binding data to angular checkbox

Question

I managed to bind the data from this.empDetails.services correctly on the UI, checkboxes are checked correctly, and also listed all the checkboxes options.

Answer 1

the "easy" way is to create a FormArray with values true/false. see the example in stackblitz

Update:Correct some errors

You fill the formArray using the data and the sservicesOptions

getFormArrayService(data:any[]):FormArray
  {
    //e.g. data=['mopping','washingclothes']
    // return a FormArray and the value will be [false,true,false,true]
    //if data=null, return a FormArray [false,false,false,false]
    return new FormArray(
       this.sservicesOptions.map(x=>new FormControl(data?data.find(dat=>dat==x.value)?true:false:false))
    )
  }

So, you can, in ngInit make some like

ngOnInit()
  {
    this.updateSvcForm=new FormGroup({
      sservices:this.getFormArrayService(null)
    })
  }

And in submitting the form, transform the value

  submit(updateSvcForm)
  {
      if (updateSvcForm.valid)
      {
          let services:string[]=[];
          updateSvcForm.value.sservices.forEach((x,index)=>
          {
              if (x)
                 services.push(this.sservicesOptions.value)
          })
          const result={
              ...updateSvcForm.value, //all value of the form but
              sservices:services
          }
          console.log(result)
      }
  }

The .html becomes like

<form *ngIf="updateSvcForm" [formGroup]="updateSvcForm" (submit)="submit(updateSvcForm)">
    <div formArrayName="sservices">
      <div *ngFor="let control of updateSvcForm.get('sservices').controls;let i=index">
        <input type="checkbox" [formControlName]="i"/>
        {{sservicesOptions[i].description}}

        </div>
      </div>
      <button type="submit">submit</button>
    </form>
    {{updateSvcForm?.value|json}}

The "not so easy way" a customFormControl, see an example in stackblitz

Basically, we create a series of the checkbox, each change in checkbox return the "booleansToProp". In the example, I add a property "required", then indicate it is invalid if no check is checked and isString if we can return a string, not an array

@Component({
  selector: 'check-box-group',
  template: `
      <ng-container *ngFor="let item of source;let i=index;let last=last">

      <div  [ngClass]="last?'form-group':''" class="form-check" >
         <input type="checkbox" class="form-check-input"  id="{{_name+''+i}}"
              [ngModel]="_selectedItems[i]"
             (ngModelChange)="setValue($event,i)" (blur)="onTouched()" >
         <label class="form-check-label" for="{{_name+''+i}}">{{item[_col]}}</label>
      </div>

      </ng-container>
  `,
  providers: [
    {
      provide: NG_VALUE_ACCESSOR,
      useExisting: forwardRef(() => CheckBoxGroupComponent),
      multi: true
    },
    {
      provide: NG_VALIDATORS,
      useExisting: forwardRef(() => CheckBoxGroupComponent),
      multi: true,
    }

  ],
  styles:[`
    .focused {
       outline: black dotted thin;
    }`
  ]
})
export class CheckBoxGroupComponent implements ControlValueAccessor {

  @Input() 
  set source(value)
  {
    this._source=value;
    //we need to know which column has the "value" and which column has the "text"
    //replace all extrange character else ":" and ","
    let aux=JSON.stringify(value[0]).replace(/[^\w|:|,\s]/gi, '').split(',');
    this._key=aux[0].split(':')[0]
    this._col=aux[1].split(':')[0]
  }
  get source()
  {
    return this._source;
  }

  _selectedItems: any[] = [];
  _source;
  _key: string;
  _col: string;
  _name:string="";
  _isString:boolean=false;
  _isRequired:boolean=false;
  onChange;
  onTouched;

  constructor(el:ElementRef) { 
    let name=el.nativeElement.getAttribute('name');
    //we store in this._isRequired if the element has an attribute "required"       
     this._isRequired=el.nativeElement.getAttribute('isRequired')!=null?true:false;
    //idem if the element has an attribute "isString" 

    this._isString=el.nativeElement.getAttribute('isString')!=null?true:false;
    //Is necesary give a name to the control if there're severals check-box-group
    this._name=name?name:"ck";

    }
  writeValue(value: any[]|any): void {
    this._selectedItems = this._isString?
       this.propsToBoolean(value?value.split(','):""):this.propsToBoolean(value);
  }

