Question

我正在使用BaseAdapter创建列表视图，我想按下添加按钮时动态添加列表项。但是现在我得到了这个空指针异常。

07-02 06:40:41.650: E/AndroidRuntime(1940): FATAL EXCEPTION: main
07-02 06:40:41.650: E/AndroidRuntime(1940): java.lang.NullPointerException
07-02 06:40:41.650: E/AndroidRuntime(1940):     at com.ui.activities.AddHorseCompetitionResult$1.onClick(AddHorseCompetitionResult.java:61)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at android.view.View.performClick(View.java:4204)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at android.view.View$PerformClick.run(View.java:17355)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at android.os.Handler.handleCallback(Handler.java:725)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at android.os.Handler.dispatchMessage(Handler.java:92)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at android.os.Looper.loop(Looper.java:137)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at android.app.ActivityThread.main(ActivityThread.java:5041)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at java.lang.reflect.Method.invokeNative(Native Method)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at java.lang.reflect.Method.invoke(Method.java:511)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-02 06:40:41.650: E/AndroidRuntime(1940):     at dalvik.system.NativeStart.main(Native Method)

这是我的java类

public class AddCompetitionResult extends Fragment {

    private CompetitionResultListAdapter competitionResultListAdapter;
    private DataManager datamanager;
    ArrayList<Result> result;
    ListView listView;
    private Horse horse;
    private Button addResults;
    int clickCounter=0;
    int resultId = 1;

    public AddHorseCompetitionResult(Horse horse) {
        this.horse = horse;
    }

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.add_horse_competition_result,
                null);

        addResults = (Button) view.findViewById(R.id.btn_add_competition_result);

        listView = (ListView) view.findViewById(R.id.data_list);
        // result = datamanager.create(getActivity());

        competitionResultListAdapter = new CompetitionResultListAdapter(result, getActivity());

        View footerView = ((LayoutInflater) getActivity().getSystemService(
                Context.LAYOUT_INFLATER_SERVICE)).inflate(
                R.layout.competition_result_listview_footer, null, false);

        listView.addFooterView(footerView);

        listView.setAdapter(competitionResultListAdapter);

        addResults.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                result.add(new Result("resultId"));
                competitionResultListAdapter.notifyDataSetChanged();
                resultId++;

            }
        });

        listView.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                    int position, long id) {
                if (competitionResultListAdapter.getCount() == position) {
                    MainActivity mainActivity = MainActivity.getInstance();
                    mainActivity.setFragment(new AddHorseDetailedInfo(horse),
                            "Add horse more info");
                    // datamanager.createResult(result);

                } else {
                    // ContactGroup cg = (ContactGroup)
                    // competitionResultListAdapter.getItem(position);
                    // MainActivity mainActivity = MainActivity.getInstance();
                    // mainActivity.setFragment(new
                    // ContactListView(cg.getGroupId()), "contacts");
                }
            }

        });

        return view;

    }
}

适配器

public class CompetitionResultListAdapter extends BaseAdapter{

    private Activity activity;
    private ArrayList<Result> result;
    DataManager datamanager;

    public CompetitionResultListAdapter( ArrayList<Result> result, Activity activity){
        this.result = result;
        this.activity = activity;
    }

    @Override
    public int getCount() {
        return result!=null ? result.size() : 0;
    }

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(convertView==null){
            // inflate the layout
            LayoutInflater inflater = activity.getLayoutInflater();
            convertView = inflater.inflate(R.layout.list_item_competition_result, parent, false);
        }
        EditText listItemDate = (EditText) convertView.findViewById(R.id.date);
        EditText listItemPlace = (EditText) convertView.findViewById(R.id.place);
        EditText listItemComment = (EditText) convertView.findViewById(R.id.comment);
        result.get(position).setDate(listItemDate.getText().toString());
        result.get(position).setPlace(listItemPlace.getText().toString());
        result.get(position).setComment(listItemComment.getText().toString());


        return convertView;
    }

    public void refreshResultList(ArrayList<Result> result){
        this.result = result;
        notifyDataSetChanged();

    }

}

Answer 1

您的result ArrayList未初始化。所以在构造函数中初始化它 -

public class AddCompetitionResult extends Fragment {

    private CompetitionResultListAdapter competitionResultListAdapter;
    private DataManager datamanager;
    ArrayList<Result> result;
    ListView listView;
    private Horse horse;
    private Button addResults;
    int clickCounter=0;
    int resultId = 1;

    public AddHorseCompetitionResult(ArrayList<Result> result, 
     Horse horse) {
        this.horse = horse;
       /*Initialize here if you 
       passed the value somewhere (1)*/
        this.result = result; 
    }

    public View onCreateView(LayoutInflater inflater, 
    ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.
        add_horse_competition_result, null);

        /*Haven't passed the value to constructor*/
        /*anywhere then do this (2)*/
        result = new ArrayList<Result>();
        result.add(new Result("resultId")); 
        return view;

    }
}

注意：

（1）初始化的方式是将此值从其他地方传递给此构造函数。

（2）否则你可以按照方式进行2-

ArrayList<Result> result = new ArrayList<Result>();

Answer 2

看起来result永远不会被初始化bevor the line：

result.add(new Result("resultId"));

被召唤。

Answer 3

在使用之前初始化arraylist。

ArrayList<Result> result  = new ArrayList<Result>();

在动态添加listitem时获取NullPointerException

3 个答案: