当 Sprites 到达特定位置时，我该如何移除它们？

Question

我的 Sprite 是随机生成的，生成后向上移动，直到它们到达某个位置，然后它们应该被移除。这就是我一直在尝试做的，但我总是遇到错误。

//this method is called at random time
 public void newEnemy(){
        Sprite enemy= Pools.obtain(Sprite.class);
        enemy.set(enemySpr);
        enemy.setPosition(200,150);
        enemies.add(enemy);
    }



//removing the enemy
 while (enemyIterator.hasNext()){
  Sprite nextEnemy=enemyIterator.next();//<--error here,this is line 66  
           if(enemySpr.getY()+enemySpr.getHeight()>=treeObj.treeSpr.getY()){
               removeEnemy(nextEnemy);
           }
       }



//removeEnemy method
public void removeEnemy(Sprite sprite){
        enemies.remove(sprite);
        Pools.free(sprite);
    }



//this is the error there I get:

Exception in thread "LWJGL Application" java.util.ConcurrentModificationException
   at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
   at java.util.ArrayList$Itr.next(ArrayList.java:851)
   at com.dreamroad.savethetree.EnemyClass.update(EnemyClass.java:66)
   at com.dreamroad.savethetree.MyGdxGame.render(MyGdxGame.java:51)
   at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:215)
   at com.badlogic.gdx.backends.lwjgl.LwjglApplication.run(LwjglApplication.java:120)

Process finished with exit code 0

我认为这是我收到错误的原因，但我不确定：

public void draw(SpriteBatch batch){
        for(Sprite drawEnemy:enemies) {    //enemies is the ArrayList
            drawEnemy.draw(batch);
            drawEnemy.translateY(deltaTime * movement);
        }
    }

Answer 1

问题是你正在尝试删除当前正在迭代的列表中的某些内容，在这种情况下我总是做的事情是创建一个额外的列表，其中包含应该删除的 Sprites，然后在遍历列表后删除它们（或者，在更新方法的末尾，或类似的方法）

一个说明我的想法的简短代码示例：

//removing the enemy
//Initialize a list to store the sprites to be removed
List<Sprite> toBeRemovedSprites = new ArrayList<Sprite>();
while (enemyIterator.hasNext()){
    Sprite nextEnemy=enemyIterator.next(); //I get the error here..<--
    if(enemySpr.getY()+enemySpr.getHeight()>=treeObj.treeSpr.getY()){
        removeEnemy(nextEnemy);
        toBeRemovedSprites.add(nextEnemy);
    }
}
//Remove the sprites that should be deleted, after iterating over the list
for(Sprite s : toBeRemovedSprites){
    enemies.remove(s);
}



//removeEnemy method
public void removeEnemy(Sprite sprite){
    //Remove this line that removes the sprite from the list
    //enemies.remove(sprite);
    Pools.free(sprite);
}

你可以做的另一件事就是使用迭代器的 remove 函数，想象它看起来像这样：

//removing the enemy
while (enemyIterator.hasNext()){
    Sprite nextEnemy=enemyIterator.next(); //I get the error here..<--
    if(enemySpr.getY()+enemySpr.getHeight()>=treeObj.treeSpr.getY()){
        removeEnemy(nextEnemy, enemyIterator);
    }
}



//removeEnemy method
public void removeEnemy(Sprite sprite, Iterator<Sprite> enemyIterator){
    //Change the line to remove using the iterator
    //enemies.remove(sprite);
    enemyIterator.remove();
    Pools.free(sprite);
}

Answer 2

正如 Subler 所说，这里的问题是您试图在遍历列表的同时从列表中删除某些内容。

但是，有一个更简单的解决方案。只需在迭代器上调用 remove() 即可。这将删除迭代器的当前元素。

//removing the enemy
while (enemyIterator.hasNext()) {

    Sprite nextEnemy = enemyIterator.next();
    if(enemySpr.getY() + enemySpr.getHeight() >= treeObj.treeSpr.getY()) {
        enemyIterator.remove();
        Pools.free(nextEnemy);
    }
}

当 Sprites 到达特定位置时，我该如何移除它们？

How do I remove Sprites when they go on a specific position?

java

position

sprite

libgdx