Angular Dynamic form observable property binding - forms

Question

I have a problem with some dynamically generated forms and passing values to them. I feel like someone must have solved this, or I’m missing something obvious, but I can't find any mention of it.
So for example, I have three components, a parent, a child, and then a child of that child. For names, I’ll go with, formComponent, questionComponent, textBoxComponent. Both of the children are using changeDetection.OnPush.
So form component passes some values down to questionComponent through the inputs, and some are using the async pipe to subscribe to their respective values in the store.
QuestionComponent dynamically creates different components, then places them on the page if they match (so many types of components, but each questionComponent only handles on one component.
some code:
#Input() normalValue
#Input() asyncPipedValue
#ViewChild('questionRef', {read: ViewContainerRef}) public questionRef: any;
private textBoxComponent: ComponentFactory<TextBoxComponent>;
ngOnInit() {
let component =
this.questionRef.createComponent(this.checkboxComponent);
component.instance.normalValue = this.normalValue;
component.instance. asyncPipedValue = this. asyncPipedValue;
}
This works fine for all instances of normalValues, but not for asyncValues. I can confirm in questionComponent’s ngOnChanges that the value is being updated, but that value is not passed to textBoxComponent.
What I basically need is the async pipe, but not for templates. I’ve tried multiple solutions to different ways to pass asyncValues, I’ve tried detecting when asyncPipeValue changes, and triggering changeDetectionRef.markForChanges() on the textBoxComponent, but that only works when I change the changeDetectionStrategy to normal, which kinda defeats the performance gains I get from using ngrx.
This seems like too big of an oversight to not already have a solution, so I’m assuming it’s just me not thinking of something. Any thoughts?

Answer 1

I do something similar, whereby I have forms populated from data coming from my Ngrx Store. My forms aren't dynamic so I'm not 100% sure if this will also work for you.
Define your input with just a setter, then call patchValue(), or setValue() on your form/ form control. Your root component stays the same, passing the data into your next component with the async pipe.
#Input() set asyncPipedValue(data) {
if (data) {
this.textBoxComponent.patchValue(data);
}
}
patchValue() is on the AbstractControl class. If you don't have access to that from your question component, your TextBoxComponent could expose a similar method, that can be called from your QuestionComponent, with the implementation performing the update of the control.
One thing to watch out for though, if you're also subscribing to valueChanges on your form/control, you may want to set the second parameter so the valueChanges event doesn't fire immediately.
this.textBoxComponent.patchValue(data, { emitEvent: false });
or
this.textBoxComponent.setValue(...same as above);
Then in your TextBoxComponent
this.myTextBox.valueChanges
.debounceTime(a couple of seconds maybe)
.distinctUntilChanged()
.map(changes => {
this.store.dispatch(changes);
})
.subscribe();
This approach is working pretty well, and removes the need to have save/update buttons everywhere.

Answer 2

I believe I have figured out a solution (with some help from the gitter.com/angular channel).
Since the values are coming in to the questionComponent can change, and trigger it's ngOnChanges to fire, whenever there is an event in ngOnChanges, it needs to parse through the event, and bind and changes to the dynamic child component.
ngOnChanges(event) {
if (this.component) {
_.forEach(event, (value, key) => {
if (value && value.currentValue) {
this.component.instance[key] = value.currentValue;
}
});
}
}
This is all in questionComponent, it resets the components instance variables if they have changed. The biggest problem with this so far, is that the child's ngOnChanges doesn't fire, so this isn't a full solution. I'll continue to dig into it.

Answer 3

Here are my thoughts on the question, taking into account limited code snippet.
First, provided example doesn't seem to have anything to do with ngrx. In this case, it is expected that ngOnInit runs only once and at that time this.asyncPipedValue value is undefined. Consequently, if changeDetection of this.checkboxComponent is ChangeDetection.OnPush the value won't get updated. I recommend reading one excellent article about change detection and passing async inputs. That article also contains other not less great resources on change detection. In addition, it seems that the same inputs are passed twice through the component tree which is not a good solution from my point of view.
Second, another approach would be to use ngrx and then you don't need to pass any async inputs at all. Especially, this way is good if two components do not have the parent-child relationship in the component tree. In this case, one component dispatches action to put data to Store and another component subscribes to that data from Store.
export class DataDispatcherCmp {
constructor(private store: Store<ApplicationState>) {
}
onNewData(data: SomeData) {
this.store.dispatch(new SetNewDataAction(data));
}
}
export class DataConsumerCmp implements OnInit {
newData$: Observable<SomeData>;
constructor(private store: Store<ApplicationState>) {
}
ngOnInit() {
this.newData$ = this.store.select('someData');
}
}
Hope this helps or gives some clues at least.