java - ListView 项目未使用 AsyncTask 加载

Question

首先，我要感谢这个社区中每一位曾经帮助过我的人。

我正在尝试在我的 Activity 中加载 ListView 项目(从服务器下载)。因为我使用的是 GingerBread，所以我尝试在不使用 AsyncTask 的情况下完成它，并且它工作得很好。

当我尝试在 AsyncTask 中执行此操作时，列表仍然为空。 我还尝试将某些部分从 DoInBackground 移动到 onPostExecute，但没有任何变化。所以你能帮助我吗？

这是我的代码(在第二个答案后更新)

MAIN



import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;



import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class StudentMSG extends ListActivity {
    // url to make request
    private static String url = "http://www.xxxxxxxxxxxxx?requsted=xxxxxxxxx";
    // JSON Node names
    private static final String TAG_CONTACTS = "contacts";
    private static final String TAG_ID = "message_id";
    private static final String TAG_NAME = "sender_id";
    private static final String TAG_EMAIL = "title";
    private static final String TAG_ADDRESS = "message_id";
    private static final String TAG_GENDER = "READ";
    private static final String TAG_PHONE = "message_id";
    private static final String TAG_PHONE_MOBILE = "message_id";
    private static final String TAG_PHONE_HOME = "message_id";
    private static final String TAG_PHONE_OFFICE = "message_id";
    ListView lv;
    ArrayList<HashMap<String, String>> contactList ;
    JSONObject json ;
    ListAdapter adapter;
    // contacts JSONArray
    JSONArray contacts = null;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        load task=new load();
        task.execute();





    }



    public class load extends AsyncTask<Void, Void , Void>
    {
        @Override
        protected Void doInBackground(Void... params) {

            // Hashmap for ListView
            contactList = new ArrayList<HashMap<String, String>>();

            // Creating JSON Parser instance
            JSONParser jParser = new JSONParser();

            // getting JSON string from URL
             json = jParser.getJSONFromUrl(url);
                try {
                    contacts = json.getJSONArray(TAG_CONTACTS);
                // looping through All Contacts
                for(int i = 0; i < contacts.length(); i++){
                    JSONObject c = contacts.getJSONObject(i);

                    // Storing each json item in variable
                    String id = c.getString(TAG_ID);
                    String name = c.getString(TAG_NAME);
                    String email = c.getString(TAG_EMAIL);
                    String address = c.getString(TAG_ADDRESS);
                    String gender = c.getString(TAG_GENDER);

                    // Phone number is agin JSON Object


                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_ID, id);
                    map.put(TAG_NAME, name);
                    map.put(TAG_EMAIL, email);
                    map.put(TAG_GENDER, gender);


                    // adding HashList to ArrayList
                    contactList.add(map);
                }
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            return null;



        }
        protected void onPostExecute() {

            String[] s = { TAG_NAME, TAG_EMAIL , TAG_GENDER};
            int[] n = {R.id.name, R.id.email , R.id.mobile };
          adapter = new SimpleAdapter(StudentMSG.this, contactList,R.layout.list_item,s,n );
            setListAdapter(adapter);
    }
}
}

这是 JSON 解析器类

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    public JSONObject getJSONFromUrl(String url) {

        // Making HTTP request
        try {
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);

            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();           

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        //"ISO-8859-1,utf-8;q=0.7,*;q=0.7"
        //"iso-8859-1"
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "utf-8"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;

    }
}

最诚挚的问候。

Answer 1

replace ur code by this=
import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;



import android.app.Activity;
import android.app.ListActivity;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class StudentMSG extends ListActivity {
    // url to make request
    private static String url = "XXXXXXXXXXXXXXXXXXXX/json.php";
    // JSON Node names
    private static final String TAG_CONTACTS = "contacts";
    private static final String TAG_ID = "message_id";
    private static final String TAG_NAME = "sender_id";
    private static final String TAG_EMAIL = "title";
    private static final String TAG_ADDRESS = "message_id";
    private static final String TAG_GENDER = "READ";
    private static final String TAG_PHONE = "message_id";
    private static final String TAG_PHONE_MOBILE = "message_id";
    private static final String TAG_PHONE_HOME = "message_id";
    private static final String TAG_PHONE_OFFICE = "message_id";
    ListView lv;
    ArrayList<HashMap<String, String>> contactList ;
    JSONObject json ;
    ListAdapter adapter;
    // contacts JSONArray
    JSONArray contacts = null;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        load task=new load();
        task.execute();





    }



    public class load extends AsyncTask<Void, Void , Void>
    {
        @Override
        protected Void doInBackground(Void... params) {

            // Hashmap for ListView
            contactList = new ArrayList<HashMap<String, String>>();

            // Creating JSON Parser instance
            JSONParser jParser = new JSONParser();

            // getting JSON string from URL
             json = jParser.getJSONFromUrl(url);
                try {
                    contacts = json.getJSONArray(TAG_CONTACTS);
                // looping through All Contacts
                for(int i = 0; i < contacts.length(); i++){
                    JSONObject c = contacts.getJSONObject(i);

                    // Storing each json item in variable
                    String id = c.getString(TAG_ID);
                    String name = c.getString(TAG_NAME);
                    String email = c.getString(TAG_EMAIL);
                    String address = c.getString(TAG_ADDRESS);
                    String gender = c.getString(TAG_GENDER);

                    // Phone number is agin JSON Object


                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_ID, id);
                    map.put(TAG_NAME, name);
                    map.put(TAG_EMAIL, email);
                    map.put(TAG_GENDER, gender);


                    // adding HashList to ArrayList
                    contactList.add(map);
                }
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            return null;



        }
        protected void onPostExecute() {

            String[] s = { TAG_NAME, TAG_EMAIL , TAG_GENDER};
            int[] n = {R.id.name, R.id.email , R.id.mobile };
          adapter = new SimpleAdapter(StudentMSG.this, contactList,R.layout.list_item,s,n );
            setListAdapter(adapter);

    }
}