从ArrayList中删除元素

Question

I have a Singleton class called User , this user have an ArrayList. now i have a ListView that display User's elements , selecting them and next press a button it will delete selected ones; in this case :

    view.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE_MODAL);
    view.setMultiChoiceModeListener(new AbsListView.MultiChoiceModeListener() {

        ArrayList<Chat> elementsToErase= new ArrayList<Chat>();
        @Override
        public void onItemCheckedStateChanged(ActionMode actionMode, int i, long l, boolean b) {



            if(b) {
                elementsToErase.add((Chat)view.getItemAtPosition(i));


            }
                else{
                    elementsToErase.remove((Chat)view.getItemAtPosition(i));

            }




        }

        @Override
        public boolean onCreateActionMode(ActionMode actionMode, Menu menu) {
            MenuInflater inflater = actionMode.getMenuInflater();
            inflater.inflate(R.menu.menu_chat_edit, menu);
            view.setSelected(true);
            return true;
        }

        @Override
        public boolean onPrepareActionMode(ActionMode actionMode, Menu menu) {
            return false;
        }

        @Override
        public boolean onActionItemClicked(ActionMode actionMode, MenuItem menuItem) {
            switch (menuItem.getItemId()) {
            case R.id.delete_chat:
               Arraylist<Chat> userElement =          User.getIstance().getChats();
                for (int i = 0; i < elementsToRemove.size(); ++i) {
                userElement.removeChat(elementsToRemove.get(i));



                }

                adapter.notifyDataSetChanged();
                actionMode.finish();
                return true;

            default:
                return false;
            }

        }

before delete, if i create a new chat and try to add some text in it works. After delete, if i create a new chat and try to add some text it won't add the text.

this is how i remove elements from ArrayList :

   for(int i = 0 ; i < chats.size();++i){
          if(chats.get(i).equals(chat)) {
              return  chats.remove(i);
       }
        }
    return new Chat("null",0);
}

It's possible that i "break" the reference to the User ArrayList?

Answer 1

If you use this:

Arraylist<Chat> userElement = User.getIstance().getChats();

Both userElement and User.getIstance().getChats() will use the same underlining array , modification done to either one of them will reflect in the other one.

If you want to have two different Objects , create the second ArrayList like this:

Arraylist<Chat> userElement = new ArrayList <Char>(User.getIstance().getChats());

Also, this loop:

   for(int i = 0 ; i < chats.size();++i){
      if(chats.get(i).equals(chat)) {
          return  chats.remove(i);
       }
    }

will throw a ConcurrentModificationException , if you want to remove Object s from a List while you iterate it, you have to use an Iterator .