TypeError: Cannot read property 'get' of undefined Ionic 3 /Angular 5

Question

I got the below error on Ionic 3 app.

TypeError: Cannot read property 'get' of undefined
    at Object.eval [as updateDirectives] (ng:///NewLoginPageModule/NewLoginPage.ngfactory.js:196:39)
    at Object.debugUpdateDirectives [as updateDirectives] (http://localhost:8100/build/vendor.js:14693:21)
    at checkAndUpdateView (http://localhost:8100/build/vendor.js:13862:14)
    at callViewAction (http://localhost:8100/build/vendor.js:14212:21)
    at execComponentViewsAction (http://localhost:8100/build/vendor.js:14144:13)
    at checkAndUpdateView (http://localhost:8100/build/vendor.js:13868:5)
    at callViewAction (http://localhost:8100/build/vendor.js:14212:21)
    at execEmbeddedViewsAction (http://localhost:8100/build/vendor.js:14170:17)
    at checkAndUpdateView (http://localhost:8100/build/vendor.js:13863:5)
    at callViewAction (http://localhost:8100/build/vendor.js:14212:21)

.ts

    ulLoginForm: FormGroup;

    constructor(private formBuilder: FormBuilder) {}

     ionViewDidLoad() {
       this.initForm();
     }

  initForm() {
    this.ulLoginForm = this.formBuilder.group({
       password: ['', Validators.required]
    })
  }

.html

 <form [formGroup]="ulLoginForm">                           
        <ion-list>
         <ion-item>
        <ion-input type="password" placeholder="Password"  formControlName="password"></ion-input>
        <p *ngIf="ulLoginForm.get('password').hasError('required') && ulLoginForm.get('password').touched" class="error" padding-left>Password
        is empty</p>
         </ion-item>
        </ion-list>
    </form>

Answer 1

the problem is that you want to access the formControl, but the initialization of the form is after the initialization of the component (because the ionViewDidLoad is executed after).

you could try to call the initForm() in the ngOnInit method, this is a lifecycle method of the angular framework:

export class YourComponent implements OnInit{    
    ulLoginForm: FormGroup;

    constructor(private formBuilder: FormBuilder) {}

    ngOnInit() {
       this.initForm();
     }
}