input / ion-input in reactive forms - problems with ChangeDetectionStrategy

问题

I have following template for input fields in multiple forms (please ignore objToKeys - it is custom pipe and it works) :

<div [formGroup]="form">
  <ion-item>
    <ion-label color="primary" position="floating">{{ label }}</ion-label>

    <ion-input type="text" formControlName="{{ controlName }}"></ion-input>
  </ion-item>

  <div *ngIf="form.controls[controlName].touched && form.controls[controlName].errors" class="form-error-messages">
    <div *ngFor="let key of form.controls[controlName].errors | objToKeys">
      <ion-icon color="danger" name="alert-outline"></ion-icon>
      <ion-label class="ion-padding-start" color="danger" class="ion-align-items-end">
        {{ form.controls[controlName].errors[key].message }}
      </ion-label>
    </div>
  </div>
</div>

I tried to get this template simplified by creating a custom component : component.ts

import { Component, OnInit, Input } from '@angular/core';
import { FormGroup } from '@angular/forms';

@Component({
  selector: 'app-form-input',
  templateUrl: './form-input.component.html',
  styleUrls: ['./form-input.component.scss'],
})
export class FormInputComponent implements OnInit {
  @Input() label: string;
  @Input() controlName: string;
  @Input() form: FormGroup;
  constructor() {}

  ngOnInit() {}
}

component.html

<div [formGroup]="form">
  <ion-item>
    <ion-label color="primary" position="floating">{{ label }}</ion-label>
    <ion-input type="text" formControlName="{{ controlName }}"></ion-input>
  </ion-item>
  <div *ngIf="form.controls.name.touched && form.controls.name.errors" class="form-error-messages">
    <div *ngFor="let key of form.controls.name.errors | objToKeys">
      <ion-icon color="danger" name="alert-outline"></ion-icon>
      <ion-label class="ion-padding-start" color="danger" class="ion-align-items-end">
        {{ form.controls.name.errors[key].message }}
      </ion-label>
    </div>
  </div>
</div>

Please note that in the above html, the input is wrapped in a div with [formGroup]="form". I I do not wrap it then Angular complains that the formControl is not enclosed inside the formgroup. However note that the parent component that calls it, has the [formGroup] attribute.

<form [formGroup]="form" (ngSubmit)="onSubmit()" #formRef="ngForm">
  <app-form-input [label]="'Insitution Name'" [controlName]="'name'" [form]="form"></app-form-input>


  <app-actions
    slot="end"
    [itemType]="'summary'"
    [actionMode]="'answer'"
    [formMode]="formMode"
    (saveSummary)="submitForm()"
    (cancelSummary)="onCancel()"
  ></app-actions>
</form>

So why was angular complaining initially, is my solution correct? Is this a good way to achieve component reuse?

回答1:

There are several questions on the same topic. I posted one in the link.Do an exhaustive search on this site. Apparently it is a common error.

My Solution was based on this blog by Netanel Basal:

I changed the ChangeDetectionStarategy on the parent component to : changeDetection: ChangeDetectionStrategy.OnPush,

This change got rid of the error:

Expression has changed after it was checked. Previous value: 'ng-valid: true'. Current value: 'ng-valid: false'

来源：https://stackoverflow.com/questions/61584852/input-ion-input-in-reactive-forms-problems-with-changedetectionstrategy

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