ngOnInit and constructor who run first

Question

When I call my service injected in the constructor, I get undefined. the service is called in ngOnInit method, From Difference between Constructor and ngOnInit I have seen that constructor run first , but in my case I noted the opposite, so I'm bit confused. have someone more explication about that, thanks.

constructor(private curveService  :ProgressCurveService, private util : UtilService) {
    this.startPickerOptions = new DatePickerOptions();
    this.endPickerOptions = new DatePickerOptions();
    //this.datePickerOptions.initialDate = new Date(Date.now());
   }

ngOnInit() {
    this.curveService.instance.getCurve(this.startDate.formatted,this.endDate.formatted,this.amplutid).
    then(res => {

        this.lineChartLabels = this.util.dateToShortString(Object.keys(res.progressPlotData))
        this.lineChartData = this.util.objectToIntArray(res.progressPlotData);
    }).catch(res => console.log('error if date selecting ...'));
}

progress curve service:

import { progressCurveItf } from './progress-curve/progress-curve-interface';

@Injectable()
export class ProgressCurveService {

    state : string = 'project';
  constructor(private prsCurve : PrsProgressCurveService, private projCurve : ProjProgressCurveService) { }
  get instance():progressCurveItf{

    if(this.state == 'subproject'){
        return this.prsCurve;
    } else {
        return this.projCurve;
    }
  } 

}

The constructor runs first. The problem has to come from somewhere else. — Günter Zöchbauer, Mar 15 '17 at 09:18
exactly , already explained in documentation too that constructor runs first — Pardeep Jain, Mar 15 '17 at 09:19
can you add ProgressCurveService to the question? also where did you set this as provider? — Suraj Rao, Mar 15 '17 at 09:25
ProgressCurveService Provided by ngmodule and when I use it in click method it work — mustafa918, Mar 15 '17 at 09:33

score 0 · Accepted Answer · answered Mar 15 '17 at 10:39

0

While you're returning an instance of type progressCurveItf that is an interface I think there is something wrong with the instantiation of what you're returning, check if you provide PrsProgressCurveService and ProjProgressCurveService.

answered Mar 15 '17 at 10:39

mustafa918

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score 0 · Answer 2 · answered Sep 03 '19 at 07:10

To answer your question Constructor will get invoked since it belongs to ES6, basically which got the first priority. Where as ngOnInit is a life cycle hook designed by angular team which will get invoked after constructor even after ngOnChanges life cycle hook.

Constructor -> ngOnChanges -> ngOnInit -> followed by other life cycle hooks

ngOnInit and constructor who run first

2 Answers2