Is the calling of Angular template functions triggered each time the user interface is updated?

I created this demonstration and I want to verify my understanding of the dynamics involved.

In this demo, whenever a checkbox is selected, it triggers a merge of observable checkbox events.

This trigger leads to the update of an array containing instances that determine whether columns in a material table should be hidden or displayed.

The component also includes a method that defines the columns for the material table:


  getDisplayedColumns(): string[] {
    return this.columnDefinitions.filter(cd => !cd.hide).map(cd => cd.def);
  }

If I understand correctly, this method is called each time the user interface is updated. In other words, Angular Change Detection triggers its execution?

javascriptangulartypescriptrxjsangular-material

Answer №1

Each time the template goes through a change detection cycle, your method is triggered. The change detection process scans for any modifications in the component's model and updates the corresponding parts.

However, you have control over how the change detection process operates by defining the change detection strategy for your component.

Modes of Change Detection

By default, change detection is initiated by various events like clicks, scrolls, or asynchronous actions, potentially resulting in the method being called multiple times.

Alternatively, you can specify 

changeDetection: ChangeDetectionStrategy.OnPush
in your component to trigger change detection only when there are changes in the @Input() properties.

But this solution addresses only part of the issue...

Avoiding Method Calls in Templates

The other part involves refraining from using methods directly in the template and instead utilizing class properties. This principle applies to getters as well.

<mat-row *matRowDef="let row; columns: columns"></mat-row>

All you need to do is update this.columns within your class when it truly needs to be modified.

I trust this information proves beneficial.

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