CODEWITHSUNDEEP
typescriptangular
shmck
shmck

Reputation: 5609

Angular2 pass attribute to class constructor

How do I pass attributes from a parent component to their child components' class constructor in Angular 2?

Half of the mystery is figured out, as attributes can be passed to the view without problem.

/client/app.ts

import {Component, View, bootstrap} from 'angular2/angular2';
import {Example} from 'client/example';

@Component({
  selector: 'app'
})
@View({
  template: `<p>Hello</p>
    <example [test]="someAttr"
      [hyphenated-test]="someHyphenatedAttr"
      [alias-test]="someAlias"></example>
    `,
  directives: [Example]
})
class App {
  constructor() {
    this.someAttr = "attribute passsed to component";
    this.someHyphenatedAttr = "hyphenated attribute passed to component";
    this.someAlias = "attribute passed to component then aliased";
  }
}

bootstrap(App);

/client/example.ts

import {Component, View, Attribute} from 'angular2/angular2';

@Component({
  selector: 'example',
  properties: ['test', 'hyphenatedTest', 'alias: aliasTest']
})
@View({
  template: `
    <p>Test: {{test}}</p>
    <!-- result: attribute passsed to component -->
    <p>Hyphenated: {{hyphenatedTest}}</p>
    <!-- result: hyphenated attribute passed to component -->
    <p>Aliased: {{alias}}</p>
    <!-- result: attribute passed to component then aliased -->

    <button (click)="attributeCheck()">What is the value of 'this.test'?</button>
    <!-- result: attribute passed to component -->
  `
})
/*******************************************************************
* HERE IS THE PROBLEM. How to access the attribute inside the class? 
*******************************************************************/
export class Example {
  constructor(@Attribute('test') test:string) {
     console.log(this.test); // result: undefined
     console.log(test); // result: null
  }
  attributeCheck() {
    alert(this.test);
  }
}

To re-iterate:

How can I access an attribute inside the child component's class passed in from the parent component?

Repo

Upvotes: 7

Views: 11310

Answers (2)

Eric Martinez
Eric Martinez

Reputation: 31777

Updated to beta.1

You can use ngOnInit for this

@Component({
  selector: 'example',
  inputs: ['test', 'hyphenatedTest', 'alias: aliasTest'],
  template: `
    <p>Test: {{test}}</p>
    <!-- result: attribute passsed to component -->
    <p>Hyphenated: {{hyphenatedTest}}</p>
    <!-- result: hyphenated attribute passed to component -->
    <p>Aliased: {{alias}}</p>
    <!-- result: attribute passed to component then aliased -->

    <button (click)="attributeCheck()">What is the value of 'this.test'?</button>
    <!-- result: attribute passed to component -->
  `
})
export class Example {

  ngOnInit() {
    console.log(this.test);
    this.attributeCheck();
  }

  attributeCheck() {
    alert(this.test);
  }
}

Upvotes: 11

haz111
haz111

Reputation: 764

If you want to have access to properties values in child component you can:

import {Component, View, Attribute} from 'angular2/angular2';

@Component({
  selector: 'example',
  properties: ['test', 'hyphenatedTest', 'alias: aliasTest']
})
@View({
  template: `
    <p>Test: {{_test}}</p>
    <!-- result: attribute passsed to component -->
    <p>Hyphenated: {{_hyphenatedTest}}</p>
    <!-- result: hyphenated attribute passed to component -->
    <p>Aliased: {{_alias}}</p>
    <!-- result: attribute passed to component then aliased -->
  `
})
export class Example {
  _test: string;
  _hyphenatedTest: any; //change to proper type
  _alias: any; //change to proper type

  constructor() {
  }

  set test(test) {
    this._test = test;
  }

  set hyphenatedTest(hyphenatedTest) {
    this._hyphenatedTest = hyphenatedTest;
  }

 set alias(alias) {
    this._alias = alias;
  }

}

set method is run when the value of property changes. Value is passed to your local variable on which you can operate in component.

Important things:

  • set method is always executed after constructor
  • I don't know why but the name of parameter in set method must be same as name of this method (so it means it must be the same as name of property)

Upvotes: 0

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