Mastering checkbox selection in Angular reactive formsLearn how to effortlessly manage the checked status of

Question

Mastering checkbox selection in Angular reactive formsLearn how to effortlessly manage the checked status of

I am struggling with setting the checked status of a checkbox control within an Angular reactive form.

My goal is to change the value based on the checked status, but it seems like the value is controlling the status instead.

For instance, I want the formControl to be 'Man' when the checkbox is checked and 'Woman' when it is not. However, both values result in the checkbox being always checked.

I tried using the [checked] attribute, but realized that the main model is taking control over the input state.

  <input class="form-check-input" type="checkbox"
        [id]="field.key"
        [formControlName]="field.key" 
        [checked]="formControl.value === 'Man'" (change)="onCheckChange($event)">


  onCheckChange($event: any) {
    let val = $event.target.checked ? 'Man' : 'Woman';
    this.formControl.patchValue(val);
  }

Is there a way to make this functionality work as intended?

angular angular-reactive-forms

Answer 1

Answer №1

A checkbox can only have a true or false value, it cannot be a string.

If you want to convert it into a string, there are a couple of ways to do so:

Define the checkbox outside of your form group and update a field within the form group:

form = this.formBuilder.group({
  sex: ''
});

sexControl = new FormControl(true);

ngOnInit() {
  // Make sure to handle memory leaks properly
  this.sexControl.valueChanges.subscribe(val => {
    const sex = val ? 'Male' : 'Female';
    this.form.patchValue({ sex });
  });
}

Modify the value when submitting the form:

  onSubmit() {
    const { sex, ...value } = this.form.value;
    value.sex = sex ? 'Male' : 'Female';
  }

Answer 2

A checkbox can only have a true or false value, it cannot be a string.

If you want to convert it into a string, there are a couple of ways to do so:

Define the checkbox outside of your form group and update a field within the form group:

form = this.formBuilder.group({
  sex: ''
});

sexControl = new FormControl(true);

ngOnInit() {
  // Make sure to handle memory leaks properly
  this.sexControl.valueChanges.subscribe(val => {
    const sex = val ? 'Male' : 'Female';
    this.form.patchValue({ sex });
  });
}

Modify the value when submitting the form:

  onSubmit() {
    const { sex, ...value } = this.form.value;
    value.sex = sex ? 'Male' : 'Female';
  }

Answer 3

Answer №2

Wouldn't it make more sense to use radio buttons in this scenario?

  <input class="form-check-input" type="radio"
        [id]="field.key"
        [formControlName]="field.key" 
        value="Men" />

  <input class="form-check-input" type="radio"
        [id]="field.key"
        [formControlName]="field.key" 
        value="Female" />

If using radio buttons is not feasible, you may need to create a custom form control to manage this behavior. The implementation would typically involve a combination of the writeValue and onChange methods to determine the value to be set.

const CHECKBOX_VALUE_ACCESSOR: Provider = {
  provide: NG_VALUE_ACCESSOR,
  useExisting: forwardRef(() => MyCheckboxControlValueAccessor),
  multi: true,
};

@Directive({
  selector:
      'input[type=checkbox][formControlName],input[type=checkbox][formControl],input[type=checkbox][ngModel]',
  host: {'(change)': 'updateValue($event.target.checked)', '(blur)': 'onTouched()'},
  providers: [CHECKBOX_VALUE_ACCESSOR]
})
export class MyCheckboxControlValueAccessor implements ControlValueAccessor {

  onChange = (_: any) => {};

  onTouched = () => {};

  constructor(private _renderer: Renderer2, private _elementRef: ElementRef) {
  }

  protected setProperty(key: string, value: any): void {
    this._renderer.setProperty(this._elementRef.nativeElement, key, value);
  }

  registerOnTouched(fn: () => void): void {
    this.onTouched = fn;
  }

  registerOnChange(fn: (_: any) => {}): void {
    this.onChange = fn;
  }
  
  setDisabledState(isDisabled: boolean): void {
    this.setProperty('disabled', isDisabled);
  }
  
  updateValue(value: any) {
    const valueToUpdate = (value === true) ? 'Male': 'Female';
    this.onChange(valueToUpdate);
  }
  
  writeValue(value: string) {
    this.updateValue(value);
  }
}

HTML

  <input
    type="checkbox"
    myCheckbox
    #cb
    formControlName="sex"
  />

Answer 4

Wouldn't it make more sense to use radio buttons in this scenario?

