Barefoot Development

Custom Class Casting in Flash

While developing a Flash 8 project using ActionScript 2 classes, I recently created a Tile class that extended MovieClip. The Tile is a custom scrolling background element that tiles itself for a seamless, endless horizontal scrolling.

I created a couple variables, typed as Tile, in my AppState class, the class I use to keep the current state of the Flash application. They are like so:

// Background movie clip tile references
var tile1:Tile = null;
var tile2:Tile = null;

Now, since we're not yet using ActionScript 3, the only way to place new Tile instances onto the stage is with a call to attachMovie(). However, the following call won't compile in AS2:

app.tile1 = _root.attachMovie(bgndMcName, "bgnd1_mc", app.depth++);

Why does it fail? Well, the compiler says this:

Type mismatch in assignment statement: found MovieClip where is required.

So, I thought to myself, I wonder if you can cast objects like you can with the String() and Number() functions? It turns out you can! This works:

app.tile1 = Tile(_root.attachMovie(bgndMcName, "bgnd1_mc", app.depth++));

I'm looking forward to ActionScript 3, where we will be able to instantiate objects to be placed on the stage like you can for any other object:

app.tile1 = new Tile();

But until then, I'll use this casting method. It's not rocket science, but I thought it was cool nonetheless.

Doug Smith, Senior Developer, Barefoot


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