Document static method approach

Kevin C. Coram 2020-01-08 22:05:39 -05:00
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# Parent Component Creates Form; Child Components Define Structure
Another approach for refactoring a component into child sub-components where the parent component is responsible for creating the entre Reactive Form would be to define static factory methods within each child component rather than within a full-fledged service. As with the [Parent Component Creates Form and Passes Form Controls Into Child Components (Global Form)](../global-form/ approach, the appropriate form controls would be passed into the children.
In many ways, this approach is a hybrid between the Parent Form and Global Form approaches.
export class AppComponent implements OnInit, OnDestroy {
contact: Contact;
form: FormGroup;
private subscription: Subscription;
constructor(private service: ContactService, private fb: FormBuilder) {}
public ngOnInit() {
this.subscription = this.service
.subscribe((data: Contact) => { = data;
this.form ={
name: NameComponent.buildForm(,
addresses: AddressListComponent.buildForm(data.addresses),
The HTML templating will be identical to the Global Form approach.
## Static Form Builder Methods
Rather than having a separate factory service, this approach uses static methods on each of the child sub-classes. This approach intentionally couples the logic for creating a sub-form structure with the component that would display it, keeping the logic in one place rather than separating it between components and an otherwise unrelated service. The rule-of-thumb in this approach is that the component which needs to display the form to a user will best know what the structure of that form needs to be.
### Name Component
static buildForm(name: Name): FormGroup {
return new FormGroup({
firstName: new FormControl(name ? name.firstName : ''),
lastName: new FormControl(name ? name.lastName : ''),
middleName: new FormControl(name ? name.middleName : ''),
prefix: new FormControl(name ? name.prefix : ''),
suffix: new FormControl(name ? name.suffix : ''),
### Address List Component
static buildForm(addresses: Address[]): FormArray {
const list: FormArray = new FormArray([]);
if (addresses) {
addresses.forEach(addr => {
return list;
### Address Component
static buildForm(addr: Address): FormGroup {
return new FormGroup({
line1: new FormControl(addr ? addr.line1 : ''),
line2: new FormControl(addr ? addr.line2 : ''),
city: new FormControl(addr ? : ''),
state: new FormControl(addr ? addr.state : ''),
postalCode: new FormControl(addr ? addr.postalCode : ''),
## Pros
- The child components encapsulate the form controls and their display, while keeping the form creation logic separate from the actual template rendering
- The child components can easily be re-used
## Cons
- The overall shape of the form from the parent component's perspective is not always clear