问题描述

list定义的变量一直为空。

这是我的代码：

package com.example.testview;import java.util.ArrayList;import java.util.List;import android.app.Activity;import android.content.ContentResolver;import android.database.Cursor;import android.net.Uri;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.ListView;import android.widget.TextView;public class MainActivity extends Activity {    private ListView lv ;    private List<person> persons;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        persons = new ArrayList<person>();        ContentResolver cr =  this.getContentResolver();        Uri uri = Uri.parse(""content://com.android.contacts/raw_contacts"");        Uri uriData = Uri.parse(""content://com.android.contacts/data"");        Cursor cursor = cr.query(uri new String[] {""contact_id""}    null null null);        while(cursor.moveToNext()){            String id = cursor.getString(0);            if(id != null){                Cursor  dataCursor = cr.query(uriData new String[]{""data1""mimetype""}raw_contact_id=?"" new String [] {id} null);                person per = new  person() ;                while(dataCursor.moveToNext()){                    String data = dataCursor.getString(0);                    String mimetype =dataCursor.getString(1);                    if(""vnd.android.cursor.item/name"".equals(mimetype)){                        per.setName(data);                    }else if (""vnd.android.cursor.item/phone_v2"".equals(mimetype)){                        per.setNumber(data);                    }                }                dataCursor.close();                persons.add(per);            }        }        cursor.close();        lv= (ListView) findViewById(R.id.lv);        lv.setAdapter(new myAdtapter() );    }    private class myAdtapter extends BaseAdapter{        @Override        public int getCount() {            // TODO Auto-generated method stub            return persons.size();        }        @Override        public Object getItem(int position) {            // TODO Auto-generated method stub            return null;        }        @Override        public long getItemId(int position) {            // TODO Auto-generated method stub            return 0;        }        @Override        public View getView(int position View convertView ViewGroup parent) {            // TODO Auto-generated method stub            person per =persons.get(position);            View view = View.inflate(getApplicationContext() R.layout.contect_view null);            TextView et_name = (TextView) findViewById(R.id.name);            TextView et_number = (TextView) findViewById(R.id.number);            et_name.setText(per.getName());            et_number.setText(per.getNumber());            return view;        }    }}

我ｄｅｂｕｇ试了一下，发现persons一直没有显示，为空，就是说我每次传进去的数都没被写入ｐｅｒｓｏｎｓ，请指教。
抛出的是空指针异常

解决方案

检查onCreate和while(cursor.moveToNext())循环有没有被执行。

解决方案二：
persons.add(per);这一句之前把per打印一下