Angular Reactive forms

Angular Forms

Introduction

Angular provides two types of forms

• Template Driven
  • Easy to use
  • Familar to Angular JS
  • Two-way data binding-> minimal component code
  • Automatically tracks from and input element state
• Reactive (model driven
  • More flexible
  • Immutable data model
  • Easier to perform an action on value change
  • Access Reactive transformations such as DebounceTime or DistinctUntilChanged
  • Easily add input elements dynamically
  • Easier unit testing

Template driven forms put the responsibility in the template using basic HTML and data binding, Reactive forms move most of the responsibility to the component class

Template-Driven-Forms

In the Template we have

• Form elements
• Input elements
• Data binding to the component
• Validation rules (attributes)
• Validation error messages
• Form model (automatically generated)

In the Component Class we have

• Properties for data binding
• Method for form Operations such as submit

Directives used are

• ngForm
• ngModel
• ngModelGroup

Example form

<form (ngSubmit)="save()">
  <input id="firstNameId" type="text"
  [(ngMode)]="customer.firstname"
  name="firstname"
  #firstNameVar="ngModel" />
</form>

Reactive Forms

In the template we have

• Form elements
• Input elements
• Binding to form model

In the class we have

• Form model which we create
• Validation rules
• Validation error messages
• Properties for managing data (data model)
• Methods for form Operations such as submit

Directives used (ReactiveFormsModule)

• formGroup
• formControl
• formControlName
• formGroupName
• formArrayName

Template vs Reactive Example

Template form example

Reactive form example

Create a Reactive Form

Preparation

Make sure we import the ReactiveFormsModule in app.module.ts

Component Creation

Create a FormGroup in ngInit. Note we can initialize the controls at creation

export class CustomerComponent implements OnInit {
...  
  customerForm :FormGroup

  ngOnInit(): void {
    this.customerForm = new FormGroup({
      firstName: new FormControl(),
      lastName: new FormControl(),
      emailName: new FormControl(),
      sendCatog: new FormControl(true)
    })
  }
...

To set the values of the components you can use setValue or patchValue. Patch value will set a subset of the fields

export class CustomerComponent implements OnInit {
      customerForm.patchValue({
         firstName: 'Jack'
      }
  }
...

Now we can use FormBuilder using injection to simplify the code.

...
  constructor(private formBuilder: FormBuilder) {}

  ngOnInit(): void {

    this.customerForm = this.formBuilder.group({
       firstName: '',
       lastName: '',
       email: '',
       sendCatalog: true,
    })

Template Creation

We specify the form using the formGroup

  <div class="card-body">
    <form novalidate
          (ngSubmit)="save()"
          [formGroup]="customerForm">
...

We add fields with formControlName tag. Note getting this wrong, e.g. the name or the tag will result in the form not being rendered correctly. You can test this by adding a

MEEEEETemplate:FormName.dirty to find out where the error is.

          <input class="form-control"
                 id="emailId"
                 type="email"
                 placeholder="Email (required)"
                 required
                 email
                 formControlName='email'
                 [ngClass]="{'is-invalid': (customerForm.get('email').touched || customerForm.get('email').dirty) && !customerForm.get('email').valid }" />

Accessing Form Model Properties

In the template we can use

customerForm.controls.firstName.valid 
customerForm.get('firstName').valid

Or create a reference in the component to be used, in this case firstName

this.customerFrom = new FormGroup({
   firstName: this.firstName
})

Validation

Basic

We can set basic rules by passing an array of validators at creation time. Below we pass the default value and an array of validators e.g.

this.customerForm  this.formBuilder.group({
   firstName: ['default value'],
     [Validators.required, Validators.minLength(3)]],
   nextField: ''
...

At Runtime

We can do this with

  myEdit.setValidators(...);
  myEdit.clearValidators();
  myEdit.updateValueAndValidity()

Below is an example of handling a radio button on the form ===Component

  setNotification(notifyVia: string): void {
    const phoneControl = this.customerForm.get('phone');
    if (notifyVia === 'text') {
      phoneControl.setValidators(Validators.required);
    } else {
      phoneControl.clearValidators();
    }
    phoneControl.updateValueAndValidity();
  }

Template

      <div class="form-group row mb-2">
        <label class="col-md-2 col-form-label pt-0">Send Notifications</label>
        <div class="col-md-8">
          <div class="form-check form-check-inline">
            <label class="form-check-label">
              <input class="form-check-input"
                     type="radio"
                     value="email"
                     formControlName="notification"
                     (click)="setNotification('email')">Email
            </label>
          </div>
          <div class="form-check form-check-inline">
            <label class="form-check-label">
              <input class="form-check-input"
                     type="radio"
                     value="text"
                     formControlName="notification"
                     (click)="setNotification('text')">Text
            </label>
          </div>
        </div>
      </div>