Cannot access Inputs from my controller/constructor

I have a simple Angular 2 component with @Input, which I bind to the template. The template shows input data, but I cannot access it from the constructor:

import {Component, View, bootstrap, Input} from 'angular2/angular2';
import DataService from './data-service';

@Component({
    selector: 'app-cmp'
})
@View({
    template: `{{data.firstName}} {{data.lastName}}` //-> shows the correct 'data'
})
export default class NamesComponent {
  @Input() data: any;
  constructor(dataService: DataService) {
    console.log(this.data);//undefined
  }
}

Here is a plunker with an example (see "names-component.ts").

What am I doing wrong?

Solution 1:

Because the Input property isn't initialized until view is set up. According to the docs, you can access your data in ngOnInit method.

import {Component, bootstrap, Input, OnInit} from '@angular/core';
import DataService from './data-service';

@Component({
    selector: 'app-cmp',
    template: `{{data.firstName}} {{data.lastName}} {{name}}`
})
export default class NamesComponent implements OnInit {
  @Input() data;
  name: string;
  constructor(dataService: DataService) {
    this.name = dataService.concatNames("a", "b");
    console.log(this.data); // undefined here
  }
  ngOnInit() {
    console.log(this.data); // object here
  }
}

Solution 2:

You must implement OnChanges, see below:

import {Component, bootstrap, Input, OnChanges} from '@angular/core';
import DataService from './data-service';

@Component({
    selector: 'app-cmp',
    template: `{{data.firstName}} {{data.lastName}} {{name}}`
})
export default class NamesComponent implements OnChanges {
  @Input() data;
  name: string;
  constructor(dataService: DataService) {
    this.name = dataService.concatNames("a", "b");
    console.log(this.data); // undefined here
  }
  ngOnChanges() {
    console.log(this.data); // object here
  }
}