Question

我写了这个语句是为了获取媒体描述，只有前50个字符，但我得到了一个例外，这个语句中是否有任何逻辑错误：

String description = ent.getJSONObject(i).
                getJSONObject("media$description").getString("$t").substring(0,49);

enter image description here

Stacktrace：

07-14 09:01:20.510: E/AndroidRuntime(460): FATAL EXCEPTION: main
07-14 09:01:20.510: E/AndroidRuntime(460): java.lang.NullPointerException
07-14 09:01:20.510: E/AndroidRuntime(460):  at com.example.task_10_vedioserach.MainActivity$conn.onPostExecute(MainActivity.java:156)
07-14 09:01:20.510: E/AndroidRuntime(460):  at com.example.task_10_vedioserach.MainActivity$conn.onPostExecute(MainActivity.java:1)
07-14 09:01:20.510: E/AndroidRuntime(460):  at android.os.AsyncTask.finish(AsyncTask.java:417)
07-14 09:01:20.510: E/AndroidRuntime(460):  at android.os.AsyncTask.access$300(AsyncTask.java:127)
07-14 09:01:20.510: E/AndroidRuntime(460):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
07-14 09:01:20.510: E/AndroidRuntime(460):  at android.os.Handler.dispatchMessage(Handler.java:99)
07-14 09:01:20.510: E/AndroidRuntime(460):  at android.os.Looper.loop(Looper.java:123)
07-14 09:01:20.510: E/AndroidRuntime(460):  at android.app.ActivityThread.main(ActivityThread.java:4627)
07-14 09:01:20.510: E/AndroidRuntime(460):  at java.lang.reflect.Method.invokeNative(Native Method)
07-14 09:01:20.510: E/AndroidRuntime(460):  at java.lang.reflect.Method.invoke(Method.java:521)
07-14 09:01:20.510: E/AndroidRuntime(460):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
07-14 09:01:20.510: E/AndroidRuntime(460):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
07-14 09:01:20.510: E/AndroidRuntime(460):  at dalvik.system.NativeStart.main(Native Method)

我的所有代码：

package com.example.task_10_vedioserach;

import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.protocol.HTTP;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONObject;
import org.json.JSONTokener;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ListView;

public class MainActivity extends Activity {

    ListView vediolist;
    ImageButton search;
    Button history;
    EditText title;
    /////////////////
    ArrayList<String > videoInfo; 
    ArrayAdapter< String > Listadapter ; 
    ProgressDialog progress ; 
    /////////////////

      String vedioName;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /////////////////////////////////////////////////////////////////

        vediolist = (ListView) findViewById(R.id.vedioList);
        search = (ImageButton) findViewById(R.id.search);
        history = (Button) findViewById(R.id.history);
        title=(EditText) findViewById(R.id.vedioName);

        /////////////////////////////////////////////////////////////////

        videoInfo = new ArrayList<String>(); 
        Listadapter = new ArrayAdapter<String>(this,    android.R.layout.simple_list_item_1 ,videoInfo);
        progress = new ProgressDialog(this); 
        progress.setMessage("Wait Loading .... "); 
        progress.setCancelable(false); 
        vediolist.setAdapter(new CustomList(MainActivity.this,videoInfo)); 





          search.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {


                vedioName= title.getText().toString();
                new conn().execute("https://gdata.youtube.com/feeds/api/videos?q="+vedioName+"&v=2&alt=json"); 

            }
        });




    }




    class conn extends AsyncTask<String, Integer, String>{


        @Override
        protected void onPreExecute() {

            progress.show(); 
            super.onPreExecute();

        }
        @Override
        protected String doInBackground(String... arg0) {

            String s = GetUrlBody(arg0[0]); 

            return s;
        }

        @Override
        protected void onPostExecute(String result) {

        try{



            JSONObject jo =(JSONObject) new JSONTokener(result).nextValue();


           JSONObject feed = jo.optJSONObject("feed");


           JSONArray ent = feed.optJSONArray("entry");



        for(int i = 0 ; i<ent.length() ; i++){

        String title = ent.getJSONObject(i).
                getJSONObject("title").getString("$t");
        String viewCount = ent.getJSONObject(i).
                getJSONObject("yt$statistics").getString("viewCount");

        String authorName=ent.getJSONObject(i).getJSONArray("author").getJSONObject(0).getJSONObject("name").getString("$t");

        String numDisLikes = ent.getJSONObject(i).
                getJSONObject("yt$rating").getString("numDislikes");

        String numLikes = ent.getJSONObject(i).
                getJSONObject("yt$rating").getString("numLikes");

        String description = ent.getJSONObject(i).
                getJSONObject("media$description").getString("$t").substring(0,49);



        videoInfo.add("Title"+title+"\n"+"By:"+authorName); 


        }



        Listadapter.notifyDataSetChanged();



        }catch(Exception exx) {


             Log.getStackTraceString(exx.getCause().getCause());

        }



            progress.dismiss(); 



            super.onPostExecute(result); 


        } 





        String GetUrlBody (String Url ){


            HttpClient cli = new DefaultHttpClient(); 


            HttpGet g = new HttpGet(Url); 


            try{



            HttpResponse res = cli.execute(g);


            if(res.getStatusLine().getStatusCode() == 200){


                String s =EntityUtils.toString(res.getEntity(), HTTP.UTF_8); 


                return s; 

            }else {



                return "Not Found"; 


            }




            }catch(Exception exx){



                //Log.getStackTraceString(exx.getCause().getCause());


            }

            return null; 
        }





    }



}

Answer 1

您可能尝试访问conn类的onPostExecute（）中第156行具有空值的内容。请查看this link。

希望这会对你有所帮助。如果有任何问题，请回来。

问候..
Sourabh

如何从json文件中获取对象数据

1 个答案: