Greenfoot

kevv

2012/11/11

#

Hi, does anyone have idea how to improve my code where the arrow hits the dragon. It only works when hitting the exact middle of the dragon image.

    public void kill()
    {
        Actor arrow;
        arrow = getOneObjectAtOffset(0, 0, Arrow.class);
        if (arrow != null)
        {
            setImage("dead.png");
            pause();

http://www.greenfoot.org/scenarios/6523 here is the scenario, don't currently want to make the code public.

erdelf

2012/11/11

#

change line 4 to this:

arrow = getOneIntersectingObject(Arrow.class);

kevv

2012/11/11

#

Thanks mate. Now I got a new problem. My score counter code:

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

/**
 * Write a description of class Counter here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Counter extends Actor
{
    private int score;
    
    public Counter()
    {
        score = 0;
        setImage (new GreenfootImage(200, 30));
        update();
    }
    
    public void addScore()
    {
        score++;
        update();
    }
    
    public void update()
    {
        GreenfootImage img = getImage();
        img.clear();
        img.setColor(Color.WHITE);
        img.drawString("Dragons killed: " + score, 20, 30);
    }
}

The part from the dragon class when it should add score:

    public void kill()
    {
        Actor arrow;
        arrow = getOneIntersectingObject(Arrow.class);  
        if (arrow != null)
        {
            setImage("dead.png");
            pause();
            counter.addScore();

In the world:

        Dragon dragon = new Dragon(counter);

and in the top:

    private Counter counter;

Error I get:

java.lang.NullPointerException
	at Dragon.kill(Dragon.java:104)
	at Dragon.act(Dragon.java:38)
	at greenfoot.core.Simulation.actActor(Simulation.java:565)
	at greenfoot.core.Simulation.runOneLoop(Simulation.java:523)
	at greenfoot.core.Simulation.runContent(Simulation.java:213)
	at greenfoot.core.Simulation.run(Simulation.java:203)

What am doing wrong? :)

SPower

2012/11/11

#

This is probably wrong:

counter.addScore();

you got a null pointer exception:

java.lang.NullPointerException

which means you're using an object which is null. For more about exceptions, follow this course.

kevv

2012/11/11

#

Sorry, i'm sure i should actually follow your course for my own gain, but too tired and have to get things done. Have added a counter like that before in another game, can see what is different this time it does not work. Would be very grateful for some help as if you talked to a very stupid person. ;) (maybe I am)

SPower

2012/11/11

#

Add this code before using the counter (before the addScore method)

if (counter == null)
    counter = getWorld().getObjects(Counter.class).get(0);
// now you can use the counter!

kevv

2012/11/11

#

            if (counter == null)  
            counter = getWorld().getObjects(Counter.class).get(0);  
            counter.addScore();

highlights the 0 in the end and says incompatible types

erdelf

2012/11/11

#

change the line to:

counter = (Counter)getWorld().getObjects(Counter.class).get(0);

kevv

2012/11/11

#

Ok now it works but the counter keeps on increasing. But I wanna figure this one out myself. :) Thank you very much erdelf! // sorry forgot to thank SPower for his help!

kevv

2012/11/11

#

If I would like to use getObjectsInRange instead of getOneIntersectingObject(Arrow.class); how should it look like? Greenfoot summary says: getObjectsInRange(int radius, java.lang.Class cls) Return all objects within range 'radius' around this object. So I tried: arrow = getObjectsInRange(100, Arrow.class); It says incompatible types. Reason Why i want to change it is that the gif is bigger than the actual dragon.

danpost

2012/11/11

#

The method 'getObjectsInRange' does not return an Object (by itself), but a List object that may or may not contain any objects. Since you cannot set a List object to a field that is declared to hold an Arrow object, you get your error. You can use

if (!getObjectsInRange(100, Arrow.class).isEmpty())
{
    arrow = (Arrow) getObjectsInRange(100, Arrow.class).get(0);
    // etc.

to get a reference to the arrow object.

kevv

2012/11/12

#

    private void newDragon()
    {
        if (alive == false) 
        { 
            alive = true;
            getWorld().addObject (new Dragon (counter), 0, 400);  
            
            }
        }

http://www.greenfoot.org/scenarios/6523 Tried so many different ways, cannot figure out why one dragon won't be created. : /

kevv

2012/11/12

#

    private void newDragon()
    {
        if (alive == false && dragonCreated == false) 
        { 
            alive = true;
            getWorld().addObject (new Dragon (counter), 0, 400);  
            dragonCreated = true;
            }
        }

This keeps it kinda under control but still not the way I need it. One dies another appears.

danpost

2012/11/12

#

How about something like

if (getWorld().getObjects(Dragon.class).isEmpty())

OH, and forget about all the booleans.

kevv

2012/11/12

#

    private void newDragon()
    {
        if (getWorld().getObjects(Dragon.class).isEmpty())  
        { 
            getWorld().addObject (new Dragon (counter), 0, 400);  
            }
        }

Like this nothing happens. :)

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