列表视图使用ArrayList null指针填充

Question

我正试图使用我在这里找到的教程从数组列表中创建一个列表视图。行可以是球队名称，也可以是球员名称。现在，当我向下滚动时，它工作得很好，但当我向上滚动时，会给出一个null指针，通常是因为与名称相关的行试图设置团队名称textview，反之亦然（我从日志语句中确定了这一点）。例如，isPlayerName设置为true的视图在我设置viewholder.player_name的行上给出了一个null指针。我认为这与getTag（）方法没有引用正确的对象有关。当我只使用播放器行时，教程运行得很好（可能是因为所有的viewholder对象都已实例化）。这是我的列表适配器：私有类CustomAdapter扩展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;
    }
}

这是我的viewHolder，我对两种类型的行都使用相同的字段，但只有某些字段会被实例化，这取决于它是团队还是球员行

    private class ViewHolder {
    ImageView team_icon;
    TextView player_name;
    RelativeLayout layout;
    TextView team_name;
}

是因为我不理解getTag（）方法吗？

Answer 1

Kevin，

根据您的代码，您似乎正确地理解了getTag()和setTag()。以防万一，让我为你分解一下：

"标记"是指附加到另一个对象上的对象（任何对象）。它没有特定类型的配对，但通常用于将数据对象（如viewHolder）与非数据对象（例如View）配对。不幸的是，这意味着如果使用"标记"，您必须自己进行类型检查。

"标记"最常见的问题是，许多开发人员获取了错误视图的"标记"，从而获得了错误甚至为空的数据。您的代码似乎并非如此。但是，您有所有的Log.d()语句。如果我们有一份日志，我们肯定能更容易地帮助你眨眼轻推轻推

希望这能有所帮助，

FuzzicalLogic