Flex / ActionScript: Copy an ArrayCollection

While working with an ArrayCollection I ran into a issue. It seems when you set one ArrayCollection equal to another they share memory space. This can cause issues when you perform any operation that will alter the internal array.

var arrayCollection1:ArrayCollection = new ArrayCollection([1,2,3,4,5]);
var arrayCollection2:ArrayCollection = arrayCollection1;

trace("arrayCollction1: " + arrayCollection1.toString());
trace("arrayCollction2: " + arrayCollection2.toString());

arrayCollection1.removeItemAt(0);

trace("arrayCollction1: " + arrayCollection1.toString());
trace("arrayCollction2: " + arrayCollection2.toString());

Output:
arrayCollection1: 1,2,3,4,5
arrayCollection2: 1,2,3,4,5

arrayCollection1: 2,3,4,5
arrayCollection2: 2,3,4,5

The simple solution for this is to always create a new ArrayCollection for the target using the toArray method from the source.

var arrayCollection1:ArrayCollection = new ArrayCollection([1,2,3,4,5]);
var arrayCollection2:ArrayCollection = new ArrayCollection(arrayCollection1.toArray());

trace("arrayCollection1: " + arrayCollection1.toString());
trace("arrayCollection2: " + arrayCollection2.toString());

arrayCollection1.removeItemAt(0);

trace("arrayCollection1: " + arrayCollection1.toString());
trace("arrayCollection2: " + arrayCollection2.toString());

Output: 
arrayCollection1: 1,2,3,4,5
arrayCollection2: 1,2,3,4,5

arrayCollection1: 2,3,4,5
arrayCollection2: 1,2,3,4,5

Those post is based on findings from this blog post.

Flex: Event Listeners and Array Collections

While working with some code I ran into a situation where I needed to know when an ArrayCollection was updated. Normally an event is triggered when using addItem, but I needed to know when it was set to another ArrayCollection. It's not very obvious, but it is possible.

ArrayCollection is really a wrapper for an Array. You can access the "real" array in an ArrayCollection by using ".source". When you set the source property an event called "listChanged" is triggered. You can watch for this event and then do whatever you need.

So this

var newAC1:ArrayCollection = new ArrayCollection;
var newAC2:ArrayCollection = new ArrayCollection;
newAC1 = newAC2;

Is the same as this, but with an event trigger.

var newAC1:ArrayCollection = new ArrayCollection;
var newAC2:ArrayCollection = new ArrayCollection;

newAC1.addEventListener('listChanged', function(event:Event){trace('changed');});

newAC1.source = newAC2.source;

Flex and dataProviders

Most seasoned Flex coders probably know this, but as always I'm still learning. When creating a dataProvider for a List or TileList it's best to use a ArrayCollection instead of an Array.

Arrays will work if you set them as a dataProvider, but sometimes they can act weird. I just spent the last hour trying to get a TileList to update that had a Array dataProvider. Once I changed it to an ArrayCollection it worked without a problem.

So learn from my mistake. Don't use Arrays for dataProviders.