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

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

  setDisabledState(isDisabled: boolean): void {
  }
  //setValue is called each time you check/uncheck a checkbox
  //Simple call to this.onChange with the value o the result of the
  //function this.booleanToProps
  setValue(value: boolean, index: number) {
    this._selectedItems[index] = value;
    this.onChange(this._isString?
         this.booleanToProps(this._selectedItems).join(','):
         this.booleanToProps(this._selectedItems));

  }

  validate(control: AbstractControl): ValidationErrors | null{
    if (!this._isRequired)
      return null;
    if (!this._selectedItems.find(x=>x))
      return {error:"you must select one option at last"}

    return null
  }

  //we received an array (or a string separated by commas) and
  //return an array of true/false
  propsToBoolean(props): any[] {
    let propsString=props?props.map(x=>''+x):null;
    return props ? this.source.map((x: any) => propsString.indexOf(''+x[this._key]) >= 0)
      : this.source.map(x => false);

  }

  //we received an array of true/false and return an array with the values
  //or with teh values separated by commas
  booleanToProps(propsBoolean: boolean[]) {
    let props: any[] = [];
    if (propsBoolean) {
      propsBoolean.forEach((item, index) => {
        if (item)
          props.push(this.source[index][this._key])
      })
    }
    return props;

  }

}

Answer 2

The reason for this, is that you are using checked to mark which checkboxes should be checked, they have no correlation to your form array, so if you do not touch the checkboxes, the formarray will correctly be empty.

I can come up with a couple options to solve this... also the following changes:

change function could be changed to this:

onCheckChange(event) {
  if (event.target.checked) {
    this.ssArray.push(this.fb.control(event.target.value));
  }
  else {
   this.ssArray.removeAt(this.ssArray.value.findIndex(x => x === event.target.value))
  }
}

Doesn't matter how you do it, your way works as well :) I also like using FormBuilder (here injected as fb).

I like to use a getter in this case:

get ssArray() {
  return this.updateSvcForm.get('sservices') as FormArray;
}

The options I can think of:

1. add a checked property to the objects in your array sservicesOptions
2. Keep your isSelected function, but add the chosen options to your formarray initially

---

I like option 1 best, so add a checked property to the objects:

servicesOptions = [
  { description: '1. Sweeping', value: 'sweeping', checked: false },
  { description: '2. Mopping', value: 'mopping', checked: false },
  { description: '3. Windows', value: 'windows', checked: false },
  { description: '4. Washing Clothes', value: 'washingclothes', checked: false },
];

Then when you build the form, change the checked status for those that should be preselected, and also add the values that should be checked to your form array:

constructor(private fb: FormBuilder) {
  this.updateSvcForm = this.fb.group({
    sservices: this.fb.array([]),
  });
  // change the checked status for the checkboxes that should be checked
  this.servicesOptions.map(x => 
    this.empDetails.services.indexOf(x) >= 0 ? x.checked = true : x.checked = false)
  // initially set the selected form controls to the formarray
  this.empDetails.services.map((x) => this.ssArray.push(this.fb.control(x)))
}

Then you can add [checked]="service.checked" in template.

DEMO

---

Option 2:

Keep your checked function like you have, just remember to add the prechosen values to your formarray. I don't really like this option, since for example, we end up calling a function in template, which is really not recommended. But anyway, keep the code as the same as you have now, just add the intial values to the formarray:

this.updateSvcForm = this.fb.group({
  sservices: this.fb.array([]),
});
// add the intial values to the formarray:
this.empDetails.services.map((x) => this.ssArray.push(this.fb.control(x)))

DEMO

I added a console.log inside the function, to show how it is called. It's okay for a demo like this, but if you have a big form, I would really caution for you to use this solution.

---

There would be a third option, to actually set all values to your form array, and then just toggle the boolean value of the checkbox, but that would require some refactoring of code, which I don't know if you want. But there is that option too.

Answer 3

you forget to set the new value of the form Array sservices :

onCheckChange(event) {
  const sservicesFormArray: FormArray =
    this.updateSvcForm.get('sservices') as FormArray;


  if (event.target.checked) {
    sservicesFormArray.push(new FormControl(event.target.value));
  }
  else {
    let i: number = 0;
    sservicesFormArray.controls.forEach((ctrl: FormControl) => {
      if (ctrl.value == event.target.value) {
        sservicesFormArray.removeAt(i);
        break;
      }
      i++;
    });
  }
  // set the new value of sservices form array
  this.updateSvcForm.setControl('sservices', sservicesFormArray);
}