Question

我必须使用AsyncTask用结果填充listview。这是我的代码：

    public class MyActivity extends Activity {
        MainActivity ob;
        String url_connectX = "http://hosr.com/test/getjson.php";
        Httppostaux post;
        JSONArray lststat;

        public JSONArray liststatus() {
            JSONArray jdata=post.getserverdataX(url_connectX);
            return jdata;
        }   

        @Override
        protected void onCreate(Bundle icicle) {
            super.onCreate(icicle);
            setContentView(R.layout.my_new_screen);
            post = new Httppostaux();
            new asyncpost().execute();
        }

//************************************************************************************
        class asyncpost extends AsyncTask< String, String, String > {
            List<String> listContents;      

            protected void onPostExecute(String result) {
               pDialog.dismiss();
               if (result.equals("ok")){
                   ListView myListView = (ListView) findViewById(R.id.ListView1);
                   Log.e("JSON log", "This is my problem = "+listContents);         
                   myListView.setAdapter(new ArrayAdapter<String>(MyActivity.this, android.R.layout.simple_list_item_1, listContents));
                }else{
                   Log.e("JSON log", "ListContents has problems."+listContents);            
                   err_getlista();
                }
            }
            protected String doInBackground(String... params) {
                lststat = liststatus();
                if (lststat != null){                       
                    if (lststat != null && lststat.length() > 0){
                        JSONObject json_data; 
                        try {
                            int length = lststat.length();
                            List<String> listContents = new ArrayList<String>(length);
                            for (int i = 0; i < length; i++)
                            {
                                json_data = lststat.getJSONObject(i);
                                listContents.add(json_data.getString("client_name"));
                            }
                        } catch (Exception e) {
                                Log.e(null, e.toString());
                        }                   
                    }               
                    return "ok"; 
                }else{          
                    return "err";                     
                }
            }
            public void err_getlista(){
                Toast toast1 = Toast.makeText(getApplicationContext(),"Error", Toast.LENGTH_SHORT);
                toast1.show();      
            }   
        }
//************************************************************************************
    }

listContents最终为NULL。为什么？似乎在postExecute的某个地方，listContent的值变为NULL，即使在doInBackGround中似乎有一个非NULL值。我不明白我该如何解决？

Answer 1

您在 doInBackground 中重新声明 listContents 。它是一个局部变量，它优先于类成员。此外，您可能希望确保在列表中检查大小为零的边界

    // should be ...
    // listContents = new ArrayList<String>(length);
    List<String> listContents = new ArrayList<String>(length);
    for (int i = 0; i < length; i++)
    {
        json_data = lststat.getJSONObject(i);
        listContents.add(json_data.getString("client_name"));
    }

AsyncTask结果处理

1 个答案: