下面的代码我不能修复。
我创建了一个自定义的 ArrayAdapter,使用 TextViews 来填充 ListView 列表,包含 player 的名字。
当 player names 的整个列表都在实例 adapter 前指定,就能按预期的运行。
在实例化 adapter后,当我点击一个 list item 添加时,问题就出现了。
当我点击列表中第三个名是"Fries"的 player 时,我不清楚为什么在return mIdMap.get(item);
行的PlayersArrayAdapter.getItemId(int position)
里面获得一个NullPointerException
异常。
代码:
@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 class:
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;
}
}
Debug 的错误信息:
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