Ways of modifying the readonly and required attributes of an HTML element using Angular2 Typescript

Question

Ways of modifying the readonly and required attributes of an HTML element using Angular2 Typescript

I am facing an issue with changing input field attributes back and forth in some of my components. I have a code that successfully changes the readonly attribute as needed. However, when trying to change the required attribute, Angular2 still considers the fieldCtrl valid even after making the change.

You can see the problem illustrated in this Plunker: https://plnkr.co/edit/Yq2RDzUJjLPgReIgSBAO?p=preview

//our root app component
import {Component} from 'angular2/core'

@Component({
  selector: 'my-app',
  providers: [],
  template: `
    <div>
    <form #f="ngForm">
      <button type="button" (click)="toggleReadOnly()">Change readonly!</button>
      <button type="button" (click)="toggleRequired()">Change required!</button>
      <input id="field" [(ngModel)]="field" ngControl="fieldCtrl" #fieldCtrl="ngForm"/>
      {{fieldCtrl.valid}}
    </form>
    </div>
  `,
  directives: []
})
export class App {
  constructor() {
    this.name = 'Angular2'
  }

  toggleRequired(){
    this.isRequired = !this.isRequired;
    var fieldElement = <HTMLInputElement>document.getElementById('field');
    if (this.isRequired){
      fieldElement.required = true;
      this.field = "it's required now";
    }
    else{
      fieldElement.required = false;
      this.field = "can leave it blank";
    }
  }

  toggleReadOnly(){
    this.isReadOnly = !this.isReadOnly;
    var fieldElement = <HTMLInputElement>document.getElementById('field');
    if (this.isReadOnly){
      fieldElement.readOnly = true;
      this.field = "it's readonly now";
    }
    else{
      fieldElement.readOnly = false;
      this.field = "feel free to edit";
    }
  }

  private isReadOnly:boolean=false;

  private field:string = "feel free to edit";

  private isRequired:boolean=false;

}

I have tried suggested method

[required]="isRequired" [readonly]="isReadOnly"

This works well for readonly and for required=true. However, I am unable to turn off the required attribute anymore, as it shows the empty field is invalid even though it's not required.

Updated Plunker here: https://plnkr.co/edit/6LvMqFzXHaLlV8fHbdOE

I also attempted the following method

[required]="isRequired ? true : null"

Although this method successfully adds/removes the required attribute as needed, the field controller's valid property still shows false for an empty field that is not required.

Can someone advise on the correct way to change the required attribute in Angular2 Typescript?

typescript angular

Answer 1

Answer №1

In order to remove bound attributes, they must be set to null. There was a conversation about changing this to remove on false, but it was ultimately rejected, at least for the time being.

 [required]="isRequired ? '' : null"

or

 [required]="isRequired ? 'required' : null"

Your Plunker is showing an error due to missing [] around ngControl.

For a functional example, check out this Plunker link

Be sure to also read Deilan's comments below for additional insight.

Answer 2

In order to remove bound attributes, they must be set to null. There was a conversation about changing this to remove on false, but it was ultimately rejected, at least for the time being.

 [required]="isRequired ? '' : null"

or

 [required]="isRequired ? 'required' : null"

Your Plunker is showing an error due to missing [] around ngControl.

For a functional example, check out this Plunker link

Be sure to also read Deilan's comments below for additional insight.

Answer 3

Answer №2

If you’re looking for a solution to manage the enabled/disabled state of validators, I recommend creating a service that can handle this functionality. By utilizing this service, you can easily bind your validation controls and keep track of their states.

Validator State Management

The StateValidator class plays a crucial role in managing the validator's state - whether it’s enabled or disabled.

export class StateValidator {
    public enabled: boolean = true;
    validator: (control: Control) => { [key: string]: boolean };
    constructor(validator: (control: Control) => 
        { [key: string]: boolean }, enabled: boolean) {
        this.enabled = enabled;
        this.validator = validator;

    }

    enable() {
        this.enabled = true;
    }
    disable() {
        this.enabled = false;
    }
    toggle() {
        this.enabled = !this.enabled;
    }
    get() {
        return (control: Control) => {
            if (this.enabled)
                return this.validator(control);
            return null;
        }
    }
}

This class offers methods like enabling, disabling, and toggling the validator. It also provides a get method which returns a new validator function based on its current state.

Validation Service Singleton

The ValidationService class serves as a singleton service responsible for registering validators by key and supporting functionalities to manipulate their states accordingly.

export class ValidationService {
    ...
}

The ValidationService includes functions like register, enable, disable, toggle, and list to effectively manage the validators and their status.

Usage in Components

To integrate the ValidationService, ensure it is registered with the appropriate injector either at root level or component level.

