Using Mat-Error for Two Way Binding leads to frequent triggering of ngModelChange事件

Question

Using Mat-Error for Two Way Binding leads to frequent triggering of ngModelChange事件

I am working with a mat input field that has two-way data binding using ngModel, and I want to add validation using mat-error and formControl.

<mat-form-field [formGroup]="myForm">
  <input matInput formControlName="myFormName" autocomplete="off" 
         (ngModelChange)="dataChanged(myValue)" [ngModel]="myValue">
  <mat-error>
    Error! Value must be between <strong>{{minVal}}</strong>
    and <strong>{{maxVal}}</strong>.
  </mat-error>
</mat-form-field>

However, I am facing an issue where ngModelChange is triggered multiple times during initialization when the ngModel value myValue is set from HTTP calls in a service. It seems like there may be a conflict between template-driven and reactive forms.

My goal is to bind data two ways to the input while also displaying mat-errors without unnecessary ngModelChange events triggered when the input is populated with data on initialization.

html angular typescript

Answer 1

Answer №1

The form structure in your Angular project might resemble the following layout:

import { Component } from "@angular/core";
import {
  FormGroup,
  FormControl,
  Validators
} from "@angular/forms";

/** @title Custom ErrorStateMatcher Input */
@Component({
  selector: "input-error-state-matcher-example",
  templateUrl: "./input-error-state-matcher-example.html",
  styleUrls: ["./input-error-state-matcher-example.css"]
})
export class InputErrorStateMatcherExample {
  minVal = 10;
  maxVal = 25;

  myForm = new FormGroup({
    myFormName: new FormControl("", [
      Validators.minLength(this.minVal),
      Validators.maxLength(this.maxVal)
    ])
  });
}

In this code snippet, the minLength and maxLength validators have been set up.

Furthermore, the binding between the form and template is established using [formGroup] and formControlName directives.

Angular will handle all validations for you seamlessly.

To retrieve errors, simply access the errors property on myForm.controls['myFormName'] like so:

<mat-form-field [formGroup]="myForm">
    <input matInput formControlName="myFormName" autocomplete="off">
    <mat-error *ngIf="myForm.controls['myFormName'].errors">
        Error! Value must be between <strong>{{minVal}}</strong>
        and <strong>{{maxVal}}</strong>.
    </mat-error>
</mat-form-field>

For reference, check out this Live Demo.

Answer 2

The form structure in your Angular project might resemble the following layout:

import { Component } from "@angular/core";
import {
  FormGroup,
  FormControl,
  Validators
} from "@angular/forms";

/** @title Custom ErrorStateMatcher Input */
@Component({
  selector: "input-error-state-matcher-example",
  templateUrl: "./input-error-state-matcher-example.html",
  styleUrls: ["./input-error-state-matcher-example.css"]
})
export class InputErrorStateMatcherExample {
  minVal = 10;
  maxVal = 25;

  myForm = new FormGroup({
    myFormName: new FormControl("", [
      Validators.minLength(this.minVal),
      Validators.maxLength(this.maxVal)
    ])
  });
}

In this code snippet, the minLength and maxLength validators have been set up.

Furthermore, the binding between the form and template is established using [formGroup] and formControlName directives.

Angular will handle all validations for you seamlessly.

To retrieve errors, simply access the errors property on myForm.controls['myFormName'] like so:

<mat-form-field [formGroup]="myForm">
    <input matInput formControlName="myFormName" autocomplete="off">
    <mat-error *ngIf="myForm.controls['myFormName'].errors">
        Error! Value must be between <strong>{{minVal}}</strong>
        and <strong>{{maxVal}}</strong>.
    </mat-error>
</mat-form-field>

For reference, check out this Live Demo.

Using Mat-Error for Two Way Binding leads to frequent triggering of ngModelChange事件

Answer №1

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