I m trying to make a listview from an arraylist using the tutorial i found here. The rows can either be a team name or a player name. Right now it works fine when I scroll down, but gives a nullpointer when I scroll back up, usually because a row that is associated with a name is trying to set the team name textview or vice versa (i determined this from my log statements). Ex. a view with isPlayerName set to true gives a nullpointer on the line where I set viewholder.player_name. I think it has something to do with the getTag() method not referencing the right object. The tutorial worked fine when I used only player rows, (probably because all of viewholders objects were instaiated). Here is my listadapter: private class CustomAdapter extends BaseAdapter {

    private ArrayList<ArrayList<String>> player_array;
    private LayoutInflater inflater;

    public CustomAdapter(Context context, ArrayList<ArrayList<String>> array){
        player_array = array;
        inflater = LayoutInflater.from(context);
    }

    @Override
    public int getCount() {
        return player_array.size();
    }

    @Override
    public Object getItem(int position) {
        return player_array.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewholder= new ViewHolder();
        boolean isPlayerName = (player_array.get(position).size() > 1 ? true : false);
        if (convertView == null){
        if (isPlayerName){
            convertView = inflater.inflate(R.layout.player_list_item, null);
            viewholder.player_name = (TextView)convertView.findViewById(R.id.player_name);
            viewholder.layout = (RelativeLayout)convertView.findViewById(R.id.player_list_item_layout);
        }
        else {
            convertView = inflater.inflate(R.layout.team_item, null);
            viewholder.team_icon = (ImageView)convertView.findViewById(R.id.team_logo);
            viewholder.team_name = (TextView)convertView.findViewById(R.id.team_name);
        }
        convertView.setTag(viewholder);
        }
        else {
            viewholder = (ViewHolder)convertView.getTag();
        }
        if (isPlayerName){
            try {
                viewholder.player_name.setText((player_array.get(position)).get(0));
                viewholder.layout.setOnClickListener(new CustomOnClickListener(player_array.get(position).get(1)));
            }
            catch (NullPointerException e){
                Log.d("NULL", "is viewholder null? " + (viewholder == null));
                Log.d("NULL", "is player name? " + isPlayerName);
                Log.d("NULL", "is getTag null? " + (convertView.getTag() == null));
                Log.d("NULL", "is team name null " + (viewholder.team_name == null));
                Log.d("NULL", "is team icon null " + (viewholder.team_icon == null));
                Log.d("NULL", "is player name null " + (viewholder.player_name == null));
                Log.d("NULL", "is link null? " + (player_array.get(position).get(1) == null));
                Log.d("NULL", "is layout null? " + (viewholder.layout == null));
            }

        }
        else {
            String team_name = player_array.get(position).get(0);
            try {
            viewholder.team_name.setText(Character.toUpperCase(team_name.charAt(0)) + team_name.substring(1));
            }
            catch (NullPointerException e){
                Log.d("NULL", "is player name? " + isPlayerName);
                Log.d("NULL", "is getTag null? " + (convertView.getTag() == null));
                Log.d("NULL", "is team name null " + (viewholder.team_name == null));
                Log.d("NULL", "is team icon null " + (viewholder.team_icon == null));
                Log.d("NULL", "is player name null " + (viewholder.player_name == null));
            }
            if (team_name.equals("hawks")){
                viewholder.team_icon.setBackgroundResource(R.drawable.hawks);
            }
            else if (team_name.equals("lions")){
                viewholder.team_icon.setBackgroundResource(R.drawable.lions);
            }
            else if (team_name.equals("sparks")){
                viewholder.team_icon.setBackgroundResource(R.drawable.sparks);
            }
            else if (team_name.equals("bulls")){
                viewholder.team_icon.setBackgroundResource(R.drawable.bulls);
            }
            else if (team_name.equals("renegades")){
                viewholder.team_icon.setBackgroundResource(R.drawable.renegades);
            }
            else if (team_name.equals("poppiezz")){
                viewholder.team_icon.setBackgroundResource(R.drawable.poppiezz);
            }
            else if (team_name.equals("mambas")){
                viewholder.team_icon.setBackgroundResource(R.drawable.mambas);
            }
            else if (team_name.equals("78sixers")){
                viewholder.team_icon.setBackgroundResource(R.drawable.sixers);
            }
            else if (team_name.equals("brooklynites")){
                viewholder.team_icon.setBackgroundResource(R.drawable.brooklynites);
            }
            else if (team_name.equals("blazers")){
                viewholder.team_icon.setBackgroundResource(R.drawable.blazers);
            }
            else if (team_name.equals("warriors")){
                viewholder.team_icon.setBackgroundResource(R.drawable.warriors);
            }
            else {
                viewholder.team_icon.setBackgroundResource(R.drawable.basketball);
            }
        }
        return convertView;
    }

}

And here is my viewHolder, I use the same one for both types of rows, but only certain fields get instantiated depending on if it is a team or a player row

    private class ViewHolder {

    ImageView team_icon;
    TextView player_name;
    RelativeLayout layout;
    TextView team_name;
}

之所以如此,是因为我不理解“骗局”方法?