ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: ‘undefined’

you have to tell angular that you updated the content after ngAfterContentChecked
you can import ChangeDetectorRef from @angular/core and call detectChanges

import { ChangeDetectorRef } from '@angular/core';

constructor( private cdref: ChangeDetectorRef ) {}   

ngAfterContentChecked() {
    this.sampleViewModel.DataContext = this.DataContext;
    this.sampleViewModel.Position = this.Position;
    this.cdref.detectChanges();
 }