How to trigger change() in a angular form by a custom control without an input

Question

I do want to create a custom control which does not include any input. Whenever the control changes, I do want to save the complete form.

Our current approach uses the form-changed-event like this:

 <form #demoForm="ngForm" (change)="onChange()">
      <custom-input name="someValue" [(ngModel)]="dataModel">
      </custom-input>
 </form>

As you can see, we use the "change"-event to react to any change in the form. This works fine as long as we have inputs, checkboxes, ... as controls.

But our custom control does only exist out of a simple div we can click on. Whenever I click on the div the value of the control is increased by 1. But the "change"-event of the form is not fired. Do I somehow have to link my custom control to the form? Or are there any events which need to be fired?

import { Component, forwardRef } from '@angular/core';
import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms';

@Component({
    selector: 'custom-input',
    template: `<div (click)="update()">Click</div>`,
    providers: [{
        provide: NG_VALUE_ACCESSOR,
        useExisting: forwardRef(() => CustomInputComponent),
        multi: true
    }]
})
export class CustomInputComponent implements ControlValueAccessor {

    private onTouchedCallback: () => void = () => {};
    private onChangeCallback: (_: any) => void = () => {};

    update(){
      this.value++;
    }

    get value(): any {
        return this.innerValue;
    };

    set value(v: any) {
        console.log("Change to");
        if (v !== this.innerValue) {
            this.innerValue = v;
            this.onChangeCallback(v);
        }
    }

    writeValue(value: any) {
        if (value !== this.innerValue) {
            this.innerValue = value;
        }
    }

    registerOnChange(fn: any) {
        this.onChangeCallback = fn;
    }

    registerOnTouched(fn: any) {
        this.onTouchedCallback = fn;
    }
}

I've created a plunker to demonstrate the problem: https://plnkr.co/edit/ushMfJfcmIlfP2U1EW6A

Whenever you click on "Click" the model-value is increased, but there is no output on the console, as the change-event is not fired... (There is a console.log linked to the change-event)

Please pay attention to the tag excerpts that show when you're adding tags. angularjs is for AngularJS 1.x. angular2 is for Angular 2+. — Heretic Monkey
– Heretic Monkey, Commented Feb 21, 2017 at 16:52
HTML5 forms have a very specific defined list of elements that are considered to be part of the form tree; elements not on this list, including div, span, table, and others, including custom elements, will not be handled as part of the HTML5 form. you might be able to accomplish this if your component used output rather than div for it's template, but that may not work as you expect either. Basically, this isn't built into the spec. — Claies
– Claies, Commented Feb 21, 2017 at 16:55

Stefan · Accepted Answer · 2017-02-28 08:44:26Z

Thanks for your replies.

Finally I found the following solution to this problem: As Claies mentioned in the comment, my custom component does not fire the change event. Therfore the form does never know about the change. This has nothing todo with angular, but as said is the expected behaviour of a input/form.

The easiest solution is to fire the change-event in the customcontrol when a change happens:

constructor(private element: ElementRef, private renderer: Renderer) {
}

public triggerChanged(){
    let event = new CustomEvent('change', {bubbles: true});
    this.renderer.invokeElementMethod(this.element.nativeElement, 'dispatchEvent', [event]);
}

That's it, whenever I called "onControlChange(..)" in my custom component, then I fire this event afterward.

Be aware, that you need the Custom-Event-Polyfill to support IE! https://www.npmjs.com/package/custom-event-polyfill

Stephen Paul · Accepted Answer · 2020-03-16 09:30:33Z

2

Thanks Stefan for pointing me in the right direction.

Unfortuantely Renderer (which has invokeElementMethod()) has recently been deprecated in favor or Renderer2 (which does not have that method)

So the following worked for me

this.elementRef.nativeElement.dispatchEvent(new CustomEvent('change', { bubbles: true }));

answered Mar 16, 2020 at 9:30

Stephen Paul

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2 Comments

Rohit Kumar Over a year ago

Stefan with an F helped Stephen with a ph

Patrick Prakash Over a year ago

@RameshSharmaYadav lol. Nice finding!

amansoni211 · Accepted Answer · 2017-02-21 16:47:00Z

1

You need to emit the click event of div to its parent. so that you can handle the event.

Plunker Link

Parent component:

import { Component, forwardRef, Output, EventEmitter } from '@angular/core'; // add output and eventEmitter
import { NG_VALUE_ACCESSOR, ControlValueAccessor } from '@angular/forms';

@Component({
 selector: 'custom-input',
 template: `<div (click)="update($event)">Click</div>`,
 providers: [{
 provide: NG_VALUE_ACCESSOR,
 useExisting: forwardRef(() => CustomInputComponent),
 multi: true
}]
})

export class CustomInputComponent implements ControlValueAccessor {

  private onTouchedCallback: () => void = () => {};
  private onChangeCallback: (_: any) => void = () => {};
  @Output() clickEvent = new EventEmitter(); // add this

  update(event){
    this.value++;
    this.clickEvent.emit(event); // emit the event on click event
  }

  get value(): any {
      return this.innerValue;
  };
}

child component:

//our root app component
import {Component} from '@angular/core'

@Component({
    selector: 'demo-app',
    template: `
        <p><span class="boldspan">Model data:</span> {{dataModel}}</p>
        <form #demoForm="ngForm">
          <custom-input name="someValue" 
                      [(ngModel)]="dataModel" (clickEvent) = onChange()> // handling emitted event here
            Write in this wrapper control:
          </custom-input>
        </form>`
})
export class AppComponent {
    dataModel: string = '';

    public onChange(){
      console.log("onChangeCalled");
    }
}

edited Feb 21, 2017 at 16:47

answered Feb 21, 2017 at 16:39

amansoni211

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2 Comments

Stefan Over a year ago

This would work, but in a form with 20 controls I would end up with 20 clickEvent-registrations. The cool thing about the form-change-event is, that I do only have a single entry point. So it would be nice to somhow tlee the form that the value of the custom component has changed.

amansoni211 Over a year ago

@Stefan I can not think of any other solution to this problem. according to me, to detect any change in child component, eventemitter would be the possible solution. :)

proxeld · Accepted Answer · 2019-06-07 14:09:40Z

0

It seems that change event is not fired on form when you call ControlValueAccessor onChange callback (callback passed in registerOnChange function), but valueChanges observable (on the whole form) is triggered.

Instead of:

 ...
 <form (change)="onChange()">
 ...

you can try to use:

this.form.valueChanges
  .subscribe((formValues) => {
    ...
  });

Of course, you must get proper form reference in your component.

answered Jun 7, 2019 at 14:09

proxeld

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