Question

任何人都可以帮我弄清楚为什么我在这里得到NullPointerException？我正在尝试为ExpandableListViewActivity设置适配器。

在下面的代码中，我知道我的数组正在填充对象，但是当我尝试从适配器的getGroupView（）方法中的数组中检索对象时，我得到一个nullpointerexception。

有趣的是，我可以在错误发生之前在代码行中获取对象的name属性。

public class Section extends ExpandableListActivity {

bpsection[] sectionsArray;
bpcategory[][] categoriesArray;
ExpandableListAdapter sectionsAdapter;

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



    LoadCategoriesTask loadingtask = new LoadCategoriesTask();
    loadingtask.execute();



}

private class bpsection {
    public int id;
    public String name;
    public int isadult;

    public bpsection(int _id, String _name, int _isadult) {
        this.id = _id;
        this.name = _name;
        this.isadult = _isadult;
    }

}

private class bpcategory extends bpsection {
    @SuppressWarnings("unused")
    public int section;

    public bpcategory(int _section, int _id, String _name, int _isadult) {
        super(_id, _name, _isadult);
        this.section = _section;
    }
}

/*
 * CUSTOM ADAPTER
 */

public class BPSectionsAdapter extends BaseExpandableListAdapter {

    private LayoutInflater blowMeUp;

    public BPSectionsAdapter(Context context)
    {
        blowMeUp = LayoutInflater.from(context);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return categoriesArray[groupPosition][childPosition];           
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return categoriesArray[groupPosition][childPosition].id;
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return categoriesArray[groupPosition].length;
    }

    @Override
    public Object getGroup(int groupPosition) {
        return sectionsArray[groupPosition];
    }

    @Override
    public int getGroupCount() {
        return sectionsArray.length;
    }

    @Override
    public long getGroupId(int groupPosition) {
        return sectionsArray[groupPosition].id;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded,
            View convertView, ViewGroup parent) {

        View parentView = blowMeUp.inflate(R.layout.itm_section, null);

        TextView tv = (TextView) parentView.findViewById(R.id.sectionView);

        Log.v("BPC", "Getting Group View for Section " + ((bpsection)getGroup(groupPosition)).name);
        if(tv == null)Log.v("BPC", "Text view isnull");
        if(((bpsection)getGroup(groupPosition)) == null)Log.v("BPC", "section is null");

        tv.setText(((bpsection)getGroup(groupPosition)).name);

        return parentView;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition,
            boolean isLastChild, View convertView, ViewGroup parent) {
        View childView = convertView;
        if (childView == null) {
            childView = blowMeUp.inflate(R.layout.itm_category, null);
        }

        TextView tv = (TextView) childView.findViewById(R.id.categoryView);
        tv.setText(((bpcategory) getChild(groupPosition, childPosition)).name);

        return childView;

    }

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

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {

        return false;
    }

}

/*
 * ASYNC TASK
 */

private class LoadCategoriesTask extends AsyncTask<Void, Void, Void> {

    private BPCDB db;

    @Override
    protected void onPostExecute(Void result) {
        sectionsAdapter = new BPSectionsAdapter(Section.this);
        setListAdapter(sectionsAdapter);
    }

    @Override
    protected Void doInBackground(Void... params) {

        ArrayList<bpcategory> categories;

        this.db = new BPCDB(getApplicationContext());

        db.open();
        Cursor c_section = db.getSections();
        if(c_section.getCount() > 1)
            try {
                db.dbhelper.copyDBFromAssets();
                c_section = db.getSections();
            } catch (IOException e) {

                e.printStackTrace();
            }
        sectionsArray = new bpsection[c_section.getCount()]; // We can init
                                                                // now that
                                                                // we have a
                                                                // count
        categoriesArray = new bpcategory[c_section.getCount()][];

        int i = 0;
        for (c_section.moveToFirst(); c_section.moveToNext(); c_section
                .isAfterLast()) {
            bpsection s = new bpsection(c_section.getInt(0), // id
                    c_section.getString(1), // name
                    c_section.getInt(2) // isadult
            );

            sectionsArray[i] = s;

            categories = new ArrayList<bpcategory>(); // Reinitialize
                                                        // category list for
                                                        // each section
                                                        // iteration
            Cursor c_category = db.getCategories(Integer.toString(s.id));

            // The first category of each section will be the "all whatever"
            // of the section
            categories.add(new bpcategory(s.id, 0, "all " + s.name,
                    s.isadult));

            for (c_category.moveToFirst(); c_category.moveToNext(); c_category
                    .isAfterLast()) {
                bpcategory c = new bpcategory(c_category.getInt(1),
                        c_category.getInt(0), c_category.getString(2),
                        c_category.getInt(3));

                categories.add(c);

            } // end of categories loop

            int size = categories.size();
            Log.v("BPC", "Section: " + s.name + "Categories: "+ size);
            categoriesArray[i] = categories.toArray(new bpcategory[size]);

        } // end of section loop
        Log.v("BPC", "Sections: " + sectionsArray.length);
        Log.v("BPC", "Categories: " + categoriesArray.length);
        return null;
    }

}

}

这是LogCat

07-13 06:27:57.719: VERBOSE/BPC(210): Getting Group View for Section services
07-13 06:27:57.719: VERBOSE/BPC(210): section is null
07-13 06:27:57.729: DEBUG/AndroidRuntime(210): Shutting down VM
07-13 06:27:57.729: WARN/dalvikvm(210): threadid=3: thread exiting with uncaught exception (group=0x4001aa28)
07-13 06:27:57.729: ERROR/AndroidRuntime(210): Uncaught handler: thread main exiting due to uncaught exception
07-13 06:27:57.749: ERROR/AndroidRuntime(210): java.lang.NullPointerException
07-13 06:27:57.749: ERROR/AndroidRuntime(210):     at com.mogulsoftware.android.bpcruiser.Section$BPSectionsAdapter.getGroupView(Section.java:117)
07-13 06:27:57.749: ERROR/AndroidRuntime(210):     at android.widget.ExpandableListConnector.getView(ExpandableListConnector.java:446)
07-13 06:27:57.749: ERROR/AndroidRuntime(210):     at android.widget.AbsListView.obtainView(AbsListView.java:1273)
07-13 06:27:57.749: ERROR/AndroidRuntime(210):     at android.widget.ListView.makeAndAddView(ListView.java:1658)
07-13 06:27:57.749: ERROR/AndroidRuntime(210):     at android.widget.ListView.fillDown(ListView.java:637)

提示错误（117）的行是：

tv.setText(((bpsection)getGroup(groupPosition)).name);

感谢任何帮助。

Answer 1

回顾你的日志：

07-13 06:27:57.719: VERBOSE/BPC(210): section is null

第115行编码：

if(((bpsection)getGroup(groupPosition)) == null)Log.v("BPC", "section is null");

然后第117行引发NullPointerException，因为

getGroup(groupPosition)

null，无法访问属性name

Answer 2

当您填充剖面阵列时，请查看您的循环。看起来i不会增加。也许更准确地解释for(...)中的陈述

    int i = 0;
    for (c_section.moveToFirst(); c_section.moveToNext(); c_section
            .isAfterLast()) {
        bpsection s = new bpsection(c_section.getInt(0), // id
                c_section.getString(1), // name
                c_section.getInt(2) // isadult
        );

        sectionsArray[i] = s;

     ...

     }

从getGroupView中的数组转换自定义对象时出现NullPointerException

2 个答案: