Angular: How to dynamically add FormControl to FormArray on button click

问题

How can I add a formcontrol(option) dynamically in formarray? I want to add in questions formarray. Onbutton click it should display. I'm using angular 7.

//ngOnInit creating form
    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());
    }

Here's my HTML code. I want to add form control option dynamically on button click and form control should be inside the formArrayName="questions".

    <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>

回答1:

This example dynamically adds email fields to a reactive form. This would be used to enable users to add multiple email addresses (e.g. Home and Work).

This demo has the following dependencies: Angular 8, Angular Material, Bootstrap 4

End Result (Stackblitz Demo)

Step 1: Define the form model

constructor(private formBuilder: FormBuilder) { }

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

Step 2: Define a method to dynamically construct new FormGroup

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

Step 3: Define a method to dynamically add new FormGroup to the FormArray

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

Step 4 (Optional): Define method to delete FormGroup

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

Step 5: Create the HTML form template

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

Note that within the formArrayName element, the dynamic email FormGroups are named based on the array index.

Final Form

<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>

Final Component

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('')
    })
  }
}

来源：https://stackoverflow.com/questions/59033703/angular-how-to-dynamically-add-formcontrol-to-formarray-on-button-click