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Wait to fully-init instances in AS3?


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#1 IronyGames   Members   -  Reputation: 134

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Posted 09 August 2012 - 07:58 AM

Hi, I've recently been trying my hand at Actionscript game programming. Especifically, I want to build random mazes and check whether they have a path from start to end. These mazes, I store them in their Maze class/instances.

Of course, this takes time. Not a lot, but it's not immediate either. Looks like Flash won't wait for the maze to be checked though, and continues with other instructions related to using the information from the Maze, which seems to give me a "Error #1009: Can't refer to a null object yadda yadda".

Am I right in my suspicions? If so, what can I do? First idea that pops to mind is an event that will be activated when the instance is fully initialized, and off otherwise. Is there anything like that in ActionScript 3.0?

Thanks in advance!

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#2 greenvertex   Members   -  Reputation: 510

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Posted 09 August 2012 - 11:28 AM

If you're doing something like:

//...
private function loadMaze():void {
     _myMaze = new MazeType();
     _myMaze.findPath();
}
//...

This will not be prone to null reference. With some exceptions, code in AS3 all runs in a single thread. Where it doesn't:

//...
private function Init():void {
     _myMaze = new MazeType();
     _myMaze.loadMaze("myMaze.txt");
     _myMaze.findPath(); //null reference
}

//In MazeType class
plublic function loadMaze(mazeFile:String):void {
     var loader:Loader = new Loader();
     loader.contentLoaderInfo.addEventListener(Event.COMPLETE, mazeLoadComplete);
     //Other listeners such as IOErrorEvent.IO_ERROR
     loader.load(new URLRequest(mazeFile));
}

private function mazeLoadComplete(e:Event):void {
     //Check for errors, initialize and assign maze data.
}
//...

This code will fail if findPath() makes reference to the maze data before it has completed loading ("null reference") comment above. This is a totally contrived example but hopefully illustrates the point. If you're using something like a loader that dispatches events it's generally wise to only execute code on that object when those events are fired.

#3 prototypical   Members   -  Reputation: 301

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Posted 09 August 2012 - 01:03 PM

Greenvertex is spot on with one way this could be happening. But if that is not the case, you should verify your suspicions with some debugging techniques.

It's also possible that your process that initializes the mazes has simply not occurred yet. It's not far fetched that you might trigger something that relies on maze data before initializing the maze data. I've certainly done that type of thing before! :)

It's also possible that the initialization of the maze data has a bug, that leaves one of it's members null.

I encourage you to familiarize yourself with the debugger, and utilize traces/breakpoints in your code to track down issues like this quickly and efficiently.

#4 IronyGames   Members   -  Reputation: 134

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Posted 09 August 2012 - 02:42 PM

Solved it. Thanks!

For the record, it was a mixture of that 'contrived example' which was what I had at the moment and some problems with the algorithm itself. So thanks for the help, guys.

Edited by IronyGames, 09 August 2012 - 02:44 PM.





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