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;
    }
}

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

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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.

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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.

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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?