How to set and get form values when we use css dropdown as shared component

Question

I have a shared component which is a html and css dropdown. I am calling this shared component from a parent component with different data.

For example I have 3 instances of shared component from parent component, so parent form group will have 3 formControls. Since all the 3 formcontrols are now a shared component. How to set and get selected data from all the 3 dropdowns.

Also if any default item is to be set for any dropdown, how can we achieve it.

Main objective here is to access/get all the formControlName values in parent component form group.

I have attached demo code https://stackblitz.com/edit/angular-mncdy5 Please help as I am in a learning stage!

Answer 1

You need to implement ControlValueAccessors in the shared component so you can attach formControls to them in parent component. Here is a great article on that its preety straight forward.

https://medium.com/@majdasab/implementing-control-value-accessor-in-angular-1b89f2f84ebf

This is how your customDropdown component needs to look to implement ControlValueAccessors

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

@Component({
  selector: 'app-common-dropdown',
  templateUrl: './common-dropdown.component.html',
  styleUrls: ['./common-dropdown.component.css'],
  providers: [     
      {       provide: NG_VALUE_ACCESSOR, 
              useExisting: forwardRef(() => CommonDropdownComponent),
              multi: true     
      }
    ] 
})
export class CommonDropdownComponent implements ControlValueAccessor {

  @Input() placeHolder: string;
  @Input() dropDownId: string;
  @Input() dataList: any;

  onChange: any = () => {}
  onTouch: any = () => {}
  val= "" // this is the updated value that the class accesses

  set value(val){  // this value is updated by programmatic changes if( val !== undefined && this.val !== val){
    this.val = val
    this.onChange(val)
    this.onTouch(val)
  }


  constructor() { }

  ngOnInit() {
  }

  // this method sets the value programmatically
  writeValue(value: any){ 
    this.value = value
  }
  registerOnChange(fn: any){
    this.onChange = fn
  }
  registerOnTouched(fn){
    this.onTouch = fn
  }

  propagateChange(_){

  }

  selectClicked(event: any) {
    const ele = event.srcElement.parentNode;
    ele.classList.toggle('cs-active');
  }

  selectedOption(ctrl: string, value: string) {
    this.onChange(value) // <-- CRUCIAL need to inform formControl to update the value 
    document.getElementById(ctrl).innerHTML = value;
    const ele = document.getElementById(ctrl).parentElement;
    ele.classList.toggle('cs-active');
  }

  closeDropDown(event: any) {
    const ele = event.srcElement;
    ele.classList.remove('cs-active');
  }
}

Now that we've added the ability to attach formControls to you custom component you can add them to the html in you app.component:

<form [formGroup]="parentForm">
    <app-common-dropdown placeHolder="select district" [dropDownId]="'districtLabel'" [dataList]="['bangalore','chennai','pune']" formControlName="district" ></app-common-dropdown>
    <app-common-dropdown placeHolder="select distance" [dropDownId]="'distanceLabel'" [dataList]="[100,200,300,400]" formControlName="distance" ></app-common-dropdown>
    <app-common-dropdown placeHolder="select state" [dropDownId]="'stateLabel'" [dataList]="['karnataka','tamil nadu','mumbai']" formControlName="state"  ></app-common-dropdown>
</form>

<button type="submit" (click)="getFormValues()">submit</button>

And you will need to adjust the names in you formGroup since they didnt match the html form

this.parentForm = this.fb.group({
  district: ['bangalore', Validators.required], <--- SETS THE DEFAULT VALUE OF THE FORM CONTROL
  distance: [''],
  state:['']
});

formControlName needs to match a property inside the parentForm.