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copied!<p>Ok with the help of Mr JohnEye, I've been able to fix the problem in my code. Consider the following snippet:</p> <pre><code> protected void checkSoldierCollision() { // TODO Auto-generated method stub int numBombs = bombGroup.getChildCount(); int numTroops = troopsGroup.getChildCount(); final ArrayList<Sprite> toBeDetached = new ArrayList<Sprite>(); for (int i = 0; i < numBombs; i++) { Sprite s = (Sprite) bombGroup.getChildByIndex(i); for (int j = 0; j < numTroops; j++) { Sprite s2 = (Sprite) troopsGroup.getChildByIndex(j); if (s.collidesWith(s2)) { Sprite splat = createSplat(); splat.setPosition(s.getX(), s.getY()); getEngine().getScene().attachChild(splat); Sprite splode = createExplosion(); splode.setPosition(s.getX(), s.getY()); explodeGroup.attachChild(splode); // getEngine().getScene().attachChild(splode); // WARNING: cannot detach from the list // while looping through the list toBeDetached.add(s); toBeDetached.add(s2); } } } runOnUpdateThread(new Runnable() { @Override public void run() { for (Sprite s : toBeDetached) { s.detachSelf(); Sprite splat = createSplat(); splat.setPosition(s.getX(), s.getY()); getEngine().getScene().attachChild(splat); Sprite splode = createExplosion(); splode.setPosition(s.getX(), s.getY()); explodeGroup.attachChild(splode); // getEngine().getScene().attachChild(splode); } toBeDetached.clear(); } }); } </code></pre> <p>As I've mentioned, the game crashes because of a discrepancy in count between the 2 colliding objects. This situation happens when, as Mr. JohnEye points out, a sprite is spawned in the UI thread, but not in the Update thread as well. Furthermore, consider my createExplosion, createBomb and createSplat functions:</p> <p>CREATE BOMB</p> <pre><code> public Sprite createBomb(float x, float y) { Sprite bombSprite = new Sprite(x, y, this.mBombTextureRegion, getVertexBufferObjectManager()); MoveYModifier downModBomb = new MoveYModifier(1, 60, FLOOR); downModBomb.addModifierListener(new IModifierListener<IEntity>() { @Override public void onModifierStarted(IModifier<IEntity> pModifier, IEntity pItem) { } @Override public void onModifierFinished(IModifier<IEntity> pModifier, final IEntity pItem) { runOnUpdateThread(new Runnable() { @Override public void run() { pItem.detachSelf(); } }); AnimatedSprite explodeSprite = createExplosion(); explodeSprite.setPosition(pItem.getX(), FLOOR); explodeGroup.attachChild(explodeSprite); // getEngine().getScene().attachChild(explodeGroup); } }); bombSprite.registerEntityModifier(downModBomb); return bombSprite; } </code></pre> <p>CREATE EXPLOSION</p> <pre><code>public AnimatedSprite createExplosion() { AnimatedSprite boomSprite = new AnimatedSprite(0, 0, this.mExplodeTextureRegion, getVertexBufferObjectManager()); DelayModifier delay = new DelayModifier(.3f); // delay in seconds, can // take float numbers .5 // seconds delay.addModifierListener(new IModifierListener<IEntity>() { @Override public void onModifierStarted(IModifier<IEntity> pModifier, IEntity pItem) { ((AnimatedSprite) pItem).animate(new long[] { 100, 100, 100 }, // durations/frame new int[] { 1, 2, 3 }, // which frames true); // loop } @Override public void onModifierFinished(IModifier<IEntity> pModifier, final IEntity pItem) { runOnUpdateThread(new Runnable() { @Override public void run() { ((AnimatedSprite) pItem).detachSelf(); } }); } }); boomSprite.registerEntityModifier(delay); // register action return boomSprite; } </code></pre> <p>CREATE SPLAT</p> <pre><code>public Sprite createSplat() { Sprite splatSprite = new Sprite(0, 0, this.mSplatTextureRegion, getVertexBufferObjectManager()); DelayModifier delay = new DelayModifier(.3f); // delay in seconds, can // take float numbers .5 // seconds delay.addModifierListener(new IModifierListener<IEntity>() { @Override public void onModifierStarted(IModifier<IEntity> pModifier, IEntity pItem) { } @Override public void onModifierFinished(IModifier<IEntity> pModifier, final IEntity pItem) { runOnUpdateThread(new Runnable() { @Override public void run() { pItem.detachSelf(); } }); } }); splatSprite.registerEntityModifier(delay); // register action return splatSprite; } </code></pre> <p>Notice that all of them detach/generate other sprites in the runOnUpdate thread. The game crashes in my earlier run-throughs because I did not detach/generate all these sprites on the runOnUpdate class. </p>

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