): FormGroup {
  return this.fb.group({
    ques: '',
  });
}
    
//pushing code
genField() {
  this.message = true;
  this.questions = this.quizForm.get('questions') as FormArray;
  this.questions.push(this.createItem());
}

HTML模板
我想在按钮单击时动态添加表单控件选项，表单控件应该在 formArrayName="questions" 内.

<form [formGroup]="quizForm" class="adjust-form">
  <div formArrayName="questions" 
    *ngFor="let item of quizForm.get('questions').controls; let i = index;">
    <div class="col-md-10 col-sm-6 mt-3 mb-3" [formGroupName]="i">
      <label>{{i +1}} - {{question}} </label>
      <i class="flaticon-delete"    
          (click)="quizForm.get('questions').controls.splice(i,1) "
          style="font-size: 9px;padding-left: 80px;">
      </i>
      <div class="row">
        <input type="text" class="form-control col-10"
            [(ngModel)]="item.ques" formControlName="ques"
            placeholder="Enter your question" required>
        <button *ngIf="i == 0" (click)="genField()" type="button"
            class="btn btn-secondary btn-elevate btn-circle btn-icon ml-4">
            <i class="flaticon2-plus"></i>
        </button>
      </div>
      <div *ngIf="item.touched && item.invalid" class="kt-font-danger text-left">
        <p>required</p>
      </div>
    </div>
  </div>
</form>

Answer 1

此示例动态地将电子邮件字段添加到响应式(Reactive)表单。这将用于使用户能够添加多个电子邮件地址(例如家庭和工作)。
此演示具有以下依赖项:Angular 8、Angular Material , Bootstrap 4
最终结果 ( Stackblitz Demo )

步骤 1:定义表单模型

constructor(private formBuilder: FormBuilder) { }

ngOnInit() {
  this.emailForm = this.formBuilder.group({
    emails: this.formBuilder.array([this.createEmailFormGroup()])
  });
}

第二步:定义一个动态构造new的方法 FormGroup

private createEmailFormGroup(): FormGroup {
  return new FormGroup({
    'emailAddress': new FormControl('', Validators.email),
    'emailLabel': new FormControl('')
  })
}

第三步:定义动态添加新的方法 FormGroup到 FormArray

public addEmailFormGroup() {
  const emails = this.emailForm.get('emails') as FormArray
  emails.push(this.createEmailFormGroup())
}

第 4 步(可选):定义删除方法 FormGroup

public removeOrClearEmail(i: number) {
  const emails = this.emailForm.get('emails') as FormArray
  if (emails.length > 1) {
    emails.removeAt(i)
  } else {
    emails.reset()
  }
}

步骤 5:创建 HTML 表单模板

<form [formGroup]="emailForm">
  <div formArrayName="emails">
    <div class="row" *ngFor="let email of emailForm.get('emails').controls; let i = index"
        [formGroupName]="i">

请注意，在 formArrayName 内element，动态邮箱 FormGroups根据数组索引命名。
最终形式

<mat-toolbar color="primary">
    Angular Form Demo - Dynamically add form controls
</mat-toolbar>

<form class="basic-container" [formGroup]="emailForm">
  <div formArrayName="emails">
    <div class="row" *ngFor="let email of emailForm.get('emails').controls; let i = index"
        [formGroupName]="i">

      <div class="col-1">
        <mat-icon class="mt-3">email</mat-icon>
      </div>

      <mat-form-field class="col-4">
        <input matInput formControlName="emailAddress" placeholder="Email" autocomplete="email">
        <mat-error *ngFor="let validation of validationMsgs.emailAddress">
          <div *ngIf="email.get('emailAddress').hasError(validation.type)">
            {{validation.message}}
          </div>
        </mat-error>
      </mat-form-field>

      <mat-form-field class="col-4">
        <mat-label>Label</mat-label>
        <mat-select formControlName="emailLabel">
          <mat-option *ngFor="let label of emailLabels" [value]="label">
            {{label}}
          </mat-option>
        </mat-select>
      </mat-form-field>

      <div class="col-3">
        <button class="float-left" mat-icon-button color="primary" aria-label="Remove/clear"
            (click)="removeOrClearEmail(i)" matTooltip="Remove">
          <mat-icon>highlight_off</mat-icon>
        </button>
        <button class="float-left" mat-icon-button color="primary" aria-label="Add"
            (click)="addEmailFormGroup()" matTooltip="Add">
          <mat-icon>add_circle_outline</mat-icon>
        </button>
      </div>
    </div>
  </div>
</form>

最终组件

import {Component} from '@angular/core';
import {FormBuilder, FormArray, FormControl, FormGroup, Validators} from '@angular/forms';

@Component({
  selector: 'form-app',
  templateUrl: 'app.component.html'
})
export class AppComponent {
  public emailForm: FormGroup;
  public emailLabels = ['Home', 'Work', 'Other'];
  public validationMsgs = {
    'emailAddress': [{ type: 'email', message: 'Enter a valid email' }]
  }

  constructor(private formBuilder: FormBuilder) { }

  ngOnInit() {
    this.emailForm = this.formBuilder.group({
      emails: this.formBuilder.array([this.createEmailFormGroup()])
    });
  }

  public addEmailFormGroup() {
    const emails = this.emailForm.get('emails') as FormArray
    emails.push(this.createEmailFormGroup())
  }

  public removeOrClearEmail(i: number) {
    const emails = this.emailForm.get('emails') as FormArray
    if (emails.length > 1) {
      emails.removeAt(i)
    } else {
      emails.reset()
    }
  }

  private createEmailFormGroup(): FormGroup {
    return new FormGroup({
      'emailAddress': new FormControl('', Validators.email),
      'emailLabel': new FormControl('')
    })
  }
}