JSON程序中的空指针异常

Question

我在代码中显示的三行中的两行中得到Null指针异常。请看看它。我是android的初学者。提前致谢。我试过实例化瓷砖JSONarray，但即使这样也行不通。

package pack.assignment;            ***
import java.net.URL;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.InputStream;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.Toast;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import java.io.IOException;
import android.widget.ImageView;
import java.net.MalformedURLException;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.app.Activity;
import android.app.ProgressDialog;

public class Landing extends Activity {
    // url to make request
    private static String url = "http://playup-jo.s3.amazonaws.com/dev/config.json";
    private ProgressDialog pDialog;
    JSONParser jParser = new JSONParser();
    // tiles JSONArray
    JSONArray tiles=null;
    ImageView img;
    // JSON Node names
    private static final String TAG_TILES = "tiles";
    private static final String TAG_IMAGE = "image";
    private static final String TAG_URL = "url";
    private static final String TAG_MDPI = "mdpi";
    private static final String TAG_NAME = "name";

  //  Intent go = new Intent(this, Google.class);

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        // Loading JSON in Background Thread
        new LoadJSON().execute(); 
      img = (ImageView)findViewById(R.id.image);

        // getting JSON string from URL
        JSONObject json = jParser.getJSONFromUrl(url);
    }
    /**
     * Background Async Task to Load all INBOX messages by making HTTP Request
     * */
    class LoadJSON extends AsyncTask<String, String, Bitmap> {
        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(Landing.this);
            pDialog.setMessage("Loading ...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }

        /**
         * getting JSON
         * */
        protected Bitmap doInBackground(String... args) {

            // getting JSON string from URL
            JSONObject json = jParser.getJSONFromUrl(url);
            Bitmap bitmap=null;
            // Check your log cat for JSON reponse
        //    Log.d("JSONNN: ", json.toString());

            try {
                // Getting Array of Tiles
                tiles= new JSONArray();
                tiles = json.getJSONArray(TAG_TILES);            ***

                // looping through All Tiles
                for(int i = 0; i < 1; i++){
                    JSONObject c = tiles.getJSONObject(i);
                    // Storing json item in variable 
                    String name = c.getString(TAG_NAME);
                    // mdpi is again JSONObject
                    JSONObject mdpi= c.getJSONObject(TAG_MDPI);
                    String image=mdpi.getString(TAG_IMAGE);
                    String url=mdpi.getString(TAG_URL);
                    // Using the variable to get the bitmap
                    try {
                          bitmap = BitmapFactory.decodeStream((InputStream)new URL(image).getContent());              
                        } 
                    catch (MalformedURLException e) {
                          e.printStackTrace();
                        } 
                    catch (IOException e) {
                          e.printStackTrace();
                        }
                }
            } 
            catch (JSONException e) {
                e.printStackTrace();
         }
            return bitmap;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(final Bitmap result) {
            // dismiss the dialog after getting all products
            pDialog.dismiss();
            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {
                    /**
                     * Updating parsed JSON data 
                     * */
                      img.setImageBitmap(result);       // Rule:2 Always access UI toolkit for UI thread not worker thread
                      MyEventHandler myEvHandler = new MyEventHandler(); 
                      // making the downloaded image clickable 
                      img.setOnClickListener(myEvHandler);
                }
            });

        }


 } 

    class MyEventHandler implements OnClickListener
    {
        public void onClick(View v)
        {
            if (v instanceof ImageView)
            {
     //           startActivity(go);
            }       
        }


    }
}

Answer 1

错误发生在JSONParser类中，我使用httpPost并获取状态代码405而不是200.我使用了httpGet并且它已经解决了。