AS3 KeyCode Reader

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It’s one of the most well known bits of KeyCode gibberish out there and has spawned all sorts of web fun. The Konami Code was my first experience with a cheat code when I learned it for the 1988 game Contra on NES. Facebook made some noise when they implemented a hidden Konami code Easter Egg on their site back in 2009. It’s a bit of nostalgic fun, really.

My first encounter with KeyCode reading was thanks to Guy Wyatt down at Moxie Interactive back in 2007 or 2008 when he showed me an implementation he’d done for a web-game that he wanted to add cheat codes into. I’ve written a few versions of my own since then, but this latest is the simplest and most flexible.

My KeyCodeReader class is the workhorse here. When you add it to an application, you create an instance and pass it a reference to the stage. This is necessary because keycode capturing has to happen via a stage listener. Once you’ve instantiated the class, you can start adding matching codes. The codes are arrays of keycode values. These are not ASCII values, necessarily. They’re determined by the physical key on the keyboard. That can have some strange effects for international users, or users like yours truly who enjoy the benefits of the Dvorak keymap.

Now coming up with these codes might seem like a difficult task, but as you’ll see in my example app, it’s really quite easy. Other implementations I’ve built have used ASCII methods and actual strings, which is honestly easier to develop, but extremely limited. You can’t map the arrow keys with ASCII, for instance. That’s just a shame.

This class doesn’t do anything fancy beyond allowing you to define codes and test to see if they’ve been matched, but it does give you some helpful tweaking tools. By default the user has 300 milliseconds between character presses to enter the code. If you have a slow-typing audience, this can be changed in the constructor. Also, it’s important to note that this will not match overlapping codes. For instance, if you define ABCD and ABCDE both as matchable codes, only ABCDE will be tested. Since ABCD is just an unfinished version of ABCDE, it is basically overwritten by the more “full” code. There were several ways I could have handled that issue, and this wasn’t necessarily “right”, but that’s what happens to lab projects!

Finally, when a code is matched, it will dispatch a KeyCodeEvent with a key property that holds the matched code array. You can use this array for any fancy switching to figure out what you want to do next. Here’s the Event class:


In the linked folder I’ve created a sample project with an implemented KeyCodeReader class and a couple simple match codes. It is also a helpful tool for figuring out what the codes for each key are.

Finally, it’s worth noting several things severely lacking in my implementation. You know they’re serious flaws since they even got comments in the code.

  1. I haven’t added any special support for held keys, like Control, Alt or Shift. Right now they’re processed just like any other key presses in a sequence. It’s really not that much work to fix the omission, but I’ve yet to have a need for it, so there you go.
  2. I haven’t added the method for removing a match code. It’s stubbed out, but again, I’ve never had the need.
  3. There’s almost zero error handling in here. If you add a match code that’s not integer based, or any number of other simple things, the class will totally blow up. So, um, enjoy that!

Source & Example

By the way, in case you want to implement the Konami Code yourself, here’s the character array: [38, 38, 40, 40, 37, 39, 37, 39, 66, 65, 13]

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