如果我知道尸体，如何将精灵附着到box2d尸体上？

Question

After collision detection I can get the bodies that collided, but how can I get the sprites attached to these bodies so I can remove them from the scene also?

For example if I had a body (player) this body collided with another body (enemy), I can get which bodies collide from the contact listener like this:

pContact.getFixtureA().getBody()
pContact.getFixtureB().getBody()

So if we assume that we have a lot of enemies how can I get the exact sprite attached to each one of the bodies so I can remove them?

Answer 1

disclaimer: My experience is with Cocos2d/Box2D in iOS, but should be similar in Android.

Typically, when using Box2D bodies and sprites you set the UserData property of the Body Definition with the sprite. Example:

setting userData:

bodyDef.UserData = sprite;

retrieving sprite after contact:

enemySprite = pContact.getFixtureA().getBody().GetUserData()

Answer 2

You should have an Enemy class, that has its Body and Sprite . If you have a body that had a contact with an another body, you can iterate over the list of your Enemy objects to find whose body was that by simply comparing them. Then you can easily get this Enemy object's sprite. Hope I've explained my idea clear enough.

Answer 3

After read this thread on AndEngine forums, this is my solution:

Create a new "UserData" class:

public class UserData implements Serializable {

    private static final long serialVersionUID = 1L;

    String mString;
    Object mObject;

    public UserData(){}

    public UserData(String string, Object object) {
        this.mString = string;
        this.mObject = object;
    }

    public String getString() {
        return mString;
    }

    public Object getObject() {
        return mObject;
    }
}

Set the UserData of all your body s with the UserData class:

body.setUserData(new UserData("enemy", CustomSprite));

Then you can detect the collision and get your CustomSprite:

if (((UserData) x1.getBody().getUserData()).getString().equals("enemy") && ((UserData) x2.getBody().getUserData()).getString().equals("bullet")) {
    CustomSprite myEnemySprite = (CustomSprite) ((UserData) x1.getBody().getUserData()).getObject();
    myEnemySprite.die();
}

Answer 4

enemy.setUserData(new Object[]{"enemy",enemySprite/*,... And other objects as user data if you wish */})

And while checking:

final Object[] x1 = (Object[]) contact.getFixtureA().getBody().getUserData();
final Object[] x2 = (Object[]) contact.getFixtureB().getBody().getUserData();

Doing something:

if(x1[0].equals("This is the tag for the enemy"))
x2[1].playerhascollidedwithyouandyouhavetodosomething();