Requiring a checkbox to be checked

Question

I want a button to be disabled until a checkbox has been checked using a FormBuilder for Angular. I don't want to explicitly check the value of the checkbox and would prefer to use a validator so that I can simply check form.valid.

In both validation cases below the checkbox is

interface ValidationResult {
  [key:string]:boolean;
}

export class CheckboxValidator {
  static checked(control:Control) {
    return { "checked": control.value };
  }
}

@Component({
  selector: 'my-form',
  directives: [FORM_DIRECTIVES],
  template: `  <form [ngFormModel]="form" (ngSubmit)="onSubmit(form.value)">
    <input type="checkbox" id="cb" ngControl="cb">
    <button type="submit" [disabled]="!form.valid">
    </form>`
})

export class SomeForm {
  regForm: ControlGroup;

  constructor(fb: FormBuilder) {
    this.form = fb.group({
      cb: [ CheckboxValidator.checked ]
      //cb: [ false, Validators.required ] <-- I have also tried this
    });
  }

  onSubmit(value: any) {
    console.log('Submitted: ', this.form);
  }
}

Answer 1

.ts

@Component({
  selector: 'my-app', 
  template: `
    <h1>LOGIN</h1>
    <form [ngFormModel]="loginForm"  #fm="ngForm"  (submit)="doLogin($event)"> 

          <input type="checkbox" id="cb" ngControl="cb" #cb="ngForm" required>
          <button type="submit" [disabled]="!loginForm.valid">Log in</button>

          <br/>
              <div>Valid ={{cb.valid}}</div>
              <div>Pristine ={{cb.pristine}}</div>
              <div>Touch ={{cb.touched}}</div>
              <div>form.valid?={{loginForm.valid}}</div>
          <BR/>
          <BR/>

    </form>
    `,
  directives: [ROUTER_DIRECTIVES,FORM_DIRECTIVES,CORE_DIRECTIVES]
})

export class Login { 
  constructor(fb: FormBuilder) {
    this.loginForm = fb.group({
      cb: [false, Validators.required],
    //cb: ['',Validators.required] - this will also work.

    });
  }
  doLogin(event) {
    console.log(this.loginForm);
    event.preventDefault();
  }
}

Working Plunker.

Please let me know if any changes required.

Answer 2

You could just use a ValidatorPattern and check for the right (boolean) value:

<input type="checkbox" [formControl]="myForm.controls['isTosRead']">

and here is the binding:

this.myForm = builder.group({
        isTosRead: [false, Validators.pattern('true')]
    });

Answer 3

Since Angular 2.3.1 you can use Validators#requiredTrue:

Component:

this.formGroup = this.formBuilder.group({
  cb: [false, Validators.requiredTrue]
});

Template:

<form [formGroup]="formGroup">
  <label><input type="checkbox" formControlName="cb"> Accept it</label>
  <div style="color: red; padding-top: 0.2rem" *ngIf="formGroup.hasError('required', 'cb')">
    Required
  </div>
  <hr>
  <div>
    <button type="submit" [disabled]="formGroup.invalid">Submit</button>
  </div>
</form>

STACKBLITZ DEMO

Answer 4

I found that Validator.required does not work properly for checkboxes. If you check a checkbox and then uncheck it, the FormControl will still show it as valid, even though it is unchecked. I think it only checks that you set it to something, be it true or false.

Here is a quick simple validator you can add to your FormControl:

  mustBeChecked(control: FormControl): {[key: string]: string} {
    if (!control.value) {
      return {mustBeCheckedError: 'Must be checked'};
    } else {
      return null;
    }
  }

Answer 5

<h1>LOGIN</h1>
<form [formGroup]="signUpForm"> 
    <input type="checkbox" formControlName="cb">
    <button type="submit" [disabled]="!loginForm.valid" (click)="doLogin()">Log in</button>
</form>

export class Login { 
  public signUpForm: FormGroup;

  constructor(fb: FormBuilder) {
    this.signUpForm = fb.group({
      cb: [false, Validators.requiredTrue]
    });
  }
  doLogin() {

  }
}

Answer 6

I have this really simple example:

In your component:

login : FormGroup;

constructor(@Inject(FormBuilder)formBuilder : FormBuilder) {
this.login = formBuilder.group({userName: [null], password: [null],
staySignedIn: [false,Validators.pattern('true')]});
}

In your HTML:

<form [formGroup]="login" (ngSubmit)="onSubmit()">
    <div class="form-group">
        <input formControlName="userName" required>
    </div>
    <div class="form-group">
        <input formControlName="password" type="password" required>
    </div>
    <div>
        <label>
    <input formControlName="staySignedIn" checked="staySignedIn" type="checkbox"> bla
  </label>
    </div>
    <button type="submit">bla</button>
    <div >
        <a href>bla?</a>
    </div>
</form>

Answer 7

For Angular 8, I did it like the below for checking if atleast one checkbox is checked amongst three checkboxes

form = new FormGroup({
    // ...more form controls...
    myCheckboxGroup: new FormGroup({
      myCheckbox1: new FormControl(false),
      myCheckbox2: new FormControl(false),
      myCheckbox3: new FormControl(false),
    }, requireCheckboxesToBeCheckedValidator()),
    // ...more form controls...
  });

created a custom validator

import { FormGroup, ValidatorFn } from '@angular/forms';

export function requireCheckboxesToBeCheckedValidator(minRequired = 1): ValidatorFn {
  return function validate (formGroup: FormGroup) {
    let checked = 0;

    Object.keys(formGroup.controls).forEach(key => {
      const control = formGroup.controls[key];

      if (control.value === true) {
        checked ++;
      }
    });

    if (checked < minRequired) {
      return {
        requireCheckboxesToBeChecked: true,
      };
    }

    return null;
  };
}

and used it like below in html

<ng-container [formGroup]="form">
   <!-- ...more form controls... -->

   <div class="form-group" formGroupName="myCheckboxGroup">
      <div class="custom-control custom-checkbox">
        <input type="checkbox" class="custom-control-input" formControlName="myCheckbox1" id="myCheckbox1">
        <label class="custom-control-label" for="myCheckbox1">Check</label>
      </div>

      <div class="custom-control custom-checkbox">
        <input type="checkbox" class="custom-control-input" formControlName="myCheckbox2" id="myCheckbox2">
        <label class="custom-control-label" for="myCheckbox2">At least</label>
      </div>

      <div class="custom-control custom-checkbox">
        <input type="checkbox" class="custom-control-input" formControlName="myCheckbox3" id="myCheckbox3">
        <label class="custom-control-label" for="myCheckbox3">One</label>
      </div>

      <div class="invalid-feedback" *ngIf="form.controls['myCheckboxGroup'].errors && form.controls['myCheckboxGroup'].errors.requireCheckboxesToBeChecked">At least one checkbox is required to check</div>
    </div>

    <!-- ...more form controls... -->
  </ng-container>