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behappy2
behappy2 wrote ...

2012/12/30

Dragging with the mouse

behappy2 behappy2

2012/12/30

#
Could someone please help me with making an object move when you click and drag it along.
nooby123 nooby123

2012/12/30

#
First make a variable that determines if it is dragging or not.
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boolean drag = false;
 
if(Greenfoot.mousePressed(this)) drag = true;
if(Greenfoot.mouseClicked(null)) drag = false;
 
if(drag) {
        // what ever you want to put in here
}
This'll work.
danpost danpost

2012/12/30

#
The following code will allow an object to be dragged by the mouse without having it go under other objects during the dragging procedure.
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/* add an instance boolean field to the class of the Actor object to be dragged */
private boolean isGrabbed;
 
/* in the 'act' method in the class of the Actor object to be dragged */
// check for initial pressing down of mouse button
if (Greenfoot.mousePressed(this) && !isGrabbed)
{
    // grab the object
    isGrabbed = true;
    // the rest of this block will avoid this object being dragged UNDER other objects
    World world = getWorld();
    MouseInfo mi = Greenfoot.getMouseInfo();
    world.removeObject(this);
    world.addObject(this, mi.getX(), mi.getY());
    return;
}
// check for actual dragging of the object
if ((Greenfoot.mouseDragged(this)) && isGrabbed)
{
    // follow the mouse
    MouseInfo mi = Greenfoot.getMouseInfo();
    setLocation(mi.getX(), mi.getY());
    return;
}
// check for mouse button release
if (Greenfoot.mouseDragEnded(this) && isGrabbed)
{
    // release the object
    isGrabbed = false;
    return;
}
behappy2 behappy2

2012/12/30

#
aha, so the world recreates the object, but where the mouse is! BUT it says --> if (Greenfoot.mousePressed(this) && !isGrabbed) is 'an illegal start of type'
danpost danpost

2012/12/30

#
You will have to show your class code (you probably put it in the wrong place and do not have your bracketing set proper).
behappy2 behappy2

2012/12/30

#
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import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
 
/**
 * Write a description of class something here.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class something extends Actor
{
    /* add an instance boolean field to the class of the Actor object to be dragged */
private boolean isGrabbed;
 
/* in the 'act' method in the class of the Actor object to be dragged */
// check for initial pressing down of mouse button
if (Greenfoot.mousePressed(this) && !isGrabbed)
{
    // grab the object
    isGrabbed = true;
    // the rest of this block will avoid this object being dragged UNDER other objects
    World world = getWorld();
    MouseInfo mi = Greenfoot.getMouseInfo();
    world.removeObject(this);
    world.addObject(this, mi.getX(), mi.getY());
    return;
}
// check for actual dragging of the object
if ((Greenfoot.mouseDragged(this)) && isGrabbed)
{
    // follow the mouse
    MouseInfo mi = Greenfoot.getMouseInfo();
    setLocation(mi.getX(), mi.getY());
    return;
}
// check for mouse button release
if (Greenfoot.mouseDragEnded(this) && isGrabbed)
{
    // release the object
    isGrabbed = false;
    return;
}
}
this is all my code
behappy2 behappy2

2012/12/30

#
and this is something
danpost danpost

2012/12/30

#
You need to enclose everything from line 14 on inside the 'act' method:
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public void act()
{
    // lines 14 through 41
}
behappy2 behappy2

2012/12/30

#
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import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
 
/**
 * Write a description of class something here.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class something extends Actor
{
    /* add an instance boolean field to the class of the Actor object to be dragged */
private boolean isGrabbed;
 
/**
 *
 */
public void act()
{
   /* in the 'act' method in the class of the Actor object to be dragged */
   // check for initial pressing down of mouse button
  if (Greenfoot.mousePressed(something) && !isGrabbed)
 {
    // grab the object
    isGrabbed = true;
    // the rest of something block will avoid something object being dragged UNDER other objects
    World world = getWorld();
    MouseInfo mi = Greenfoot.getMouseInfo();
    world.removeObject(something);
    world.addObject(something, mi.getX(), mi.getY());
    return;
}
// check for actual dragging of the object
if ((Greenfoot.mouseDragged(something)) && isGrabbed)
{
    // follow the mouse
    MouseInfo mi = Greenfoot.getMouseInfo();
    setLocation(mi.getX(), mi.getY());
    return;
}
// check for mouse button release
if (Greenfoot.mouseDragEnded(something) && isGrabbed)
{
    // release the object
    isGrabbed = false;
    return;
}
}
}
my if (Greenfoot.mousePressed(something) && !isGrabbed) doesnt find symbol- variable something
behappy2 behappy2

2012/12/30

#
do you have a dragging scenario that i could try out and edit into my own scen.?
nooby123 nooby123

2012/12/30

#
You can check out my scenario , but this is a smooth moving drag.
vonmeth vonmeth

2012/12/30

#
You shouldn't be replacing "this" with "something."
behappy2 behappy2

2012/12/30

#
ok
ZoeF ZoeF

2016/11/2

#
Ok i tryed to follow this as i kinda needed something similar. But i get a nullpointer exception on line 27. Any help and especialy explenation as to why would be realy appreciated.
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import greenfoot.*;
 
public class Cannon extends Towers
{
    private String cannonType;
    private Boolean isGrabbed;
     
    public Cannon()
    {
        this("0");
    }
     
    public Cannon(String newCannon)
    {
        setCannon(newCannon);
    }
     
    private void setCannon(String newCannon)
    {
        cannonType = newCannon;
    }
     
    public void act()
    {
        super.act();
        loadImage();
        if (Greenfoot.mousePressed(this) && !isGrabbed)
        {
            // grab the object
            isGrabbed = true;
            // the rest of this block will avoid this object being dragged UNDER other objects
            World world = getWorld();
            MouseInfo mi = Greenfoot.getMouseInfo();
            world.removeObject(this);
            world.addObject(this, mi.getX(), mi.getY());
            return;
        }
        // check for actual dragging of the object
        if (Greenfoot.mouseDragged(this) && isGrabbed)
        {
            // follow the mouse
            MouseInfo mi = Greenfoot.getMouseInfo();
            setLocation(mi.getX(), mi.getY());
            return;
        }
        // check for mouse button release
        if (Greenfoot.mouseDragEnded(this) && isGrabbed)
        {
            // release the object
            isGrabbed = false;
            return;
        }
    }
 
    private void loadImage()
    {
        GreenfootImage myCannon = new GreenfootImage("towers/cannon" + cannonType + ".png");
        setImage(myCannon);
    }
}
danpost danpost

2016/11/2

#
The field type on line 6 should be 'boolean' -- with a lowercase 'b'. Using an uppercase 'B' will have the field treated as an Object field reference of type Boolean instead of as a primitive type boolean field. As an object reference, its default value is 'null'; as a primitive field, it is assigned a value of 'false' by default. Also, all your multi-line comments should begin with '/**', using two asterisks. That way, at least in the postings here, some of your code lines will not look like comment lines because of their text color.
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