That's my code if it might help you . { int bgWide = 15000; int bgHigh = 540; public static final int WIDE = 900; public static final int HIGH =540; public static final int CELL =1; private int gameTime; // number of game-time units elapsed private int gameTimer; Scroller scroller; Actor Megaman; Actor Mega2; private GreenfootSound bgMusic = new GreenfootSound("Gov.wav"); public Sky() { super( WIDE, HIGH, CELL, false); GreenfootImage bg = new GreenfootImage("Unknown.jpeg"); scroller = new Scroller(this, bg, bgWide, bgHigh); Megaman = new Megaman(); Mega2 = new Mega2(); addObject(Megaman, bgWide/2, bgHigh/2-230); addObject(Megaman, -100, 200); addObject(Mega2, bgWide/2, bgHigh/2+100); scroll(); Spawn(); } public void act() { if ((Megaman != null && Megaman.getWorld() == this) || (Mega2 != null && Mega2.getWorld() == this) ) scroll(); } private void scroll() { if (Megaman != null) { if (Megaman.getX()>Mega2.getX()) { int dsx = Megaman.getX()-WIDE/2; int dsy = Megaman.getY()-HIGH/2; scroller.scroll(dsx, dsy); } else { int dsx = Mega2.getX()-WIDE/2; int dsy = Mega2.getY()-HIGH/2; scroller.scroll(dsx, dsy); }} }

I tried it it still doesn't work. I think that the problem is that it disappears when it gets eaten so we can't usethe getX of Megaman or Mega2. (sorry for taking so long to answer btw)

Please show what you tried. (show act and scroll methods)

import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo) /** * Write a description of class Sky here. * * @author (your name) * @version (a version number or a date) */ public class Sky extends World { int bgWide = 15000; int bgHigh = 540; public static final int WIDE = 900; public static final int HIGH =540; public static final int CELL =1; private int gameTime; // number of game-time units elapsed private int gameTimer; Scroller scroller; Actor Megaman; Actor Mega2; private GreenfootSound bgMusic = new GreenfootSound("Gov.wav"); public Sky() { super( WIDE, HIGH, CELL, false); GreenfootImage bg = new GreenfootImage("Unknown.jpeg"); scroller = new Scroller(this, bg, bgWide, bgHigh); Megaman = new Megaman(); Mega2 = new Mega2(); addObject(Megaman, bgWide/2, bgHigh/2-230); addObject(Mega2, bgWide/2, bgHigh/2+100); scroll(); Spawn(); } public void act() { if ((Megaman != null && Megaman.getWorld() == this) || (Mega2 != null && Mega2.getWorld() == this) ) scroll(); //if (Megaman.getWorld() != null) { gameTimer = (gameTimer + 1) % 60; // adjust 6 to suit if (gameTimer == 0) gameTime++; } //else {addObject(gameTime,100,1000);} } private void scroll() { if (Megaman != null && Mega2!= null) { if (Megaman.getX()>Mega2.getX()) { int dsx = Megaman.getX()-WIDE/2; int dsy = Megaman.getY()-HIGH/2; scroller.scroll(dsx, dsy); } else { int dsx = Mega2.getX()-WIDE/2; int dsy = Mega2.getY()-HIGH/2; scroller.scroll(dsx, dsy); }}

I also tried with if (Megaman != null && Mega2!= null) { both aren't working That's the error message if it might help you. java.lang.IllegalStateException: Actor not in world. An attempt was made to use the actor's location while it is not in the world. Either it has not yet been inserted, or it has been removed. at greenfoot.Actor.failIfNotInWorld(Actor.java:713) at greenfoot.Actor.getX(Actor.java:165) at Sky.scroll(Sky.java:51) at Sky.act(Sky.java:39) at greenfoot.core.Simulation.actWorld(Simulation.java:573) at greenfoot.core.Simulation.runOneLoop(Simulation.java:506) at greenfoot.core.Simulation.runContent(Simulation.java:193) at greenfoot.core.Simulation.run(Simulation.java:183)

Yes. Line 39 ensures that one of the two actors is in the world -- not both. However, line 51 requires that both be in the world. Line 50 does nothing as far as ensuring they are in the world; it only ensures that both actors exist (whether in the world or not). Change line 39 to simply: Then as a first course of action in the scroll method, determine if both, only one or neither actor are in the world. There are a total of 4 cases: (0) neither are in world (1) only Megaman is in world (2) only Mega2 is in world (3) both are in world I numbered them that way for a reason. Assigning (1) and (2) that way allows the sum to be (3); and neither, being not (1) and not (2), makes sense to be (0). So: Now you can scroll with respect to leader.

And where should I put it in the scroll class ?

I wrote: (not class). The Scroll class should never be modified.

I wrote it like this, what should i correct ? private void scroll() { int men = 0; if (Megaman != null && Megaman.getWorld() != null) men += 1; if (Mega2 != null && Mega2.getWorld() != null) men += 2; if (men == 0) return; Actor leader = null; if (men < 3) leader = men == 1 ? Megaman : Mega2; else{ leader = Megaman.getX() >= Mega2.getX() ? Megaman : Mega2; if (Megaman.getX()>Mega2.getX()) { int dsx = leader-WIDE/2; int dsy = leader()-HIGH/2; scroller.scroll(dsx, dsy); }} }

Remove the last if structure around the scrolling code.

Okay it doesn't crash anymore but it doesn't follow Mega 2 if Megaman dies That's how i wrote it : private void scroll() { int men = 0; if (Megaman != null && Megaman.getWorld() != null) men += 1; if (Mega2 != null && Mega2.getWorld() != null) men += 2; if (men == 0) return; Actor leader = null; if (men < 3) leader = men == 1 ? Megaman : Mega2; else{ leader = Megaman.getX() >= Mega2.getX() ? Megaman : Mega2; { int dsx = leader.getX()-WIDE/2; int dsy = 270; scroller.scroll(dsx, dsy); }} }