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これは、自分で修正できないコードです。

カスタム ArrayAdapter を作成して、ListView にプレイヤーの名前を含む TextView を設定しました。

アダプターがインスタンス化される前にプレーヤー名のリスト全体が指定されている場合、意図したとおりに機能します。この問題は、アダプタのインスタンス化後に追加されたリスト項目をクリックすると発生します。

NullPointerException が発生する理由がわかりません:

PlayersArrayAdapter.getItemId(int position)

この行で：

return mIdMap.get(item);

リストで「フライドポテト」という名前の3番目のプレーヤーをクリックすると。

説明付きのコード:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_match_settings);

    //arraylist to store players names
    ArrayList<String> playerNames = new ArrayList<String>();

    //players which are on the list from the begining
    //when I click on them, "onPlayerListItemClicked" is properly called
    //and I get clicked player name in my LogCat
    playerNames.add("Pawel");
    playerNames.add("Olga");

    //listview to display players names
    ListView playerListView = (ListView)findViewById(R.id.ms_player_list);

    //custom arrayadapter, which gets ArrayList as one of arguements
    PlayersArrayAdapter playerListAdapter = new PlayersArrayAdapter(this, R.layout.player_list_item, playerNames);  

    playerListView.setAdapter(playerListAdapter);
    playerListView.setOnItemClickListener(onPlayerListItemClicked);


    // THERE IS ROOT OF PROBLEM:
    // player "Fries" is also added to the ListView, and is properly displayed
    // but when I click on it, I get NullPointerException described above
    playerNames.add("Fries");
    playerListAdapter.notifyDataSetChanged();
}

OnItemClickListener onPlayerListItemClicked = new OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, final View view, int position, long id) {
        String item = (String)parent.getItemAtPosition(position);
        Logger.i("Clicked at item: " + item);
    }
};

PlayersArrayAdapter クラス:

class PlayersArrayAdapter extends ArrayAdapter<String>{

    HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();

    public PlayersArrayAdapter(Context context, int textViewResourceId, List<String> objects) {
        super(context, textViewResourceId, objects);

        for (int i = 0; i < objects.size(); i++)
            mIdMap.put(objects.get(i), i);
    }

    @Override
    public long getItemId(int position) {
        String item = getItem(position);
        return mIdMap.get(item); //at this line NullPointerException throws
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

}

デバッグからのエラー メッセージ:

Thread [<1> main] (Suspended (exception NullPointerException))  
    <VM does not provide monitor information>   
    PlayersArrayAdapter.getItemId(int) line: 119    
    AbsListView$PerformClick.run() line: 1964   
    ViewRoot(Handler).handleCallback(Message) line: 587 
    ViewRoot(Handler).dispatchMessage(Message) line: 92 
    Looper.loop() line: 130 
    ActivityThread.main(String[]) line: 3687    
    Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]  
    Method.invoke(Object, Object...) line: 507  
    ZygoteInit$MethodAndArgsCaller.run() line: 867  
    ZygoteInit.main(String[]) line: 625 
    NativeStart.main(String[]) line: not available [native
4

1 に答える 1

1 
@Override
public long getItemId(int position) {
    return position // this needs to just return a long, position usually is best choice
}
于 2013-09-09T21:15:53.577 に答える