Greenfoot

danpost

2014/6/6

#

OK. Change it back to 'public BackgroundLvL1()'. You will not be passing anything to this world. You will be passing this world through other worlds.

SAAEngineer

2014/6/6

#

Will telll you the outcome as soon as i can!

SAAEngineer

2014/6/6

#

I tried changing it back but now i get an error in Countdown_Go , where it has to launch the world:

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Countdown1 here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Countdown_Go extends World
{
    public int countdowndelay = 40;
    public int countdownteller = countdowndelay;
    GreenfootSound go = new GreenfootSound("go.mp3");
    private World previousWorld;  
    // add instance field
    /**
     * Constructor for objects of class Countdown1.
     * 
     */
    public Countdown_Go()
    {    
        // Create a new world with 600x400 cells with a cell size of 1x1 pixels.
        super(480, 800, 1);
        go.play();
    }
    public void act(){
       if (countdownteller > 0) {
           countdownteller--;
    }
    if (countdownteller == 0) {
           Greenfoot.setWorld(previousWorld); 
    }
   
}}

On rule 31 i get the error: java.lang.NullPointerException: The given world cannot be null.

danpost

2014/6/6

#

This is one of the world you need to pass the BackgroundLvL1 world to:

// change line 20 to
public Countdown_Go(World world)
// and insert at line 24
previousWorld = world;

Your Countdown_1 world will have to pass it using 'new Countdown_go(previousWorld)' when creating this world.

SAAEngineer

2014/6/6

#

the transition from countdown_1 to countdown_go is perfectly fine, it's the transition from Countdown_go to BackgroundLvL1 that's the problem

danpost

2014/6/6

#

The transition may be fine; but, the needed field value is not!

SAAEngineer

2014/6/6

#

then i get the error in Countdown_1 and if we change that we'll probably get it in Countdown_2 aswell.

danpost

2014/6/6

#

The BackgroundLvL1 class should instantiate a Countdown3 world object with 'new Countdown3(this)', which passes itself to the Countdown3 class object created; the Countdown3 object should store the value and pass it to the Countdown2 world object when it is created; this world object should do the same to pass it to Countdown1 and then to Countdown_go, where the passed world object will finally be returned from.

danpost

2014/6/6

#

SAAEngineer wrote...

then i get the error in Countdown_1 and if we change that we'll probably get it in Countdown_2 aswell.

What error are you getting and what is the code you are using there.

SAAEngineer

2014/6/6

#

danpost wrote...

The BackgroundLvL1 class should instantiate a Countdown3 world object with 'new Countdown3(this)', which passes itself to the Countdown3 class object created; the Countdown3 object should store the value and pass it to the Countdown2 world object when it is created; this world object should do the same to pass it to Countdown1 and then to Countdown_go, where the passed world object will finally be returned from.

Can you give me the exact lines pleas?

danpost

2014/6/6

#

SAAEngineer wrote...

< Quote Omitted > Can you give me the exact lines pleas?

If you show the classes, I can point out the lines.

SAAEngineer

2014/6/6

#

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Countdown1 here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Countdown3 extends World
{
    public int countdowndelay = 40;
    public int countdownteller = countdowndelay;
    GreenfootSound beep = new GreenfootSound("beep.mp3");
    /**
     * Constructor for objects of class Countdown1.
     * 
     */
    public Countdown3()
    {    
        // Create a new world with 600x400 cells with a cell size of 1x1 pixels.
        super(480, 800, 1);
        beep.play();
    }
    public void act(){
       if (countdownteller > 0) {
           countdownteller--;
    }
    if (countdownteller == 0) {
           Greenfoot.setWorld(new Countdown2()); 
    }
}}

All Countdown classes are the same

danpost

2014/6/6

#

Add 'World world' inside the parenthesis of line 18 (in all Countdown classes). Insert 'previousWorld = world;' at line 23 (inside the constructor block of all Countdown classes). Insert 'private World previousWorld;' at line 14 (in all Countdown classes).

SAAEngineer

2014/6/7

#

Okay i added everything but now in BackgroundLvL1 i get the error :

on this line:

Greenfoot.setWorld(new Countdown3());

danpost

2014/6/7

#

Again, you need to pass the BackgroundLvL1 world on to the next world.

Greenfoot.setWorld(new Countdown3(previousWorld));

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