【发布时间】：2012-10-06 07:12:58
【问题描述】：
首先，我要感谢曾经在这个社区中帮助过我的每一个人。
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，所以我尝试在没有 AsyncTask 的情况下执行此操作，并且效果很好。
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 并且没有任何变化。所以你能帮帮我吗。
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;
}
}
最好的问候。
【问题讨论】：
标签： java android json listview android-asynctask