onCreate()方法中listView写错了吧，ListView listv = (ListView) findViewById(R.id.listView);这句新建了一个局部ListView对象，而外面的成员 private ListView listView;没有初始化，导致String text = listView.getItemAtPosition(position).toString();异常，

private ListView listView;你只定义了listView这个对象的引用而没有对其进行实例化，on a null object reference
这句话就是表示空对象引用，要给private ListView listView;赋一个对象。

public class ArrActivity extends Activity implements OnItemClickListener,OnScrollListener{

    private ListView listView;

    private SimpleAdapter simpleAdapter;

    private ArrayAdapter<String> arr_adapter;

    List<Map<String,Object>> datalist;

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_arr);

        /**ArrayList*/

//        ListView lv = (ListView)findViewById(R.id.listView);

//        String [] a = {"1","2","3","4"};

//        arr_adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, a);

//        lv.setAdapter(arr_adapter);

        /**SimpleAdapter*/

        ListView listv = (ListView) findViewById(R.id.listView);

        datalist = new ArrayList<Map<String,Object>>();

        String []from = {"icon","title","content"};

        int [] to = {R.id.image,R.id.title,R.id.content};

        simpleAdapter = new SimpleAdapter(this, getData(), R.layout.item, from, to);

        listv.setAdapter(simpleAdapter);

        listv.setOnItemClickListener(this);

        listv.setOnScrollListener(this);

    }

    public List<Map<String,Object>> getData(){

    for (int i = 0; i < 20; i++) {

    Map<String,Object> map = new HashMap<String, Object>();

    map.put("icon", R.drawable.ic_launcher);

    map.put("title", "标题"+ (i+1));

    map.put("content", "内容" + (i+1));

    datalist.add(map);

}

    return datalist;

    }

public void onScroll(AbsListView arg0, int arg1, int arg2, int arg3) {

}

public void onScrollStateChanged(AbsListView arg0, int arg1) {

}

/**此处出错,Logcat报错,

*    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object  

*   android.widget.ListView.getItemAtPosition(int)' on a null object reference 

*/

public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

String text = listView.getItemAtPosition(position).toString();    //position对应的选项

Toast.makeText(ArrActivity.this, text, 3000).show();

}

原因可能是getItemAtPosition那里出了问题,帮忙看一下,谢谢

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