Looking through all the existing valueAccessors examples in the AngularJS
source code doesn't help because all of them simply update existing DOM
elements. As such, the writeValue() method never updates anything that is
part of dirty-checking.
I need to update the value of an AngularJS component, based on the
writeValue().
On Sunday, January 31, 2016 at 6:54:54 AM UTC-5, Ben Nadel wrote:
>
> I am trying to understand how to create custom valueAccessor
> implementations to bind [ngModel] to an existing Widget directive in order
> to give it two-way data binding. So, imagine that I have:
>
> Widget
> inputs: [ "value" ] ---> Sets the selected value of the widget.
> outputs: [ "select" ] ---> Emits event when value *should be selected*
> (ie, doesn't change it internally).
>
> Ok, now I'm trying to create a valueAccessor that selects on
> "widget[ngModel]"... such that
>
> <widget [(ngModel)]="someValue" />
>
> ... will match TWO directives - the "Widget component" (which knows
> nothing about ngModel) and the "accessor directive."
>
> So far so good. Until I implement the *writeValue()* method:
>
> function writeValue( newValue ) {
> widget.value = newValue;
> }
>
> Here, Angular is throwing the error:
>
> Expression 'value in AppController@4:8' has changed after it was checked.
> Previous value: 'false'. Current value: 'true' in [value in
> AppController@4:8]
>
> If I wrap the "widget.value = newValue;" in a setTimeout(), the error goes
> away. But, I don't believe this is a *fix*. I think I am just missing
> something fundamental about change detection. Or valueAccessors.
>
> It almost as if the fact that both directives match on the same Node, one
> directive cannot alter the other's inputs. But, as they are different
> directives,
>
> Thanks!
>
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