Question

I’m using actionscript 3.0 and Flash Professional CS5.5
I ran into a problem with instance objects which are not on the first frame.
My first frame is a menu and my second frame contains a TLF text field.
I have given the text field an instance name, let’s say “username_txt”.
Now if I turn off the “Automatically Declare Stage Instances” and do this in my main class

 public class MainClass extends MovieClip {

        public var username_txt:TLFTextField;

        public function MainClass() {
            username_txt.text = "anything";
        }
 }

I will receive a run time error stating that I try to access the property of a null object. (I have import all the necessary classes so that is not the problem)

This does not happen when I put the text right in the first frame though.

Any help?

Thanks in advance

Answer 1

As the text field has not yet been instantiated since the frame has not yet been reached, I’m unsure there is an elegant way to perform this task.

Perhaps a better model would be to decouple your data model from your views.

Create a singleton class to store data:

package
{

    public class ApplicationModel
    {

        /** Singleton instance. */
        private static var instance:ApplicationModel = new ApplicationModel();

        /** Return singleton instance. */
        public static function getInstance():ApplicationModel
        {
            return instance;
        }

        /** Data Model */
        public var username:String;

        /** Constructor as singleton enforcer */
        public function ApplicationModel()
        {
            if (instance)
                throw new Error("ApplicationModel is a singleton and can only be accessed through ApplicationModel.getInstance()");
        }

    }
}

Then from within anywhere such as keyframes or classes, you can get the instance of the object, implemented either as:

ApplicationModel.getInstance().username = "test";

Or a better practice would be:

var applicationModel:ApplicationModel = ApplicationModel.getInstance();
applicationModel.username = "test";

As per your example:

public class MainClass extends MovieClip {

    public var username_txt:TLFTextField;

    public function MainClass() {
        ApplicationModel.getInstance().username = "anything";
    }
}

Then, on the frame you need to update your TLFTextField (frame script of frame 2), you set the text based upon the model:

username_txt.text = ApplicationModel.getInstance().username

Your view will always update when needed.