Transferring an array of interfaces between Angular 2 components

Encountering issues with passing an Array of data between components using @Input. Here is the code snippet:

public ngOnInit() {
    this.applications = new Array<ApplicationEntryInterface>();
(...)
let shortTermData = new ShortTermApplicationAdapter(application);
this.applications.push(shortTermData);
console.log(this.applications);
}

The console log displays a normal array https://i.sstatic.net/v4eEM.jpg in parent.component.html.

<student-application-overview [applicationsEntry]="applications"></student-application-overview>

Child component:

@Input('applicationsEntry') public applicationsEntry: Array<ApplicationEntryInterface>;
 ngOnChanges() {
console.log(this.applicationsEntry);
console.log(this.applicationsEntry.length); <--- shows 0
}

This results in https://i.sstatic.net/bW7Hx.jpg. It appears impossible to iterate through it using for loops, foreach loops, etc. Only *ngFor seems to work, as this.applicationsEntry.length remains at 0. How can I address this issue? I have also tried utilizing @Input (..) set (..) { (..) } with no success.

Answer №1

The issue lies within the ChangeDetection mechanism of Angular, specifically when updating the Array property in the parent component.

Simply appending new items to an Array does not trigger the child components to recognize changes in the OnChanges lifecycle hook.

To address this common problem, you can implement something similar on the parent component:

let updatedData = new UpdatedApplicationAdapter(application);
this.applications.push(updatedData);
this.applications = [...this.applications]; // This step is key

The last line effectively creates a new duplicate of the Array, prompting Angular's ChangeDetection system to acknowledge alterations made to Arrays.

Answer №2

Although I am new to Angular, I have found this syntax to be very useful when working with input:

@Input() applicationsEntry: Array<ApplicationEntryInterface>;

Answer №3

My approach involves using the ngOnChanges method along with the changes parameter. This method will only execute if the current value is different from the previous one, so creating a new object each time should work perfectly fine.

The changes variable keeps track of all the modified items within the component.

Here's an example:

ngOnChanges(changes: any) {
      if (changes.applicationsEntry) { // this prevents undefined values
         console.log(changes.applicationsEntry.currentValue); // your updated array will be displayed here
      }
  }

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