Libgdx null指針

Question

我正在使用Box2D跳轉並運行遊戲，並希望玩家在碰到尖峯時被傳送到開始位置，但當他遇到尖峯時，我會得到空指針異常。

繼承人我跟類：

public class WorldContactListener implements ContactListener { 

Player player; 

@Override 
public void beginContact(Contact contact) { 
    Fixture fixA = contact.getFixtureA(); 
    Fixture fixB = contact.getFixtureB(); 
    player = new Player(); 

    int cDef = fixA.getFilterData().categoryBits | fixB.getFilterData().categoryBits; 

    switch (cDef) { 
     case HardwareRunner.PLAYER_BIT | HardwareRunner.BRICK_BIT: 
     case HardwareRunner.PLAYER_BIT | HardwareRunner.SPIKE_BIT: 
      player.die(); 

    } 
} 

而且我的繼承人播放器類的部分：

public void definePlayer(){ 
    bdef.position.set(32/runner.PPM, (6 * 32)/runner.PPM); 
    bdef.type = BodyDef.BodyType.DynamicBody; 
    b2body = world.createBody(bdef); 

    FixtureDef fdef = new FixtureDef(); 
    PolygonShape shape = new PolygonShape(); 
    Vector2[] vertice = new Vector2[4]; 
    vertice[0] = new Vector2(-13, 13).scl(1/runner.PPM); 
    vertice[1] = new Vector2(13, 13).scl(1/runner.PPM); 
    vertice[2] = new Vector2(13, -13).scl(1/runner.PPM); 
    vertice[3] = new Vector2(-13, -13).scl(1/runner.PPM); 
    shape.set(vertice); 
    shape.getRadius(); 
    fdef.filter.categoryBits = HardwareRunner.PLAYER_BIT; 
    fdef.filter.maskBits = 
      HardwareRunner.GROUND_BIT | 
      HardwareRunner.COIN_BIT | 
      HardwareRunner.BRICK_BIT | 
      HardwareRunner.ENEMY_BIT | 
      HardwareRunner.SPIKE_BIT | 
      HardwareRunner.ENEMY_HEAD_BIT | 
      HardwareRunner.ITEM_BIT; 

    fdef.shape = shape; 
    fdef.friction = .1f; 
    b2body.createFixture(fdef).setUserData(this); 
    fdef.isSensor = true; 

    b2body.createFixture(fdef).setUserData(this); 
} 

public void die() { 
    world.destroyBody(b2body); 

    bdef.position.set(32/runner.PPM, (6 * 32)/runner.PPM); 
    bdef.type = BodyDef.BodyType.DynamicBody; 
    b2body = world.createBody(bdef); 

    FixtureDef fdef = new FixtureDef(); 
    PolygonShape shape = new PolygonShape(); 
    Vector2[] vertice = new Vector2[4]; 
    vertice[0] = new Vector2(-13, 13).scl(1/runner.PPM); 
    vertice[1] = new Vector2(13, 13).scl(1/runner.PPM); 
    vertice[2] = new Vector2(13, -13).scl(1/runner.PPM); 
    vertice[3] = new Vector2(-13, -13).scl(1/runner.PPM); 
    shape.set(vertice); 
    shape.getRadius(); 
    fdef.filter.categoryBits = HardwareRunner.PLAYER_BIT; 
    fdef.filter.maskBits = 
      HardwareRunner.GROUND_BIT | 
        HardwareRunner.COIN_BIT | 
        HardwareRunner.BRICK_BIT | 
        HardwareRunner.ENEMY_BIT | 
        HardwareRunner.SPIKE_BIT | 
        HardwareRunner.ENEMY_HEAD_BIT | 
        HardwareRunner.ITEM_BIT; 

    fdef.shape = shape; 
    fdef.friction = .1f; 
    b2body.createFixture(fdef).setUserData(this); 
    fdef.isSensor = true; 

    b2body.createFixture(fdef).setUserData(this); 
} 

和錯誤是：

Exception in thread "LWJGL Application" java.lang.NullPointerException 
at de.tobls.hardwarerunner.Sprites.Player.die(Player.java:223) 
at de.tobls.hardwarerunner.Tools.WorldContactListener.beginContact(WorldContactListener.java:27) 
at com.badlogic.gdx.physics.box2d.World.beginContact(World.java:982) 
at com.badlogic.gdx.physics.box2d.World.jniStep(Native Method) 
at com.badlogic.gdx.physics.box2d.World.step(World.java:686) 
at de.tobls.hardwarerunner.Screens.PlayScreen.update(PlayScreen.java:112) 
at de.tobls.hardwarerunner.Screens.PlayScreen.render(PlayScreen.java:127) 
at com.badlogic.gdx.Game.render(Game.java:46) 
at de.tobls.hardwarerunner.HardwareRunner.render(HardwareRunner.java:71) 
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:215) 
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:120) 

誰能幫助我？

Answer 1

首先你不應該用來破壞異步方法中的世界物品 - 注意接觸偵聽器的方法是異步的。

破壞身體OD來標記它，然後摧毀正義之前world.update（）

//in asynchronous method 
    body.setUserData("DESTROY"); 

    //when rendering 
    for(Body body : world.getBodies()) 
      if(body.getUserData().equals("DESTROY")) world.destroyBody(body); 

在此之上但正確的方法 - 我看你什麼都不做但移動身體時，死了那麼爲什麼不使用的setTransform方法，然後

body.setTransform(new Vector2(newX, newY), body.getAngle()); 

而是再次去除身體和創造它的一個新的位置