How to delete multiple selected line items from a listview?

Question

I have implemented a simple method to delete multiple items from a listview following this solution Removing muliple items from listview using Check box in Android, then modified it a small bit to allow for a switch statement for the two button click events, add & delete.But the problem is when I click the delete button the app crashes giving me these errors: http://pastebin.com/2NmCQk2B

I'm not sure why I'm getting the null pointer exception as I believe I have assigned everything correctly.

Can someone better explain why I could be getting this error? Or perhaps a better way of deleting selected line items from a listview?

The complete class is posted below for better understanding:

public class TopRatedFragment extends Fragment implements OnClickListener {

    ListView mListView;
    EditText mValue;
    Button mAdd,mDel;
    ArrayList<String> list = new ArrayList<String>();
    ArrayAdapter<String> adapter;
    SparseBooleanArray mCheckStates ;


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_top_rated, container, false);
         mAdd = (Button)rootView.findViewById(R.id.newList);
         mDel = (Button)rootView.findViewById(R.id.delBtn);
         mAdd.setOnClickListener(this);
         mDel.setOnClickListener(this);
         mValue = (EditText)rootView.findViewById(R.id.listData);
         adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_expandable_list_item_1, list);

    // set the lv variable to your list in the xml
         mListView=(ListView)rootView.findViewById(R.id.listView);  
         mListView.setAdapter(adapter);


        return rootView;    
    }


    public void onClick(View v)
    {
        switch(v.getId()){
        case R.id.newList:
             //DO something
            String input = mValue.getText().toString();
            if(input.length() > 0)
            {
                // add string to the adapter, not the listview
                adapter.add(input);
                // no need to call adapter.notifyDataSetChanged(); as it is done by the adapter.add() method
            }
        break;
        case R.id.delBtn:
             //DO something
            SparseBooleanArray checked = mListView.getCheckedItemPositions();
            for (int i = 0; i < mListView.getCount(); i++){

                //line 65
                if (checked.get(i)==true)
                {
                     list.remove(i);

                } 
                adapter.notifyDataSetChanged(); 

            }
             mListView.clearChoices();               
        }


    }   

}

Listview/Interface

I populate list by entering items in edittext and clicking add button — Brian Var, Jan 13 '14 at 19:39
First thing is to see is that your "checked" variable is null. Figure out why it´s null and then you´ll have something going. If you can´t figure out why "getCheckItemPositions" returns null, have a read here http://stackoverflow.com/questions/7402150/getcheckeditempositions-always-returning-null-android-listview , also, be absolutely sure to NOT HAVE choice mode in ListView set to CHOICE_MODE_NONE. — Chayemor, Jan 13 '14 at 19:48
I just noticed that this listview does not include check boxes so this is probably why it is crashing because null pointer.How can I make the listview include checkboxes? — Brian Var, Jan 13 '14 at 19:53
I have added a screen shot of the interface,you see there is no check boxes,how do I make the listview with checkboxes? — Brian Var, Jan 13 '14 at 19:57
@BrianJ `listview.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);` — Raghunandan, Jan 13 '14 at 19:57
@Raghunandan so it would just be mListView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE); and then the listview will includes `checks`? — Brian Var, Jan 13 '14 at 20:13
@Raghunandan is there a simple way to have the text item be striked through when the checkbox is ticked? — Brian Var, Jan 13 '14 at 20:59

vipul mittal · Answer 1 · 2014-01-13T19:47:54.603

1

Remove from adapter instead from listview try following:

 SparseBooleanArray checked = mListView.getCheckedItemPositions();

  if(checked!=null){
  for (int i = 0; i < mListView.getCount(); i++){

            //line 65
            if (checked.get(i)==true)
            {
                 adapter.remove(mListView.getItemAtPosition(i));

            } 
            adapter.notifyDataSetChanged(); 

        }
         mListView.clearChoices(); 
   }

getCheckedItemPositions Returns: A SparseBooleanArray which will return true for each call to get(int position) where position is a checked position in the list and false otherwise, or null if the choice mode is set to CHOICE_MODE_NONE.

edited Jan 13 '14 at 19:47

answered Jan 13 '14 at 19:42

vipul mittal

17,343
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why would `if (checked.get(i)==true)` line 65 throw NPE?? – Raghunandan Jan 13 '14 at 19:44
check for null before for loop – vipul mittal Jan 13 '14 at 19:45
Reverse the for loop: start at the end. – greenapps Jan 13 '14 at 22:03

score 1 · Accepted Answer · answered Jan 13 '14 at 19:43

You need to use valueAt(), the working code should be

SparseBooleanArray checkedItems = mListView.getCheckedItemPositions();
if (checkedItems != null) {
    for (int i=0; i<checkedItems.size(); i++) {
        if (checkedItems.valueAt(i)) {
            String item = mListView.getAdapter().getItem(
                                  checkedItems.keyAt(i)).toString();
            Log.i(TAG,item + " was selected");
        }
    }
}

score 0 · Answer 3 · answered Jun 26 '14 at 04:31

I used loop this way, and it worked:

SparseBooleanArray checkedItemPositions = getListView().getCheckedItemPositions();
                int itemCount = getListView().getCount();

                for(int i=itemCount-1; i >= 0; i--){
                    if(checkedItemPositions.get(i)){
                        adapter.remove(list.get(i));
                    }
                }
                checkedItemPositions.clear();
                adapter.notifyDataSetChanged();

How to delete multiple selected line items from a listview?

3 Answers3