observable - Merge ObservableCollections and being notified of changes? -

i want merge x collections , being notified if 1 of changed (add/remove).

i have following code using compositecollection i'm not notified when changes in sub-collections.

void main() {     var col1 = new observablecollection<string>();     var col2 = new observablecollection<string>();     var col3 = new observablecollection<string>();      col1.add("item 1-1");     col1.add("item 1-2");     col2.add("item 2-1");      var cc = new compositecollection();     cc.add(col1);     cc.add(col2);      var ncc = (inotifycollectionchanged)cc;     ncc.collectionchanged += collectionchanged;      //col3.add("item 3-1");     //cc.add(new collectioncontainer() { collection = col3 });      col1.add("item 1-3");     col2.add("item 2-2"); }  public void collectionchanged(object sender, notifycollectionchangedeventargs e) {     "collection changed!".dump(); } 

i'm notified if collection added compositecollection (the 2 commented lines) not if add col1 or col2...

is there way achieve easily? (i have solution using observables seems using cannon kill fly...)

thanks help!