Concurrent Modification Exception : adding to an ArrayList

Question

The problem occurs at

Element element = it.next();

And this code which contains that line, is inside of an OnTouchEvent

Answer 1

adding from list in this case leads to CME, no amount of synchronized will let you avoid that. Instead, consider adding using the iterator...

        for(ListIterator it = mElements.listIterator(); it.hasNext();){
            Element element = it.next();

            if(touchX > element.mX  && touchX < element.mX + element.mBitmap.getWidth() && touchY > element.mY   
                    && touchY < element.mY + element.mBitmap.getHeight()) {  

                //irrelevant stuff..

                if(element.cFlag){
                    // mElements.add(new Element("crack",getResources(), (int)touchX,(int)touchY));
                    it.add(new Element("crack",getResources(), (int)touchX,(int)touchY));
                    element.cFlag = false;

                }           
            }
        }

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Also I think it's somewhat slippery to state like...

...The problem occurs at Element element = it.next();

for the sake of precision note that above is not guaranteed.

API documentation points out that this ...behavior cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast operations throw ConcurrentModificationException on a best-effort basis...