Android應用程序在設備和模擬器上崩潰（線程問題？）

Question

我提出，解析應用程序JSON文件，然后使用URL從JSON文件中的一個，以顯示一束圖像GridView 。 但是，我認為問題在於應用程序在JsonParsing類中查找main方法，因為當我嘗試在模擬器上運行它時，系統甚至沒有在onCreate（）方法中打印第一行代碼。 這可能與線程有關嗎？

05-30 10:21:50.660: I/System.out(867):  We made it this far
05-30 10:21:51.090: D/dalvikvm(867): GC_FOR_ALLOC freed 106K, 6% free 3237K/3412K, paused 47ms, total 48ms
05-30 10:21:51.100: I/dalvikvm-heap(867): Grow heap (frag case) to 4.299MB for 1127536-byte allocation
05-30 10:21:51.350: D/dalvikvm(867): GC_FOR_ALLOC freed 0K, 4% free 4338K/4516K, paused 126ms, total 127ms
05-30 10:21:51.860: D/AndroidRuntime(867): Shutting down VM
05-30 10:21:51.860: W/dalvikvm(867): threadid=1: thread exiting with uncaught exception (group=0xb1a97ba8)
05-30 10:21:51.870: E/AndroidRuntime(867): FATAL EXCEPTION: main
05-30 10:21:51.870: E/AndroidRuntime(867): Process: com.example.bitmapdisplay, PID: 867
05-30 10:21:51.870: E/AndroidRuntime(867): java.lang.RuntimeException: Unable to start activity     ComponentInfo{com.example.bitmapdisplay/com.example.bitmapdisplay.MainActivity}: java.lang.NullPointerException
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.os.Handler.dispatchMessage(Handler.java:102)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.os.Looper.loop(Looper.java:136)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.ActivityThread.main(ActivityThread.java:5017)
05-30 10:21:51.870: E/AndroidRuntime(867):  at java.lang.reflect.Method.invokeNative(Native Method)
05-30 10:21:51.870: E/AndroidRuntime(867):  at java.lang.reflect.Method.invoke(Method.java:515)
05-30 10:21:51.870: E/AndroidRuntime(867):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-30 10:21:51.870: E/AndroidRuntime(867):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-30 10:21:51.870: E/AndroidRuntime(867):  at dalvik.system.NativeStart.main(Native Method)
05-30 10:21:51.870: E/AndroidRuntime(867): Caused by: java.lang.NullPointerException
05-30 10:21:51.870: E/AndroidRuntime(867):  at com.example.bitmapdisplay.MainActivity.fillGridView(MainActivity.java:83)
05-30 10:21:51.870: E/AndroidRuntime(867):  at com.example.bitmapdisplay.MainActivity.onCreate(MainActivity.java:71)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.Activity.performCreate(Activity.java:5231)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-30 10:21:51.870: E/AndroidRuntime(867):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-30 10:21:51.870: E/AndroidRuntime(867):  ... 11 more

這是我的Java代碼（對不起，注釋數量少）

package com.example.bitmapdisplay;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;

import com.fasterxml.jackson.core.JsonParseException;

import android.R;
import android.app.Activity;
import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ArrayAdapter;
import android.widget.GridView;
import android.widget.ImageView;


public class MainActivity extends Activity {

    /**
     * Bitmap items na dimage displaying
     */
    Bitmap image;
    BitmapDrawable bd;
    ImageView temp;
    ProgressDialog pd;

    /**
     * JSON URL
     */
    URL url;

    /**
     * Data from JSON file
     */
    ArrayList<String> urls;
    ArrayList<ImageView> images;

    JsonParsing obj;

    int counter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        System.out.println(" We made it this far");
        super.onCreate(savedInstanceState);
        setContentView(com.example.bitmapdisplay.R.layout.image_container);

        counter = 0;
        images = new ArrayList<ImageView>();


        new TheTask().execute();

        fillGridView();
    }

    /**
     * Fills the ListView
     */
    private void fillGridView() {

        ArrayAdapter<ImageView> adapter = new ArrayAdapter<ImageView>(this, com.example.bitmapdisplay.R.layout.image_container,images);

        GridView grid = (GridView) findViewById(com.example.bitmapdisplay.R.id.gvImages);

        grid.setAdapter(adapter);

    }

    public class URLArray extends AsyncTask<String, Void, Void> {

        @Override
        protected Void doInBackground(String... json_link_str) {

            try {
                URL json_link = new URL("http://api.tumblr.com/v2/blog/humansofnewyork.com/posts?api_key=7ag2CJXOuxuW3vlVS5wQG6pYA6a2ZQcSCjzZsAp2pDbVwf3xEk&notes_info=true&filter=text");

                JsonParsing parse_images = new JsonParsing(json_link, "humansofnewyork");
                try {
                    parse_images.parseFile();
                } catch (JsonParseException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                obj = parse_images;
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            return null;
        }

        protected Void onPostExecute(Void...voids ) {
            urls = obj.urlList;
            return null;
        }

    }


class TheTask extends AsyncTask<Void,Void,Void>
{

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        pd.show();
    }


    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub
        try
        {
            int counter = 0;
        for (ImageView temp : images) {

            image = downloadBitmap(urls.get(counter));
            temp.setImageBitmap(image);
            images.add(temp);
            counter++;
        }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        pd.dismiss();
        if(image!=null)
        {
            fillGridView();
        }

    }   
}
 private Bitmap downloadBitmap(String url) {
     // initilize the default HTTP client object
     final DefaultHttpClient client = new DefaultHttpClient();

     //forming a HttoGet request 
     final HttpGet getRequest = new HttpGet(url);
     try {

         HttpResponse response = client.execute(getRequest);

         //check 200 OK for success
         final int statusCode = response.getStatusLine().getStatusCode();

         if (statusCode != HttpStatus.SC_OK) {
             Log.w("ImageDownloader", "Error " + statusCode + 
                     " while retrieving bitmap from " + url);
             return null;

         }

         final HttpEntity entity = response.getEntity();
         if (entity != null) {
             InputStream inputStream = null;
             try {
                 // getting contents from the stream 
                 inputStream = entity.getContent();

                 // decoding stream data back into image Bitmap that android understands
                 image = BitmapFactory.decodeStream(inputStream);


             } finally {
                 if (inputStream != null) {
                     inputStream.close();
                 }
                 entity.consumeContent();
             }
         }
     } catch (Exception e) {
         // You Could provide a more explicit error message for IOException
         getRequest.abort();
         Log.e("ImageDownloader", "Something went wrong while" +
                 " retrieving bitmap from " + url + e.toString());
     } 

     return image;
 }


}

圖像容器布局XML文件。 它僅用於GridView圖像：

<?xml version="1.0" encoding="utf-8"?>
<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >


</ImageView>

Answer 1

您尚未初始化TheTask異步任務的onPreExecute中使用的pd 。

在onPreExecute在onPreExecute添加pd = new ProgressDialog(MainActivity .this) pd.show