typescript - Expression ___ has changed after it was checked

Question

Why is the component in this simple plunk

@Component({
  selector: 'my-app',
  template: `<div>I'm {{message}} </div>`,
})
export class App {
  message:string = 'loading :(';

  ngAfterViewInit() {
    this.updateMessage();
  }

  updateMessage(){
    this.message = 'all done loading :)'
  }
}

throwing:

EXCEPTION: Expression 'I'm {{message}} in App@0:5' has changed after it was checked. Previous value: 'I'm loading :( '. Current value: 'I'm all done loading :) ' in [I'm {{message}} in App@0:5]

when all I'm doing is updating a simple binding when my view is initiated?

Answer 1

As stated by drewmoore, the proper solution in this case is to manually trigger change detection for the current component. This is done using the detectChanges() method of the ChangeDetectorRef object (imported from angular2/core), or its markForCheck() method, which also makes any parent components update. Relevant example:

import { Component, ChangeDetectorRef, AfterViewInit } from 'angular2/core'

@Component({
  selector: 'my-app',
  template: `<div>I'm {{message}} </div>`,
})
export class App implements AfterViewInit {
  message: string = 'loading :(';

  constructor(private cdr: ChangeDetectorRef) {}

  ngAfterViewInit() {
    this.message = 'all done loading :)'
    this.cdr.detectChanges();
  }

}

Here are also Plunkers demonstrating the ngOnInit, setTimeout, and enableProdMode approaches just in case.