public interface IGameView {

    /**
     * @return game data object
     */
    public Properties getGameData();

    /**
     * @param data game data object
     */
    public void setGameData(Properties data);
    
    /**
     * @param setter Instance of the program setting the active view
     */
    public void setViewSetter (IViewSetter setter);
}

public class MainActivity extends Activity implements IViewSetter {
    // Die Spielstandsdaten- Neudeutsch: Geschäftsobjekt
    Properties gameData = new Properties();    

      public void setView(String, viewName) {
       ...
        // mache den ViewSetter bekannt
        view.setViewSetter(this);
        // mache der View den Spielstand bekannt.
        view.setGameData(gameData);
        // setze die neue View
        setContentView ((View) view);
    }

public class MainMenu extends LinearLayout implements IGameView,
    OnClickListener {
    IViewSetter setter = null;

    Properties gameData = new Properties();

    Button startGame = null;
    Button loadGame = null;
    Button saveGame = null;
    Button exit = null;

    private Button createMenuButton(String name) {
    Button b = new Button(getContext());
    b.setText(name);
    b.setVisibility(VISIBLE);
    b.setPadding(2, 2, 2, 2);
    b.getBackground().setAlpha(0x80);
    b.setClickable(true);
    b.setOnClickListener(this);
    this.addView(b);

    return b;
    }

    public MainMenu(Context context) {
    super(context);
    try {
        // set visibility
        this.setVisibility(VISIBLE);
        // gravity is bottom
        this.setOrientation(VERTICAL);
        this
            .setGravity(Gravity.CENTER_VERTICAL
                | Gravity.CENTER_HORIZONTAL);

        startGame = this.createMenuButton("Start Game");
        loadGame = this.createMenuButton("Load Game");

        // wenn Daten im Spieleobjekt enthalten sind,
        // stelle den save-button dar
        if (!this.gameData.isEmpty()) {
        saveGame = this.createMenuButton("Save Game");
        }
        exit = this.createMenuButton("Exit");

    } catch (IOException e) {
        e.printStackTrace();
    }
    }

    @Override
    public Properties getGameData() {
        return gameData;
    }

    @Override
    public void setGameData(Properties data) {
        this.gameData = data;
    }

    @Override
    public void setViewSetter(IViewSetter setter) {
        this.setter = setter;
    }

    @Override
    public void onClick(View v) {
    Log.d("TraderGame", "item click");
    if (v == startGame) {
        this.setter.setView("gameloop");
    } else if (v == loadGame) {
        this.setter.setView("loadgame");
    } else if (v == saveGame) {
        this.setter.setView("savegame");
    } else if (v == exit) {
        this.setter.setView("exit");
    }

    }

}

public abstract class FileListView extends LinearLayout implements IGameView,
    OnItemClickListener, OnClickListener {
    protected IViewSetter setter = null;
    protected Properties gameData = new Properties();
    protected File directory = null;

    protected ListView list = null;
    protected EditText filename = null;
    protected Button go = null;

    /**
     * @param context
     */
    public FileListView(Context context) {
    super(context);

    // Savegame-Verzeichnis erstellen
    createDirectory(context);

    // set visibility
    this.setVisibility(VISIBLE);
    // gravity is bottom
    this.setOrientation(VERTICAL);
    this.setGravity(Gravity.TOP | Gravity.LEFT);
    
    LinearLayout view2 = new LinearLayout(context);
    view2.setOrientation(HORIZONTAL);
    view2.setGravity(Gravity.LEFT);
    
    // add filename textfield
    this.filename = new EditText(context);
    this.filename.setWidth(250);
    view2.addView(filename);
    
    // add run button
    this.go = new Button(context);
    this.go.setText("go");
    this.go.setOnClickListener(this);
    view2.addView(go);
    
    this.addView(view2);
    
    // add ListView
    this.list = new ListView(context);
    this.list.setId(R.id.ListView01);
    this.list.setOnItemClickListener(this);
    String fileList[] = directory.list();

    
    this.list.setAdapter(new ArrayAdapter<String>(context, android.R.layout.simple_list_item_1, fileList));
    
    this.addView(this.list);
    }
   

    /**
     * create data directory
     * 
     * @param context
     */
    private void createDirectory(Context context) {
    directory = new File("/sdcard/."
        + context.getResources().getString(R.string.app_name));
    // Erstelle das Unterverzeichnis für die Savegames, falls nötig
    if (!directory.isDirectory()) {
        directory.mkdir();
    }
    }

    /*
     * (non-Javadoc)
     * 
     * @see de.docjunior.gameengine.IGameView#getGameData()
     */
    @Override
    public Properties getGameData() {
    return this.gameData;
    }

    /*
     * (non-Javadoc)
     * 
     * @see de.docjunior.gameengine.IGameView#setGameData(java.util.Properties)
     */
    @Override
    public void setGameData(Properties data) {
    this.gameData = data;

    }

    /*
     * (non-Javadoc)
     * 
     * @see
     * de.docjunior.gameengine.IGameView#setViewSetter(de.docjunior.gameengine
     * .IViewSetter)
     */
    @Override
    public void setViewSetter(IViewSetter setter) {
    this.setter = setter;
    }

    @Override
    public void onItemClick(AdapterView<?> arg0, View arg1, int item, long arg3) {
    this.filename.setText(this.list.getItemAtPosition(item).toString());
    }

    /**
     * gets the created file
     * @return
     */
    protected File getFile() {
    File f = null;
    if (!this.filename.getText().equals("")) {
        String dir = this.directory.getAbsolutePath();
            dir += "/" + this.filename.getText();
            dir.replace(" ", "_");
        Log.d(getContext().getString(R.string.app_name), "File:" + dir );    
        f = new File (dir);    
    }
    return f;
    }
}

public class LoadGame extends FileListView {

    /**
     * @param context
     */
    public LoadGame(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
    }

    /* (non-Javadoc)
     * @see android.view.View.OnClickListener#onClick(android.view.View)
     */
    @Override
    public void onClick(View v) {
    if (v == this.go) {
        InputStream is;
        try {
        is = new FileInputStream(getFile());
        this.gameData.load(is);
        this.setter.setView("gameloop");
        } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
    }

    }

}

public class SaveGame extends FileListView {

    /**
     * @param context
     */
    public SaveGame(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
    }

    /*
     * (non-Javadoc)
     * 
     * @see android.view.View.OnClickListener#onClick(android.view.View)
     */
    @Override
    public void onClick(View v) {
    if (v == this.go) {
        OutputStream os;
        try {
        os = new FileOutputStream(getFile());
        this.gameData.store(os, "save game at" + new Date());
        this.setter.setView("mainmenu");
        } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
    }
    }

}

    public void setGameData(Properties gameData) {
    // TODO Auto-generated method stub
    this.gameData = gameData;
    if (gameData.isEmpty()) {
        InputStream in;
        try {
        in = getContext().getAssets().open("newgame.properties");
        gameData.load(in);
        } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
    }
    }