Concurrent Modification when requesting list size

问题

I'm trying to get a List it's size but when doing this I'm getting a ConcurrentModificationException on the size() method. This is weird because I'm not trying to modify the list while iterating over it. Here's some of my code that might have caused it but I can't see the problem with it.

The main method:

private void setupCharacterGrid() {

    currentCharacters.add(0, new Character("add", "add"));
    if (currentCharacters.size() < 9) {
        sub(0, currentCharacters.size(), currentCharacters.size());
    } else {
        sub(0, 9, 9);
    }

    fillGrids();

    charPager.setAdapter(new CustomPagerAdapter(characterGrids));
    charPager.setCurrentItem(0);

}

The sub method (the method where the list is filled) please note that the dividedCharList is of the type: List> where Character is a custom POJO.

private void sub(int start, int end, int n) {
    int size = currentCharacters.size();
    if (start > size) {
        return;
    } else if (start == size) {
        // new list(currentcharacters.get(start))
        // check if it fits on the previous grid
        List<Character> lastGrid = dividedCharList.get(dividedCharList
                .size() - 1);
        if (lastGrid.size() < 9) {
            lastGrid.add(currentCharacters.get(start - 1));
        } else {
            List<Character> finalCharList = new ArrayList<Character>();
            finalCharList.add(currentCharacters.get(start - 1));
            dividedCharList.add(finalCharList);
        }
        return;
    } else {
        if (size < start + n) {
            sub(start, end, n--);
        } else {
            // new list(currentcharacters.sublist(start, end);
            // end = end + n;
            // start = end + 1
            dividedCharList.add(currentCharacters.subList(start, end));
            start = end + 1;
            end = end + n;
            sub(start, end, n);
        }
    }
}

The method where the exception occurs when trying to get the size:

private synchronized void fillGrids() {
    for (int i = 0; i < dividedCharList.size(); i++) {
        GridView gridView = new GridView(this);
        gridView.setNumColumns(3);
        CharacterGridAdapter aa = new CharacterGridAdapter(this,
                R.layout.charactergrid_cell, dividedCharList.get(i));
        gridView.setAdapter(aa);
        characterGrids.add(gridView);
    }
}

Please note that the exception also occurs when I'm trying to iterate trough the List and try to get a value and display it in a log

Edit

I've just noticed the exception occurs while calling gridView.setAdapter(), the getCount method of the ArrayAdapter throws the ConcurrentModificationException

Edit2

Here's the stacktrace, it might help:

01-24 13:03:44.942: E/AndroidRuntime(15336): FATAL EXCEPTION: main
01-24 13:03:44.942: E/AndroidRuntime(15336): java.util.ConcurrentModificationException
01-24 13:03:44.942: E/AndroidRuntime(15336): at                 java.util.AbstractList$SubAbstractList.size(AbstractList.java:360)
 01-24 13:03:44.942: E/AndroidRuntime(15336):   at    android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
 01-24 13:03:44.942: E/AndroidRuntime(15336):   at android.widget.GridView.setAdapter(GridView.java:182)
 01-24 13:03:44.942: E/AndroidRuntime(15336):   at xx.ProfileActivity.fillGrids(ProfileActivity.java:111)
 01-24 13:03:44.942: E/AndroidRuntime(15336): 
 xx.ProfileActivity.setupCharacterGrid(ProfileActivity.java:96)
 01-24 13:03:44.942: E/AndroidRuntime(15336):   at xx.ProfileActivity.access$6(ProfileActivity.java:87)

On request the Adapter code

public class CharacterGridAdapter extends ArrayAdapter<Character> {

private Context context;
private List<Character> objects;
private int resource;

public CharacterGridAdapter(Context context, int resource, List<Character> listChar) {
    super(context, resource);
    this.context = context;
    this.objects = listChar;
    this.resource = resource;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View rowView = convertView;
    if (rowView == null) {
        LayoutInflater inflater = ((Activity) context).getLayoutInflater();
        rowView = inflater.inflate(R.layout.charactergrid_cell, null);
    } else {
    }
    return rowView;
}

}

Anyone who could help me with this one?

回答1:

Remove 'synchronized' and instead of using List use CopyOnWriteArrayList. You can find more information here CopyOnWriteArrayList

来源：https://stackoverflow.com/questions/21332054/concurrent-modification-when-requesting-list-size

标签

java

android

concurrentmodification