Angular 2: How to detect changes in an array? (@input property)

You can always create a new reference to the array by merging it with an empty array:

this.yourArray = [{...}, {...}, {...}];
this.yourArray[0].yourModifiedField = "whatever";

this.yourArray = [].concat(this.yourArray);

The code above will change the array reference and it will trigger the OnChanges mechanism in children components.

You can use IterableDiffers

It's used by *ngFor

constructor(private _differs: IterableDiffers) {}

ngOnChanges(changes: SimpleChanges): void {
  if (!this._differ && value) {
     this._differ = this._differs.find(value).create(this.ngForTrackBy);
  }
}

ngDoCheck(): void {
  if (this._differ) {
    const changes = this._differ.diff(this.ngForOf);
    if (changes) this._applyChanges(changes);
  }
}

Read following article, don't miss mutable vs immutable objects.

Key issue is that you mutate array elements, while array reference stays the same. And Angular2 change detection checks only array reference to detect changes. After you understand concept of immutable objects you would understand why you have an issue and how to solve it.

I use redux store in one of my projects to avoid this kind of issues.

https://blog.thoughtram.io/angular/2016/02/22/angular-2-change-detection-explained.html

OnChanges Lifecycle Hook will trigger only when input property's instance changes.

If you want to check whether an element inside the input array has been added, moved or removed, you can use IterableDiffers inside the DoCheck Lifecycle Hook as follows:

constructor(private iterableDiffers: IterableDiffers) {
    this.iterableDiffer = iterableDiffers.find([]).create(null);
}

ngDoCheck() {
    let changes = this.iterableDiffer.diff(this.inputArray);
    if (changes) {
        console.log('Changes detected!');
    }
}

If you need to detect changes in objects inside an array, you will need to iterate through all elements, and apply KeyValueDiffers for each element. (You can do this in parallel with previous check).

Visit this post for more information: Detect changes in objects inside array in Angular2