How to fix closure problem in ActionScript 3 (AS3)

Question

In the code below I\'m trying to load some images and put them in the stage as soon as they get individually loaded. But it is bugged since only the last image is displayed.

Answer 1

Using the more functional style forEach method on the Array class avoids this problem. This has been mentioned already but I'll expand on it here.

imageList.forEach( function ( item:MovieClip, index:int, list:Array) {
    // add your listener with closure here
})

Using this method, the function passed into the forEach defines a new scope each iteration. now you can add a closure inside this scope and it will remember each instance as you want.

On a related note:

Typing those 3 arguments the whole time is a pain so... You can also make that less / more ugly with an adaptor function:

// just give me the item please
imageList.forEach ( itrAdpt( function ( image: ImageData ) {
    // add your listener with closure here
}))

// give me the item and it's index
imageList.forEach ( itrAdpt( function ( image: ImageData, index:int ) {
    // add your listener with closure here
}))

// give me the item, index and total list length
imageList.forEach ( itrAdpt( function ( image: ImageData, index:int, length:int ) {
    // add your listener with closure here
}))

where itrAdpt is a (possibly global) function defined something like:

public function itrAdpt(f: Function): Function
{
    var argAmount:int = f.length

    if (argAmount == 0)
    {
        return function (element:*, index:int, colection:*):* {
            return f(element)
        }
    }
    else if (argAmount == 1)
    {
        return function (element:*, index:int, colection:*):* {
            return f(element)
        }
    }
    else if (argAmount == 2)
    {
        return function (element:*, index:int, colection:*):* {
            return f(element, index)
        }
    }
    else if (argAmount == 3)
    {
        return function (element:*, index:int, colection:*):* {
            return f(element, index, colection.length)
        }
    }
    else
    {
        throw new Error("Don't know what to do with "+argAmount+"arguments. Supplied function should have between 1-3 arguments")
    }
}