@Component({
  selector: 'app',
  providers: [ValidationService],
  ...
})

After registration, inject the service into your component and use it to register and handle the state of validators within your forms.

this.form = new ControlGroup({
    name: new Control('hello',
        Validators.compose([
            validationService.register('required', Validators.required),
            validationService.register('minlength', Validators.minLength(4)),
            Validators.maxLength(10)]))

});

Advanced Functionality

Toggle between validator states using the service, and even combine different validators for more complex form validations.

validationService.toggle('required');

Additionally, you can display a list of validators in a table and interactively toggle their states via button clicks.

<table>
  <tr>
     <td>Validator</td>
     <td>Is Enabled?</td>
     <td></td>
  </tr>
  <tr *ngFor="#v of validationService.list()">
     <td>{{v.key}}</td>
     <td>{{v.value }}</td>
     <td><button (click)="validationService.toggle(v.key)">Toggle</button></td>
  </tr>
</table>

For a demonstration of this solution, check out the provided Plnkr and image links.

Answer 4

If you’re looking for a solution to manage the enabled/disabled state of validators, I recommend creating a service that can handle this functionality. By utilizing this service, you can easily bind your validation controls and keep track of their states.

Validator State Management

The StateValidator class plays a crucial role in managing the validator's state - whether it’s enabled or disabled.

export class StateValidator {
    public enabled: boolean = true;
    validator: (control: Control) => { [key: string]: boolean };
    constructor(validator: (control: Control) => 
        { [key: string]: boolean }, enabled: boolean) {
        this.enabled = enabled;
        this.validator = validator;

    }

    enable() {
        this.enabled = true;
    }
    disable() {
        this.enabled = false;
    }
    toggle() {
        this.enabled = !this.enabled;
    }
    get() {
        return (control: Control) => {
            if (this.enabled)
                return this.validator(control);
            return null;
        }
    }
}

This class offers methods like enabling, disabling, and toggling the validator. It also provides a get method which returns a new validator function based on its current state.

Validation Service Singleton

The ValidationService class serves as a singleton service responsible for registering validators by key and supporting functionalities to manipulate their states accordingly.

export class ValidationService {
    ...
}

The ValidationService includes functions like register, enable, disable, toggle, and list to effectively manage the validators and their status.

Usage in Components

To integrate the ValidationService, ensure it is registered with the appropriate injector either at root level or component level.

@Component({
  selector: 'app',
  providers: [ValidationService],
  ...
})

After registration, inject the service into your component and use it to register and handle the state of validators within your forms.

this.form = new ControlGroup({
    name: new Control('hello',
        Validators.compose([
            validationService.register('required', Validators.required),
            validationService.register('minlength', Validators.minLength(4)),
            Validators.maxLength(10)]))

});

Advanced Functionality

Toggle between validator states using the service, and even combine different validators for more complex form validations.

validationService.toggle('required');

Additionally, you can display a list of validators in a table and interactively toggle their states via button clicks.

<table>
  <tr>
     <td>Validator</td>
     <td>Is Enabled?</td>
     <td></td>
  </tr>
  <tr *ngFor="#v of validationService.list()">
     <td>{{v.key}}</td>
     <td>{{v.value }}</td>
     <td><button (click)="validationService.toggle(v.key)">Toggle</button></td>
  </tr>
</table>

For a demonstration of this solution, check out the provided Plnkr and image links.

Answer 5

Answer №3

Here's another approach that I like to use:

import {Directive, ElementRef, Input} from '@angular/core';

@Directive({
    selector: '[toggleRequired]'
})
export class ToggleRequiredDirective {
    @Input() public set toggleRequired(condition: boolean) {
        if (condition) {
            (<HTMLElement>this.element.nativeElement).setAttribute('required', 'true');
        } else {
            (<HTMLElement>this.element.nativeElement).removeAttribute("required");
        }
    } 

    constructor(
        private element: ElementRef
    ) { } 
}

To either add or remove the required attribute, simply apply this directive to an HTML element:

<input [toggleRequired]='flagPropertyOfYourComponent'>

Answer 6

Here's another approach that I like to use:

import {Directive, ElementRef, Input} from '@angular/core';

@Directive({
    selector: '[toggleRequired]'
})
export class ToggleRequiredDirective {
    @Input() public set toggleRequired(condition: boolean) {
        if (condition) {
            (<HTMLElement>this.element.nativeElement).setAttribute('required', 'true');
        } else {
            (<HTMLElement>this.element.nativeElement).removeAttribute("required");
        }
    } 

    constructor(
        private element: ElementRef
    ) { } 
}

To either add or remove the required attribute, simply apply this directive to an HTML element:

<input [toggleRequired]='flagPropertyOfYourComponent'>

Ways of modifying the readonly and required attributes of an HTML element using Angular2 Typescript

Answer №1

Answer №2

Validator State Management

Validation Service Singleton

Usage in Components

Advanced Functionality

Answer №3

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