A guide on transferring received data from dataService within the parent component to the child component in Angular2

Within the context of my application, there exists a parent component named app-parent and a child component called app-child. In app-parent, I retrieve data from a DataService.

@Component({
  selector: 'app-parent',
  providers: [DataService]
})

export class Part1Component implements OnInit {
  public title: string;

  constructor(public dataService: DataService) {}

  ngOnInit() {
    this.dataService.get().subscribe(data => {
      this.itemsSource = this.dataService.convert(data, 1);
      this.title = this.itemsSource[0];
          });
   return this.title;
  }

The template is as follows:

 <div id="content">Hello!</div>
    <app-child [title]='title'></app-child>

I want to pass the title to the child component. The code in my child component looks like this:

@Injectable()
  export class InfoComponent implements OnInit, OnDestroy {
  @Input() title: any;

  ngOnInit() {
    console.log('Displaying title')
    console.log(this.title);
}

While attempting to use @Input() to pass the data, it doesn't work as expected (I receive undefined instead of the title). This issue arises because in the parent component, the data from DataService is obtained first (setting the title explicitly at the start, e.g., in app-parent, works successfully).

Can you please provide guidance on resolving this problem?

Answer №1

When the child component's OnInit is fired, the data is fetched asynchronously and the title may not yet have a value. By using OnChanges, you can monitor changes in the @Input. Here's an example of how you can utilize it:

ngOnChanges() {
  console.log('Show me title')
  console.log(this.title);
}

This code snippet will execute every time there is a change in the Input title. To ensure you are working with a valid title before performing any operations on it, consider adding a conditional check to verify its existence. Initially, during the first execution(s) of ngOnChanges, the title will be undefined.

Additionally, it seems that your attempt to use return title in the parent component won't return any meaningful value retrieved from within the subscribe block. Furthermore, I noticed that your child component is labeled as an Injectable, which does not seem relevant to the issue at hand but deserves mentioning.

Answer №2

As you navigate to the child page

 import { NavController,........} from 'ionic-angular';
 .
 .
 this.dataService.fetch().subscribe(response => {
  this.items = this.dataService.transform(response, 2);
  this.itemTitle = this.items[0];
  this.navCtrl.push(ChildPage, { item: this.itemTitle })
 });
 .
 .

Once you are on the child page

 import { NavParams,............} from 'ionic-angular';
 .
 .
 this.itemTitle = navParams.get('item')
 .
 .

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