  <input class="form-check-input" type="radio"
        [id]="field.key"
        [formControlName]="field.key" 
        value="Men" />

  <input class="form-check-input" type="radio"
        [id]="field.key"
        [formControlName]="field.key" 
        value="Female" />

If using radio buttons is not feasible, you may need to create a custom form control to manage this behavior. The implementation would typically involve a combination of the writeValue and onChange methods to determine the value to be set.

const CHECKBOX_VALUE_ACCESSOR: Provider = {
  provide: NG_VALUE_ACCESSOR,
  useExisting: forwardRef(() => MyCheckboxControlValueAccessor),
  multi: true,
};

@Directive({
  selector:
      'input[type=checkbox][formControlName],input[type=checkbox][formControl],input[type=checkbox][ngModel]',
  host: {'(change)': 'updateValue($event.target.checked)', '(blur)': 'onTouched()'},
  providers: [CHECKBOX_VALUE_ACCESSOR]
})
export class MyCheckboxControlValueAccessor implements ControlValueAccessor {

  onChange = (_: any) => {};

  onTouched = () => {};

  constructor(private _renderer: Renderer2, private _elementRef: ElementRef) {
  }

  protected setProperty(key: string, value: any): void {
    this._renderer.setProperty(this._elementRef.nativeElement, key, value);
  }

  registerOnTouched(fn: () => void): void {
    this.onTouched = fn;
  }

  registerOnChange(fn: (_: any) => {}): void {
    this.onChange = fn;
  }
  
  setDisabledState(isDisabled: boolean): void {
    this.setProperty('disabled', isDisabled);
  }
  
  updateValue(value: any) {
    const valueToUpdate = (value === true) ? 'Male': 'Female';
    this.onChange(valueToUpdate);
  }
  
  writeValue(value: string) {
    this.updateValue(value);
  }
}

HTML

  <input
    type="checkbox"
    myCheckbox
    #cb
    formControlName="sex"
  />

Answer 5

Answer №3

One way to prevent the View from being updated when a checkbox is unchecked is by passing a second configuration option to patchValue. By setting emitModelToViewChange: false, we can achieve this.

onCheckChange($event: any) {
    const val = $event.target.checked ? 'Man' : 'Woman';
    if (val === 'Man') {
      this.field.patchValue(val);
    } else {
      this.field.patchValue(val, { emitModelToViewChange: false });
    }
  }

Take a look at this example

Answer 6

One way to prevent the View from being updated when a checkbox is unchecked is by passing a second configuration option to patchValue. By setting emitModelToViewChange: false, we can achieve this.

onCheckChange($event: any) {
    const val = $event.target.checked ? 'Man' : 'Woman';
    if (val === 'Man') {
      this.field.patchValue(val);
    } else {
      this.field.patchValue(val, { emitModelToViewChange: false });
    }
  }

Take a look at this example

Answer 7

Answer №4

It's actually quite simple, similar to this example in the Stack Overflow post

<input class="form-check-input" type="checkbox"
        [ngModel]="this.form.get(field.key).value=='Man'"
        (ngModelChange)="this.form.get(field.key).setValue($even?'Man':'Woman')"
        [ngModelOptions]="{standalone:true}"
</input>

The field "key" does not use formControlName. Instead, we can utilize [ngModel] to modify a FormControl. Keep in mind that a FormControl always exists (it doesn't necessarily have to be tied to an input with formControl)

Answer 8

It's actually quite simple, similar to this example in the Stack Overflow post

<input class="form-check-input" type="checkbox"
        [ngModel]="this.form.get(field.key).value=='Man'"
        (ngModelChange)="this.form.get(field.key).setValue($even?'Man':'Woman')"
        [ngModelOptions]="{standalone:true}"
</input>

The field "key" does not use formControlName. Instead, we can utilize [ngModel] to modify a FormControl. Keep in mind that a FormControl always exists (it doesn't necessarily have to be tied to an input with formControl)

Answer 9

Answer №5

My approach involved disconnecting the input from the formControl and adding some event listeners

<input class="form-check-input" type="checkbox" [disabled]="formControl.disabled"
[id]="field.key" 
[checked]="field.value === 'True'" 
(change)="onCheckChange($event)">

This method led to a few minor issues, but it served my purpose effectively.

Generally speaking, I do not recommend such solutions.

I reevaluated the entire concept and ultimately decided to pass boolean values and then transform them after submission. Thank you for your assistance!

Answer 10

My approach involved disconnecting the input from the formControl and adding some event listeners

<input class="form-check-input" type="checkbox" [disabled]="formControl.disabled"
[id]="field.key" 
[checked]="field.value === 'True'" 
(change)="onCheckChange($event)">

This method led to a few minor issues, but it served my purpose effectively.

Generally speaking, I do not recommend such solutions.

I reevaluated the entire concept and ultimately decided to pass boolean values and then transform them after submission. Thank you for your assistance!

Mastering checkbox selection in Angular reactive formsLearn how to effortlessly manage the checked status of

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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