AC3 "The base specified is a native class..."??

Question

Hello, I'm having a problem with linking one of my symbols to my document class.  I went under Properties in my symbol drop-down list and put the correct base class in their (flash.display.MovieClip), however it keeps giving me this error when I click to see if it goes through: The base specified is a native class and will be defined in the player at runtime.  It cannot be edited".  When I went back to check my code, it had the correct "public class DocumentClass extends MovieClip" under "import flash.display.MovieClip".  What am I doing wrong?  I'm pretty new to Flash and AC3..
package
    import flash.display.MovieClip;
    public class DocumentClass extends MovieClip
        public var playScreen:AvoiderGame;
        public function DocumentClass()
            playScreen = new AvoiderGame();
            addChild( playScreen );

Answer 1

If your Library symbols have AvoiderGame in their base class field, then the "Class" field should automatically be filled in with the name of the symbol, unless you already filled it in with something else. If you filled it in with something else, just copy the name of the symbol and paste it into the Class field and paste your custom Class into the Base Class field (the one at the bottom). When you use the Base Class field, it allows you to use your custom Class for multiple Library Symbols, because the Class name being used to form the linkage is the other field (Class).
To use a symbol, you'd do something like:
public class DocumentClass extends MovieClip {
     protected var game:AvoiderGame;
     public function DocumentClass() {
          super();
          game = new YourLibrarySymbolName() as AvoiderGame;
          addChild(game);
Note that at this point it sounds like you're totally not following the tutorial, because Michael said pretty clearly that he was using the AvoiderGame Class as his Document Class, but you know--whatever. It's just not really possible to give you very good help, because it's impossible to determine if you've diverged from the tutorial on purpose, because you know what you're doing, on purpose, because you think you know what you're doing, but don't, or accidentally, because you don't understand what you're reading.