异步加载JSON列表视图

你好，我有这段代码，它给了我Android 3和4设备上的错误。我知道我可以用async解决这个问题，但是我之前没有和sync任务一起工作过，也不知道它是如何工作的。有人可以给我一个例子与我的代码或建议如何实现它？异步加载JSON列表视图

我的代码：

package com.wemait.obd.emmen; 

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

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

import com.wemait.obd.emmen.JSONParser; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.AdapterView.OnItemClickListener; 
import android.widget.ListView; 

public class Nieuws extends Activity { 


// url om request te maken 
private static String URL = "http://www.iappministrator.com/OBDE/webservice/android_news_items.php"; 

// JSON Node namen 
static final String TAG_ITEMS = "items"; 
static final String TAG_TITLE = "title"; 
static final String TAG_MESSAGE = "message"; 
static final String TAG_DATE = "date"; 
static final String TAG_IMAGES = "images"; 

// Nieuws JSONArray 
JSONArray newsArray = null; 

ListView list; 
LazyAdapter adapter; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.nieuws); 

    // Hashmap voor listView 
    final ArrayList<HashMap<String, String>> newsList = new ArrayList<HashMap<String, String>>(); 

    // Maak een JSON Parser instance 
    JSONParser jParser = new JSONParser(); 

    // Pakt JSON string uit URL 
    JSONObject json = jParser.getJSONFromUrl(URL); 

    try{ 
     // Pakt de Array van Nieuwsartikelen 
     newsArray = json.getJSONArray(TAG_ITEMS); 

     // Loop door alle Nieuwsartikels 
     for(int i=0; i < newsArray.length(); i++){ 
      JSONObject c = newsArray.getJSONObject(i); 

      // Het plaatsen van elk json item in variabele 
      String title = c.getString(TAG_TITLE); 
      String message = c.getString(TAG_MESSAGE); 
      //String date = c.getString(TAG_DATE); 
      String images = c.getString(TAG_IMAGES); 

      // maak een nieuwe HashMap 
      HashMap<String, String> map = new HashMap<String, String>(); 

      // voeg elk item child node in de Hashmap -> value 
      map.put(TAG_TITLE, title); 
      map.put(TAG_MESSAGE, message); 
      //map.put(TAG_DATE, date); 
      map.put(TAG_IMAGES, images); 


      // voeg de HashList toe aan ArrayList 
      newsList.add(map); 
     } 
    } catch(JSONException e){ 
     e.printStackTrace(); 
    } 


    list=(ListView)findViewById(R.id.list); 

    adapter=new LazyAdapter(this, newsList, R.layout.list_row, 
      new String[]{TAG_TITLE, TAG_MESSAGE, TAG_DATE, TAG_IMAGES}, new int[] { 
      R.id.title, R.id.artist, R.id.duration, R.id.list_image});   
    list.setAdapter(adapter); 


    // Click event for single list row 
    list.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> parent, View view, 
       int position, long id) { 
       HashMap<String, String> map = newsList.get(position); 

      Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); 
      //Intent in = new Intent(SingleMenuItemActivity.this, org.scout.android.library.LibraryDetail.class); 
      in.putExtra(TAG_TITLE, map.get(TAG_TITLE)); 
      in.putExtra(TAG_MESSAGE, map.get(TAG_MESSAGE));       
      in.putExtra(TAG_DATE, map.get(TAG_DATE)); 
      in.putExtra(TAG_IMAGES, map.get(TAG_IMAGES)); 

      startActivity(in); 
     /* old code public void onItemClick(AdapterView<?> parent, View view, 
       int position, long id) { 


      String title = ((TextView) view.findViewById(R.id.title)).getText().toString(); 
      String date = ((TextView) view.findViewById(R.id.duration)).getText().toString(); 
      String message = ((TextView) view.findViewById(R.id.artist)).getText().toString(); 
      //String images = ((TextView) view.findViewById(R.id.list_image)).getText().toString(); 
      //ImageView thumb_image = (ImageView) view.findViewById(R.id.thumbnail); // thumb image 
      String images = ((ImageView)view.findViewById(R.id.list_image)).getImageMatrix().toString(); 
      //String images = ((ImageView)view.findViewById(R.id.list_image)).toString(); 
      //String images = ((ImageView)view.findViewById(R.id.list_image)).getContext().toString(); 

