Advanced XML filtering

Question

Hi,
In short: How do I filter an XMLList in ActionScript rather
than E4X, i.e. I am looking for a
replacement of myXmlList.(@attrib == someValue) with
myXmlList.filter(someFilterFunction)
which has the same behaviour (i.e. the result does not
contain copies).
The long story: I have an application that operates on an XML
structure. It uses the E4X filter
mechanism to generate a number of filtered views to display,
using
filteredList:XMLList = myXmlList.(@attrib == someValue)
I now hit the situation that the filter functionality is more
complicated (I basically need access to the whole object and
perform a few calculations to decide whether it's in the list).
First quesiton: Is there an easy way to do this straight on the
XMLList?
I tried something like this
var filteredList:XMLListCollection = new
XMLListCollection(new XMLList());
for each (var n:XML in myXmlList) {
if (logic to decide whether n is in here) {
filteredList.addItem(n); (*** see below)
filteredList = XMLList(filteredList);
But this seems add each item again to myXmlList (so they are
all in there twice now) - no what I want.
Second question: What exactly is the addItem call doing? Why
is it also adding to the XMLList n is from?
I tried
filteredList.addItem(n.copy());
which does not add the items to myXmlList but it makes a copy
which is not what I want (I am updating the
XML and don't want to have copies around). This whole
approach may be complete nosense, I am just
starting to get my head around the XML processing.
Any help or pointers in the right direction are much
appreciated.
Thanks,
Robert

Answer 1

You are so close. You are saying the right words but not
conjuring the right spell. You do want a filtering function - you
want a filterFunction:
var bigList:XMLListCollection = new XMLListCollection(
originaldata );
bigList.filterFunction = uniqueFilter;
private function uniqueFilter( item:Object ) : Boolean {
var test:XML = XML(item);
if( /* some test here */ ) return true; else return false;
bigList.refresh();
If you look at the documentation for XMLListCollection and
then examine the inherited properties and methods, you'll see the
filterFunction property and the refresh method.
I just wrote an article on my blog about filtering
collections. Although I used ArrayCollection, it should similarly
for XMLListCollection.
Filtering
Collections - weblogs.macromedia.com/pent
Basically the filterFunction is given an element of the
Collection and must return true if the element should appear in the
collection's view or false if should not. This does not eliminate
the item from the Collection, just from the view of the Collection.
This way you can change the criteria and refresh() the collection.
If you have a DataGrid's dataProvider bound to the Collection
you'll see it just when the refresh() is done.