angularruntime-error

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

I know there are a lot of same questions already posted in stack-overflow and tried different solutions to avoid the run-time error but None of them are working for me.

Error

Component and Html Code

export class TestComponent implements OnInit, AfterContentChecked {
    @Input() DataContext: any;
    @Input() Position: any;
    sampleViewModel: ISampleViewModel = { DataContext: : null, Position: null };
    constructor(private validationService: IValidationService, private modalService: NgbModal, private cdRef: ChangeDetectorRef) {
    }

    ngOnInit() {

    }
    ngAfterContentChecked() {

            debugger;
            this.sampleViewModel.DataContext = this.DataContext;
            this.sampleViewModel.Position = this.Position;

    }


<div class="container-fluid sample-wrapper text-center" [ngClass]="sampleViewModel.DataContext?.Style?.CustomCssClass +' samplewidget-'+ sampleViewModel.Position?.Columns + 'x' + sampleViewModel.Position?.Rows">
     //some other html here
</div>

Please Note : This Component is loaded dynamically using DynamicComponentLoader

After My trouble shooting I have identified couple of issues

First of all this child component is loaded dynamically by using DynamicComponentResolver and passing the input values like below

 ngAfterViewInit() {
    this.renderWidgetInsideWidgetContainer();

  }


  renderWidgetInsideWidgetContainer() {
    let component = this.storeFactory.getWidgetComponent(this.dataSource.ComponentName);
    let componentFactory = this._componentFactoryResolver.resolveComponentFactory(component);
    let viewContainerRef = this.widgetHost.viewContainerRef;
    viewContainerRef.clear();
    let componentRef = viewContainerRef.createComponent(componentFactory);
    debugger;
    (<IDataBind>componentRef.instance).WidgetDataContext = this.dataSource.DataContext;
    (<IDataBind>componentRef.instance).WidgetPosition = this.dataSource.Position;

  }

Even If I changed my child component html like below I am getting this same error.Just add a angular ngclass attribute

<div class="container-fluid ds-iconwidget-wrapper text-center" [ngClass]="Sample">

</div>

My databinding and everything are working fine.Do I need to do anything on parent component? I already tried all the lifecyle events in child component

Solution

  • The ngAfterContentChecked lifecycle hook is triggered when bindings updates for the child components/directives have already been finished. But you're updating the property that is used as a binding input for the ngClass directive. That is the problem. When Angular runs validation stage it detects that there's a pending update to the properties and throws the error.

    To understand the error better, read these two articles:

    Think about why you need to change the property in the ngAfterViewInit lifecycle hook. Any other lifecycle that is triggered before ngAfterViewInit/Checked will work, for example ngOnInit, ngDoCheck or ngAfterContentChecked.

    So in order to fix it, move renderWidgetInsideWidgetContainer to the ngOnInit() lifecycle hook.