      // Start de nieuwe intent 

      Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); 
      //Bitmap bitmap = (Bitmap) in.getParcelableExtra(TAG_IMAGES); 

      in.putExtra(TAG_TITLE, title); 
      in.putExtra(TAG_DATE, date); 
      in.putExtra(TAG_MESSAGE, message); 
      in.putExtra(TAG_IMAGES, images); 
      startActivity(in);*/ 

     } 
    });  
}

}

我收到的错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wemait.obd.emmen/com.wemait.obd.emmen.Nieuws}: android.os.NetworkOnMainThreadException 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992) 
at android.app.ActivityThread.access$600(ActivityThread.java:127) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158) 
at android.os.Handler.dispatchMessage(Handler.java:99) 
at android.os.Looper.loop(Looper.java:137) 
at android.app.ActivityThread.main(ActivityThread.java:4511) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:511) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747) 
at dalvik.system.NativeStart.main(Native Method) 
Caused by: android.os.NetworkOnMainThreadException 
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099) 
at java.net.InetAddress.lookupHostByName(InetAddress.java:391) 
at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242) 
at java.net.InetAddress.getAllByName(InetAddress.java:220) 
at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137) 
at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) 
at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) 
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360) 
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) 
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487) 
at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465) 
at com.wemait.obd.emmen.JSONParser.getJSONFromUrl(JSONParser.java:38) 
at com.wemait.obd.emmen.Nieuws.onCreate(Nieuws.java:53) 
at android.app.Activity.performCreate(Activity.java:4470) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)

我的适配器类：

package com.wemait.obd.emmen; 

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

import android.app.Activity; 
import android.content.Context; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.BaseAdapter; 
import android.widget.ImageView; 
import android.widget.TextView; 

public class LazyAdapter extends BaseAdapter { 

    private Activity activity; 
    private ArrayList<HashMap<String, String>> data; 
    private static LayoutInflater inflater=null; 
    public ImageLoader imageLoader; 

    public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d, int listRow, String[] strings, int[] is) { 
     activity = a; 
     data=d; 
     inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     imageLoader=new ImageLoader(activity.getApplicationContext()); 
    } 

    public int getCount() { 
     return data.size(); 
    } 

    public Object getItem(int position) { 
     return position; 
    } 

    public long getItemId(int position) { 
     return position; 
    } 

    public View getView(int position, View convertView, ViewGroup parent) { 
     View vi=convertView; 
     if(convertView==null) 
      vi = inflater.inflate(R.layout.list_row, null); 

     TextView title = (TextView)vi.findViewById(R.id.title); // title 
     TextView artist = (TextView)vi.findViewById(R.id.artist); // artist name 
     TextView duration = (TextView)vi.findViewById(R.id.duration); // duration 
     ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image 

     HashMap<String, String> song = new HashMap<String, String>(); 
     song = data.get(position); 

     // Setting all values in listview 
     title.setText(song.get(CustomizedListView.TAG_TITLE)); 
     artist.setText(song.get(CustomizedListView.TAG_MESSAGE)); 
     duration.setText(song.get(CustomizedListView.TAG_DATE)); 
     imageLoader.DisplayImage(song.get(CustomizedListView.TAG_IMAGES), thumb_image); 
     return vi; 
    } 
}

来源

2012-10-27 ddnl

的Android 3和4此限制。您不能在主线程上运行任何与网络相关的任务。您必须为此创建单独的线程或使用异步任务。我会推荐AsynTask，但如果你想通过线程解决这个问题，那么使用线程和处理程序来实现它。这是你的代码将看怎么样，如果你要使用AsynTask :)

public class Nieuws extends Activity{ 
private static String URL = "http://www.iappministrator.com/OBDE/webservice/android_news_items.php"; 

