如何解決Android應用程序的JSON錯誤？

Question

下面是錯誤日誌：

03-13 10:00:15.778: W/System.err(2558): org.json.JSONException: No value for objects 
03-13 10:00:15.778: W/System.err(2558):  at org.json.JSONObject.get(JSONObject.java:354) 
03-13 10:00:15.778: W/System.err(2558):  at org.json.JSONObject.getJSONArray(JSONObject.java:544) 
03-13 10:00:15.778: W/System.err(2558):  at com.app.Main$ListTask.doInBackground(Main.java:104) 
03-13 10:00:15.778: W/System.err(2558):  at com.app.Main$ListTask.doInBackground(Main.java:1) 
03-13 10:00:15.778: W/System.err(2558):  at android.os.AsyncTask$2.call(AsyncTask.java:287) 
03-13 10:00:15.778: W/System.err(2558):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305) 
03-13 10:00:15.778: W/System.err(2558):  at java.util.concurrent.FutureTask.run(FutureTask.java:137) 
03-13 10:00:15.778: W/System.err(2558):  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
03-13 10:00:15.778: W/System.err(2558):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076) 
03-13 10:00:15.778: W/System.err(2558):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569) 
03-13 10:00:15.778: W/System.err(2558):  at java.lang.Thread.run(Thread.java:856) 

活動代碼

package com.app; 

import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.InputStreamReader; 
import java.util.ArrayList; 
import java.util.Arrays; 

import org.apache.http.HttpResponse; 
import org.apache.http.StatusLine; 
import org.apache.http.client.ClientProtocolException; 
import org.apache.http.client.HttpClient; 
import org.apache.http.client.methods.HttpGet; 
import org.apache.http.impl.client.DefaultHttpClient; 
import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 

import android.os.AsyncTask; 
import android.os.Bundle; 
import android.app.Activity; 
import android.app.ProgressDialog; 
import android.content.Context; 
import android.util.Log; 
import android.view.Menu; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 

public class Main extends Activity { 

    ListView List; 
    ArrayList<String> listArray = new ArrayList<String>(); 
    ArrayAdapter<String> Adapter; 
    Context context; 
    String url = "http://sandzak.today/api/1/categories/?format=json/api/projekti/10?="; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 
     context = this; 
     List = (ListView) findViewById(R.id.lista); 
     Adapter = new ArrayAdapter<String>(this, R.layout.lista, listArray); 
     List.setAdapter(Adapter); 

     VideoListTask loaderTask = new VideoListTask(); 
     loaderTask.execute(); 

    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

    public class VideoListTask extends AsyncTask<Void, Void, Void>{ 

     ProgressDialog dialog; 
     @Override 
     protected void onPreExecute() 
     { 
      dialog = new ProgressDialog(context); 
      dialog.setTitle("Loading Category"); 
      dialog.show(); 
      super.onPreExecute(); 
     } 

     @Override 
     protected Void doInBackground(Void... params) 
     { 
      HttpClient client = new DefaultHttpClient(); 
      HttpGet getRequest = new HttpGet(url); 

      try 
      { 
       HttpResponse responce = client.execute(getRequest); 
       StatusLine statusLine = responce.getStatusLine(); 
       int statusCode = statusLine.getStatusCode(); 

       if(statusCode != 200) 
       { 
        return null; 
       } 

       InputStream jsonStream = responce.getEntity().getContent(); 
       BufferedReader reader = new BufferedReader(new InputStreamReader(jsonStream)); 
       StringBuilder builder = new StringBuilder(); 
       String line; 
       while((line = reader.readLine())!=null) 
       { 
        builder.append(line); 
       } 



       String jsonData = builder.toString(); 

       JSONObject json = new JSONObject(jsonData); 
       JSONObject meta = json.getJSONObject("meta"); 
       JSONArray objects = meta.getJSONArray("objects"); 

       for(int i =0; i<objects.length(); i++) 
       { 
        JSONObject video = objects.getJSONObject(i); 
        listArray.add(video.getString("name")); 
       } 


      } 
      catch (ClientProtocolException e) 
      { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
      catch (IOException e) 
      { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
      catch (JSONException e) 
      { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 

      return null; 
     } 

     @Override 
     protected void onPostExecute(Void result) { 
      dialog.dismiss(); 
      Adapter.notifyDataSetChanged(); 
      super.onPostExecute(result); 
     } 
    } 
} 

我怎樣才能解決這個問題？

Answer 1

在這個節點上創建一個點，你添加字符串，然後將它傳遞給對象。在對象中，你需要傳遞字符串，這是你的json的關鍵詞。

while((line = reader.readLine())!=null) 
       { 
        builder.append(line); 
       } 

Answer 2

1. 他們是一個簡單的方法把一個inputstrem字符串： InputStream inputStream = url.openStream(); Scanner in = new Scanner(inputStream).useDelimiter("\\A"); String str = in.hasNext() ? in.next() : null;

2. 喜歡使用JSONObject.optXxx(field)而非JSONObject.getXxx(field)，這個你根本不需要擔心是否在一個領域json數據還是它可以轉換爲你想要的類型。此外，如果該字段不存在或不能轉化爲特定類型，則JSONObject.optXxx(field, fallback)具有回退值。

3. （可選），如果你想使用JSONObject.getXxx()，您可以先檢查使用JSONObject.has(fieldname)

希望它是有用的無論是在JSON數據歸檔。

Answer 3

更好的是在調用服務時使用responsehandler。

ResponseHandler<String> responseHandler = new BasicResponseHandler(); 
final String responseBody = httpclient.execute(httppost, responseHandler); 

它會直接給我答覆作爲字符串。