PropertyChangeHandler, listening recursively for events from one Child versus All Children.

[pnakaska]

Given a parent class A that has a List of children of type class B

class A {

     private List <B> children;

}

class B {

     private String test;

}

the A class is Bound in an Errai Widget (AWidget.java):

  @Inject  @AutoBound  private DataBinder<A> aBinder;

and it's nested list of B instances is Bound using a ListWidget:

@Inject @Bound(property = "children")  @DataField  private ListWidget<B, BWidget> bList;

In the A class' Widget, using a PropertyChangeHandler, to listen for events from the nested list,

the "**" notation allows the parent (AWidget) to recursively hear events from any of the children:

aModelBinder.addPropertyChangeHandler("**", handler);

If any one of the (Bound) children change, the handler does receive events, but the source that arrives in the event

is the entire list, not the specific child that has changed.

Is there any way to specify that the source received in the event is the specific child that has changed? So that the whole

list need not be traversed to determine what's changed?

[csa]

Hi,

Yes, that's the way it should be, in my opinion. Your parent class / parent binder should get notified for the properties they have (nested) bindings for. The changed property in that case is "children". You can already find out what child in that list specifically changed by registering an change handler on the nested binder in BWidget.

Cheers,

Christian

[csa]

A possible solution to make your use-case more convenient would be to add a "cause" to the PropertyChangeEvent, which basically is a nested PropertyChangeEvent (i.e. for the child that changed). That would be clean as the parent would still receive the event for the property it has bindings for but could also dig deeper to find out more details (the cause of the change). The question is: Is this worth it?