How do I find the length of an associative array in ActionScript 3.0?

问题

Is there a simple way to retrieve the length of an associative array (implemented as an Object) in ActionScript 3.0?

I understand that there are two primary ways of creating associative arrays in AS3:

Use a Dictionary object; especially handy when the key does not need to be a string
Use an Object, and simply create properties for each desired element. The property name is the key, and the value is, well, the value.

My application uses approach #2 (using the Object class to represent associative arrays).

I am hoping there is something more native than my for loop, which manually counts up all the elements.

回答1:

You have to count them in a for loop as you do. Of course, you could make a class and stick the for loop in that class.

For some great implmentations of Collections in AS3, check these guys.

Edit 2013 Not surprisingly, links do break after time. Try this new one: http://www.grindheadgames.com/get-the-length-of-an-object.

回答2:

Doing a few tests on this has actually surprised me. Here's normal use of an Array:

var things:Array = [];
things.push("hi!");
trace(things.length);
// traces 1
trace(things);
// traces hi!

Here's if we set a value to a string:

var things:Array = [];
things["thing"] = "hi!";
trace(things.length);
// traces 0
trace(things);
// traces an empty string
trace(things["thing"]);
// traces hi!

Basically if you add things using strings you're setting properties rather than actually adding to the array. Makes me wonder why Array is dynamic in this way.

So... yeah count the items with a for ... in loop!

回答3:

I think you're stuck with counting them "manually".

An option would be to wrap the whole thing in a class and keep a separate variable that you update as you add/remove.

回答4:

var count:int; 
var key:String; 

for (key in myObject)
{ 
    count++; 
} 

trace ("myObject has this many keys in it: " + count);

or, alternatively, the for-each syntax (I haven't tested to see which is faster)

for each (var o:* in myObject)
{
    count++;
}

来源：https://stackoverflow.com/questions/284947/how-do-i-find-the-length-of-an-associative-array-in-actionscript-3-0

标签

apache-flex

actionscript-3

arrays