listview的使用----BaseAdapter

public class MainActivity extends Activity {List personList;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                personList = new ArrayList();        //把数据库的数据查询出来        MyOpenHelper oh = new MyOpenHelper(this);        SQLiteDatabase db =  oh.getWritableDatabase();        Cursor cursor = db.query("person", null, null, null, null, null, null, null);        while(cursor.moveToNext()){        String _id = cursor.getString(0);        String name = cursor.getString(1);        String salary = cursor.getString(2);        String phone = cursor.getString(3);                Person p = new Person(_id, name, phone, salary);        personList.add(p);        }                ListView lv = (ListView) findViewById(R.id.lv);        lv.setAdapter(new MyAdapter());    }        class MyAdapter extends BaseAdapter{    //系统调用，用来获知集合中有多少条元素@Overridepublic int getCount() {return personList.size();}//由系统调用，获取一个View对象，作为ListView的条目//position:本次getView方法调用所返回的View对象，在listView中是处于第几个条目，那么position的值就是多少@Overridepublic View getView(int position, View convertView, ViewGroup parent) {Person p = personList.get(position);//TextView tv = new TextView(MainActivity.this);System.out.println("getView调用：" + position + ";" + convertView);//tv.setText(p.toString());//tv.setTextSize(18);View v = null;//判断条目是否有缓存if(convertView == null){//把布局文件填充成一个View对象v = View.inflate(MainActivity.this, R.layout.item_listview, null);}else{v = convertView;}//获取布局填充器对象//LayoutInflater inflater = LayoutInflater.from(MainActivity.this);//使用布局填充器填充布局文件//View v2 = inflater.inflate(R.layout.item_listview, null);//LayoutInflater inflater2 = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);//View v3 = inflater2.inflate(R.layout.item_listview, null);//通过资源id查找组件,注意调用的是View对象的findViewByIdTextView tv_name = (TextView) v.findViewById(R.id.tv_name);tv_name.setText(p.getName());TextView tv_phone = (TextView) v.findViewById(R.id.tv_phone);tv_phone.setText(p.getPhone());TextView tv_salary = (TextView) v.findViewById(R.id.tv_salary);tv_salary.setText(p.getSalary());return v;}@Overridepublic Object getItem(int position) {return null;}@Overridepublic long getItemId(int position) {return 0;}        }    }
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