The functionality of the Angular directive ngIf is not meeting the desired outcome

We are currently working on transferring data from one component to another using the approach outlined below. We want to display an error message when there is no data available.

<div *ngIf="showGlobalError">
      <h6>The reporting project doesn't have any Shippable Items</h6>
  </div>

The code in the component.ts file looks like this:

showGlobalError = true;
constructor(private psService: ProjectShipmentService, private pdComp: ProjectDetailsComponent) {
    this.psService.tDate.subscribe(x => this.cachedResults = x);
  }
  ngOnInit() {    }

  ngDoCheck() {
    if (this.cachedResults.length > 0 && this.count <= 1) {
        this.showGlobalError = false;
        this.populateArrays();
        this.count++;
      }
  }    
  populateArrays() {
    this.reportingProject = [this.pdComp.rProjectNumber];
    this.projectSalesOrder = this.pdComp.rSalesOrder;
    this.clearFilter();
  ........

We are facing an issue where even though there is data present in this.cachedResults (i.e., this.cachedResults.length is not equal to '0'), for a few seconds, the error message 'The reporting project doesn't have any Shippable Items' is shown on the page before displaying the actual data. We suspect that there may be an issue with the ngDoCheck() function causing this delay. Any assistance or insights would be greatly appreciated.

Answer №1

By default, the error message is displayed upon page load because the value of showGlobalError is set to true.

To resolve this, adjust the default setting to false and only display the error message when either this.cachedResults.length equals 0, or this.cachedResults is undefined, or this.cachedResults is null.

Hoping that these modifications address your issue effectively.

Answer №2

Instead of manually subscribing in your code, utilize the async pipe within your template

items$ = this.psService.tDate;

showGlobalError$ = this.items$.pipe(map(results => !results || !results.length));

constructor(private psService: ProjectShipmentService, private pdComp: ProjectDetailsComponent) { }

and within your template

<div *ngIf="showGlobalError$ | async">
  <h6>The reporting project doesn't have any Shippable Items</h6>
</div>

<ng-template *ngFor="let item of items$ | async">
  Do stuff with {{item | json}}
</ng-template>

This method handles your subscription automatically, resolving the memory leak issue caused by not unsubscribing from subscriptions.

Check out a library I developed for simplifying data caching in Angular applications: https://medium.com/@adrianbrand/angular-state-management-with-rxcache-468a865fc3fb

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