// JSON Node namen 
static final String TAG_ITEMS = "items"; 
static final String TAG_TITLE = "title"; 
static final String TAG_MESSAGE = "message"; 
static final String TAG_DATE = "date"; 
static final String TAG_IMAGES = "images"; 

// Nieuws JSONArray 
JSONArray newsArray = null; 

ListView list; 
LazyAdapter adapter; 

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.nieuws); 
    list=(ListView)findViewById(R.id.list); 

    new GetJSONData().execute(); 

} 

class GetJSONData extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>>{ 

@Override 
protected ArrayList<HashMap<String, String>> doInBackground(Void... arg0) { 
    // Hashmap voor listView 
    final ArrayList<HashMap<String, String>> newsList = new ArrayList<HashMap<String, String>>(); 

    // Maak een JSON Parser instance 
    JSONParser jParser = new JSONParser(); 

    // Pakt JSON string uit URL 
    JSONObject json = jParser.getJSONFromUrl(URL); 

    try{ 
     // Pakt de Array van Nieuwsartikelen 
     newsArray = json.getJSONArray(TAG_ITEMS); 

     // Loop door alle Nieuwsartikels 
     for(int i=0; i < newsArray.length(); i++){ 
      JSONObject c = newsArray.getJSONObject(i); 

      // Het plaatsen van elk json item in variabele 
      String title = c.getString(TAG_TITLE); 
      String message = c.getString(TAG_MESSAGE); 
      //String date = c.getString(TAG_DATE); 
      String images = c.getString(TAG_IMAGES); 

      // maak een nieuwe HashMap 
      HashMap<String, String> map = new HashMap<String, String>(); 

      // voeg elk item child node in de Hashmap -> value 
      map.put(TAG_TITLE, title); 
      map.put(TAG_MESSAGE, message); 
      //map.put(TAG_DATE, date); 
      map.put(TAG_IMAGES, images); 


      // voeg de HashList toe aan ArrayList 
      newsList.add(map); 
     } 
    } catch(JSONException e){ 
     e.printStackTrace(); 
    } 
    return newsList; 
} 
@Override 
protected void onPostExecute(ArrayList<HashMap<String, String>> result) { 



    adapter=new LazyAdapter(this, result, R.layout.list_row, 
      new String[]{TAG_TITLE, TAG_MESSAGE, TAG_DATE, TAG_IMAGES}, new int[] { 
      R.id.title, R.id.artist, R.id.duration, R.id.list_image});   
    list.setAdapter(adapter); 


    // Click event for single list row 
    list.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> parent, View view, 
       int position, long id) { 
       HashMap<String, String> map = newsList.get(position); 

      Intent in = new Intent(getApplicationContext(), SingleMenuItemActivity.class); 
      //Intent in = new Intent(SingleMenuItemActivity.this, org.scout.android.library.LibraryDetail.class); 
      in.putExtra(TAG_TITLE, map.get(TAG_TITLE)); 
      in.putExtra(TAG_MESSAGE, map.get(TAG_MESSAGE));       
      in.putExtra(TAG_DATE, map.get(TAG_DATE)); 
      in.putExtra(TAG_IMAGES, map.get(TAG_IMAGES)); 

      startActivity(in); 

     } 
    }); 
} 
} 
}

来源

2012-10-27 10:28:30

我得到通过我lazyAdapter类的一些错误，在\t \t适配器=新LazyAdapter（这一点，因此，R.layout .list_row， \t \t新的String [] {TAG_TITLE，TAG_MESSAGE，TAG_DATE，TAG_IMAGES}，新INT [] { \t \t R.id.title，R.id.artist，R.id.duration，R.id. list_image}）;和newsList.get（位置） – ddnl

请附上错误日志以及 –

我犯了一个错误class_name.this是它。但按钮onclick去第二个活动给我列表视图中的错误 – ddnl

if (android.os.Build.VERSION.SDK_INT > 9) { 
      StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder() 
        .permitAll().build(); 
      StrictMode.setThreadPolicy(policy); 
     }

来源

2012-10-29 10:04:14

将此代码添加到您的创建它也将添加@SuppressLint .....我在SOAP服务中收到相同的错误... –

异步加载JSON列表视图

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