How to navigate in a circle

the title might be not very descriptive but i couldn't think of a better one.

The problem is as follows: I have one screen (ScreenOne) with a link to another screen (ScreenTwo). On the ScreenTwo is a link back to ScreenOne.

I implemented this via custom 开发者_开发问答RichTextFields and a custom ChangeListener.

Now the problem is that i keep getting a StackOverflowError! Is there any way to navigate back and forth in that way?

regards matt

public class MyApp extends UiApplication
{
    public static void main(String[] args)
    {
        MyApp theApp = new MyApp();       
        theApp.enterEventDispatcher();
    }

    public MyApp()
    {
        ScreenOne so = ScreenProvider.getInstance().getScreenOne();
        so.initialize();
        ScreenProvider.getInstance().getScreenTwo().initialize();
        pushScreen(so);
    }    
}

public class ScreenOne extends MainScreen {
    MyTextField link;

    public ScreenOne() {
        link = new MyTextField("FirstScreen");
        add(link);
    }

    public void initialize(){
        link.setChangeListener((FieldChangeListener) new MyFieldChangeListener(ScreenProvider.getInstance().getScreenTwo()));
    }
}

public class ScreenTwo extends MainScreen {
    MyTextField link;

    public ScreenTwo() {
        link = new MyTextField("SecondScreen");
        add(link);
    }

    public void initialize(){
        link.setChangeListener((FieldChangeListener) new MyFieldChangeListener(ScreenProvider.getInstance().getScreenOne()));
    }
}

public class MyFieldChangeListener implements FieldChangeListener {

    private Screen nextScreen;

    public MyFieldChangeListener(Screen nextScreen) {
        this.nextScreen = nextScreen;
    }

    public void fieldChanged(Field field, int context) {
        UiApplication.getUiApplication().pushScreen(nextScreen);
    }
}

public class MyTextField extends RichTextField {
    public MyTextField() {
        super();
    }

    public MyTextField(String text) {
        super(text);
    }

    protected boolean touchEvent(TouchEvent message) {
        if (TouchEvent.CLICK == message.getEvent()) {
            FieldChangeListener listener = getChangeListener();
            if (null != listener)
                listener.fieldChanged(this, 1);
        }
        return super.touchEvent(message);
    }
}

public class ScreenProvider {
    private static ScreenProvider instance = null;

    private ScreenProvider(){}

    public static ScreenProvider getInstance() {
        if (instance == null) {
            instance = new ScreenProvider();
        }
        return instance;
    }

    private ScreenOne screenOne = new ScreenOne();
    private ScreenTwo screenTwo = new ScreenTwo();

    public ScreenOne getScreenOne() {
        return screenOne;
    }

    public ScreenTwo getScreenTwo() {
        return screenTwo;
    }
}

The constructor of ScreenOne creates a ScreenTwo instance, and the constructor of ScreenTwo creates a ScreenOne instance. You have an infinite loop here.

Regarding revision 5 of this question:

new ScreenProvider() -> new ScreenOne() -> ScreenProvider.getInstance() -> new ScreenProvider() -> ...

still infinite. Again, the problem is that you're trying to setup a cycle via object constructors. You need to create the objects first, then assign the next and previous.

Regarding revision 4 of this question:

getScreenOne() -> new ScreenOne() -> getScreenTwo() -> new ScreenTwo() -> getScreenOne() -> newScreenOne() -> ...

you still have an infinite loop, because the constructors are trying to store an instance of each other. You need to construct the objects first, then add the cyclic references.

In your ScreenProvider you don't need to make screen1/screen2 static -- they're members of the singleton instance.

Outside of that the other problem I see in this current version is that you're going to be pushing a screen onto the stack -- that's already on the stack. Try popping the prior screen first.

That overflow error is likely the result of an infinite loop caused by constantly jumping from ScreenOne and ScreenTwo. Could you describe what you actually would want to accomplish and/or show a snippet of code?