AsyncTask/Android线程开始android程序员

Question

我正在开发一个android应用程序。它必须从基于json的互联网上阅读一些内容。那么我现在已经明白了这一点。但是，当我测试我的应用程序时，该应用程序卡在下载Feed的部分。用户界面卡住了几秒钟。

我已经搞清楚了，我需要使用Android中的AsyncTask类来在后台运行连接。我在这个主题上阅读了很多，我几乎可以梦想这个理论。现在把它付诸实践，它给了我一点问题。

该应用程序现在有一大堆类，但处理下载Feed的类（活动）并将retreived数据放入listView中。该类称为KVONieuws（荷兰的志愿 - 新闻）这里的源：

package com.appsoweb.kvodeventer; 

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

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

import com.appsoweb.kvodeventer.JSONfunctions; 
import com.appsoweb.kvodeventer.KVONieuws; 
import com.appsoweb.kvodeventer.R; 

import android.app.ListActivity; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.Toast; 
import android.widget.AdapterView.OnItemClickListener; 

public class KVONieuws extends ListActivity { 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.listplaceholder); 

     ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>(); 

     JSONObject json = JSONfunctions.getJSONfromURL("http://crossalertdeventer.nl/api/news.json"); 

     try{ 

      JSONArray earthquakes = json.getJSONArray("items"); 

      for(int i=0;i<earthquakes.length();i++){       
       HashMap<String, String> map = new HashMap<String, String>();  
       JSONObject e = earthquakes.getJSONObject(i); 

       map.put("id", String.valueOf(i)); 
       map.put("name", "Titel:" + e.getString("title")); 
       map.put("image", "Image: " + e.getString("image")); 
       mylist.add(map);    
      }  
     }catch(JSONException e)  { 
      Log.e("log_tag", "Parsing error "+e.toString()); 
     } 


     ListAdapter adapter = new SimpleAdapter(this, mylist , R.layout.singlelistitem, 
         new String[] { "name", "image" }, 
         new int[] { R.id.item_title, R.id.item_subtitle }); 

     setListAdapter(adapter); 

     final ListView lv = getListView(); 
     lv.setTextFilterEnabled(true); 
     lv.setOnItemClickListener(new OnItemClickListener() { 
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) {    
       @SuppressWarnings("unchecked") 
       HashMap<String, String> o = (HashMap<String, String>) lv.getItemAtPosition(position);     
       Toast.makeText(KVONieuws.this, "ID '" + o.get("id") + "' was clicked.", Toast.LENGTH_SHORT).show(); 

      } 
     }); 
    } 
} 

现在我已经创建了一个名为JSONfunctions.java这里另一个类来处理故事的JSON部分：

package com.appsoweb.kvodeventer; 

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

import org.apache.http.HttpEntity; 
import org.apache.http.HttpResponse; 
import org.apache.http.client.HttpClient; 
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 JSONfunctions { 

    public static JSONObject getJSONfromURL(String url){ 
     InputStream is = null; 
     String result = ""; 
     JSONObject jArray = null; 

     //http post 
     try{ 
       HttpClient httpclient = new DefaultHttpClient(); 
       HttpPost httppost = new HttpPost(url); 
       httppost.setHeader("User-Agent", "9fb01091b51527555d1d3fc87709918f"); 
       HttpResponse response = httpclient.execute(httppost); 
       HttpEntity entity = response.getEntity(); 
       is = entity.getContent(); 

     }catch(Exception e){ 
       Log.e("log_tag", "Error in http connection "+e.toString()); 
     } 

     //convert response to string 
     try{ 
       BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8); 
       StringBuilder sb = new StringBuilder(); 
       String line = null; 
       while ((line = reader.readLine()) != null) { 
         sb.append(line + "\n"); 
       } 
       is.close(); 
       result=sb.toString(); 
     }catch(Exception e){ 
       Log.e("log_tag", "Error converting result "+e.toString()); 
     } 

     try{ 

      jArray = new JSONObject(result);    
     }catch(JSONException e){ 
       Log.e("log_tag", "Error parsing data "+e.toString()); 
     } 

     return jArray; 
    } 
} 

现在我已经尝试了很多这样的代码来使（重部分）作为背景中的线程运行，并且我理解它的理论，但我无法完成它的工作。我不知道为什么....

有没有人可以简单地调整我的代码或指示实现内部类的地方也许扩展AsyncTask类，并给出一个想法在哪里放置什么代码在后台运行的方法和onpostexecute ...

感谢任何人会帮助我！

Answer 1

呼叫new MyRssReadTask().execute();在onCreate方法...

See this Link

class MyRssReadTask extends AsyncTask<Void, Void, JSONObject> { 
     ProgressDialog waitingDialog; 
     @Override 
     protected void onPreExecute() { 
      waitingDialog = new ProgressDialog(KVONieuws.this); 
      waitingDialog.setMessage("Loading..."); 
      waitingDialog.show(); 
      super.onPreExecute(); 
     } 

     @Override 
     protected Void doInBackground(Void... unused) { 

      JSONObject json = JSONfunctions.getJSONfromURL("http://crossalertdeventer.nl/api/news.json"); 

      return json; 
     } 

     @Override 
     protected void onPostExecute(JSONObject objJson) { 
      super.onPostExecute(result); 
      if(waitingDialog.isshowing()){ 
      waitingDialog.dismiss();} 

      //do stuff here 
      JSONArray earthquakes = objJson.getJSONArray("items"); 
     } 
    }