在Android可扩展列表视图中获取空指针异常

Question

我是 Android应用程序开发的初学者。我对Java`集合没有很好的了解。我必须在可扩展列表中显示数据。我们正在使用 OData服务从后端获取数据。

我已按照http://www.androidhive.info/2013/07/android-expandable-list-view-tutorial/在可展开列表中显示我的数据。我能够显示标题数据。但是，当我在可扩展列表视图中单击Header项时，我的Adapter TeamDetailsAdapter中的getChildrenCount()处的空指针异常。

我的活动如下。我没有提到整个代码。我在下面提到了fetchData()方法。

private ArrayList<Level1> listDataHeader = new ArrayList<Level1>();
private HashMap<String, ArrayList<Level2>> listDataChild = new HashMap<String, ArrayList<Level2>>();
private ArrayList<Level2> emps = new ArrayList<Level2>();

fetchData();

expListView = (ExpandableListView) findViewById(R.id.lvTeamDetailsExpList);

expListAdapter = new TeamDetailsAdapter(this, listDataHeader, listDataChild);

expListView.setAdapter(expListAdapter);


fetchdata()
{
.................
................
                for(int i =0; i<n; i++)
                {
                    ISDMODataEntry entry = entries.get(i);



                    if(entry.getPropertyValue("Olevel").equals("1"))
                    {
                        Level1 _level1 = new Level1();
                        _level1.setEmpId(entry.getPropertyValue("EmpNo"));
                        _level1.setEmpName(entry.getPropertyValue("EmpName"));
                        listDataHeader.add(_level1);  
                    }   


                }   

                for(int j = 0; j<listDataHeader.size(); j++)
                {

                    for(int k =0; k<n; k++)
                    {
                        ISDMODataEntry entry2 = entries.get(k);

                        Level2 _level2 = new Level2();

                        if(entry2.getPropertyValue("ManagerName").equals(listDataHeader.get(j).getEmpName()))   
                        {
                            System.out.println("MngrName: " + entry2.getPropertyValue("ManagerName") + "Row name: " + listDataHeader.get(j).getEmpName());
                            _level2.setEmpId(entry2.getPropertyValue("EmpNo"));
                            _level2.setEmpName(entry2.getPropertyValue("EmpName"));
                            emps.add(_level2);      
                            listDataChild.put(listDataHeader.get(j).getEmpName().toString(), emps);
                        }

                    }
                    System.out.println("Emp Size: " + emps.size());

                }

}

---

以下是我的适配器类

public class TeamDetailsAdapter extends BaseExpandableListAdapter{

    private Context _context;   
    private ArrayList<Level1> _listDataHeader;
    private HashMap<String, ArrayList<Level2>> _listDataChild;



    public TeamDetailsAdapter(Context context,
            ArrayList<Level1> listDataHeader,
            HashMap<String, ArrayList<Level2>> listDataChild) {
        // TODO Auto-generated constructor stub
        this._context = context;
        this._listDataHeader = listDataHeader;
        this._listDataChild = listDataChild;
    }

    @Override
    public Object getChild(int groupPosition, int childPosititon) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition))
                .get(childPosititon);
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public View getChildView(int groupPosition, final int childPosition,
            boolean isLastChild, View convertView, ViewGroup parent) {
        //final String childText = (String) getChild(groupPosition, childPosition);
        final Level2 childText = (Level2) getChild(groupPosition, childPosition);
        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this._context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(
                    R.layout.team_details_list_item, null);
        }
        TextView txtListChild = (TextView) convertView
                .findViewById(R.id.lblListItem);

        txtListChild.setText(childText.getEmpName());
        return convertView;

    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition))
                .size();

    }

    @Override
    public Object getGroup(int groupPosition) {
        return this._listDataHeader.get(groupPosition);
    }

    @Override
    public int getGroupCount() {
        return this._listDataHeader.size();
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded,
            View convertView, ViewGroup parent) {
        //String headerTitle = (String) getGroup(groupPosition);
        Level1 headeTitle = (Level1) getGroup(groupPosition);
        if (convertView == null) {
            LayoutInflater infalInflater = (LayoutInflater) this._context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(
                    R.layout.team_details_list_group, null);
        }
        TextView lblListHeader = (TextView) convertView
                .findViewById(R.id.lblListHeader);
        //lblListHeader.setTypeface(null, Typeface.BOLD);
        lblListHeader.setText(headeTitle.getEmpName());

        return convertView;
    }

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

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

---

Level1 Model class

public class Level1 {

    private String empId = "";
    private String empName = "";



    public String getEmpId() {
        return empId;
    }

    public void setEmpId(String empId) {
        this.empId = empId;
    }

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

}

---

2级模型类

public class Level2 {

    private String empId= "";
    private String empName = "";



    public String getEmpId() {
        return empId;
    }
    public void setEmpId(String empId) {
        this.empId = empId;
    }
    public String getEmpName() {
        return empName;
    }
    public void setEmpName(String empName) {
        this.empName = empName;
    }


}

请帮帮我。我陷入了困境。

被修改

以下是日志猫：

下面是logcat：

 FATAL EXCEPTION: main
 java.lang.NullPointerException
     at com.XXXXXXXX.XXXXXXXX.TeamDetailsAdapter.getChildrenCount(TeamDetailsAdapter.java:78)
     at android.widget.ExpandableListConnector.refreshExpGroupMetadataList(ExpandableListConnector.java:561)
     at android.widget.ExpandableListConnector.expandGroup(ExpandableListConnector.java:682)
     at android.widget.ExpandableListView.handleItemClick(ExpandableListView.java:567)
     at android.widget.ExpandableListView.performItemClick(ExpandableListView.java:527)
     at android.widget.AbsListView$PerformClick.run(AbsListView.java:1696)
     at android.os.Handler.handleCallback(Handler.java:587)
     at android.os.Handler.dispatchMessage(Handler.java:92)
     at android.os.Looper.loop(Looper.java:123)
     at android.app.ActivityThread.main(ActivityThread.java:4627)
     at java.lang.reflect.Method.invokeNative(Native Method)
     at java.lang.reflect.Method.invoke(Method.java:521)
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)