Question

我不得不说,在我决定做一些修改之前,它的工作是完全正常的。然而,我所做的修改造成了许多错误,所以我试图逐一取消所有修改。我尽力将它恢复到前一个版本,但还是给我“NullPointerException”的“NullPointerExpendion”,无论是在读RSS () 或从AsyncTash () 调用到 showRSS () 中,这些都来自 AsyncTash () 。之前的版本根本没有发生! 我调试了几个小时, 仍然无法找到线索。任何帮助都会感激!

我的代码如下:

package com.android.rss;

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

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;

import android.app.ListActivity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.TextView;
import android.widget.Toast;

public class RSSProActivity extends ListActivity {
    ProgressDialog progDialog;
    String url ="";

    ArrayList<RSSItem> feed;
    ArrayList<String> links;
    ArrayList<String> titles;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        Bundle bundle = this.getIntent().getExtras();
        super.onCreate(savedInstanceState);
        setContentView(R.layout.rss);
        url = bundle.getString("add");
        startLoadRSS(url);
    }

    private void startLoadRSS(String url){
        new RSS_Load().execute(url);
    }

    //
    private void preReadRSS()
    {
    //  Toast.makeText(this, "Reading RSS, Please wait.", Toast.LENGTH_LONG).show();
        progDialog = new ProgressDialog(this);
        progDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
        progDialog.setTitle("Loading RSS");
        progDialog.setMessage("Please wait...");
        progDialog.show();
    }

        private ArrayList<String> readRSS(String url)
        {
            String title ="";
            String link ="";
            String date ="";
            titles = new ArrayList<String>();
            titles.add("KNS");
            // Initializing instance variables
            //feed = new ArrayList<RSSItem>();
            try{
            URL linkUrl = new URL(url);

            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
                factory.setNamespaceAware(false);
                XmlPullParser xpp = factory.newPullParser();

                    // We will get the XML from an input stream
                xpp.setInput(getInputStream(linkUrl), "UTF_8");

                    /* We will parse the XML content looking for the "<title>" tag which appears inside the "<item>" tag.
                     * However, we should take in consideration that the rss feed name also is enclosed in a "<title>" tag.
                     * As we know, every feed begins with these lines: "<channel><title>Feed_Name</title>...."
                     * so we should skip the "<title>" tag which is a child of "<channel>" tag,
                     * and take in consideration only "<title>" tag which is a child of "<item>"
                     *
                     * In order to achieve this, we will make use of a boolean variable.
                     */
                boolean insideItem = false;

                    // Returns the type of current event: START_TAG, END_TAG, etc..
                int eventType = xpp.getEventType();
                while (eventType != XmlPullParser.END_DOCUMENT) {
                    if (eventType == XmlPullParser.START_TAG) {

                        if (xpp.getName().equalsIgnoreCase("item")) {
                            insideItem = true;
                        } else if (xpp.getName().equalsIgnoreCase("title")) {
                            if (insideItem)
                                titles.add(xpp.nextText()); //extract the headline
                        } else if (xpp.getName().equalsIgnoreCase("link")) {
                            if (insideItem)
                                links.add(xpp.nextText()); //extract the link of article
                        }
                    }else if(eventType==XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")){
                        insideItem=false;
                    }
                    eventType = xpp.next(); //move to next element
                }

            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (XmlPullParserException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
                return titles;
            }

         private InputStream getInputStream(URL url)
         {
            try {
                return url.openConnection().getInputStream();
            } catch (IOException e) {
                return null;
            }
         }

        private void displayRSS()
        {
            progDialog.dismiss();

          //  String str [] = (String []) headlines.toArray (new String [headlines.size()]);
            TextView textView = new TextView(this);
    //        int num = titles.size();
    //        String n = Integer.toString(num);
        //  textView.setText(n + "items found.");

            // Data binding
            try{
            ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, titles);
            setListAdapter(adapter);
            }catch(NullPointerException e)
            {
                e.printStackTrace();
            }
            Toast.makeText(this, url, Toast.LENGTH_LONG).show();
        }
    /**    
        @Override
        protected void onListItemClick(ListView l, View v, int position, long id) {
          Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(links.get(position)));
          startActivity(browserIntent);

        }

        **/
        //Asynchronous Task for downloading the RSS Feed.
        public class RSS_Load extends AsyncTask<String, Void, Void>{
           @Override
           protected void onPreExecute() {
              super.onPreExecute();
              preReadRSS();
           }

           @Override
           protected Void doInBackground(String... url) {
             readRSS(url[0]);
               return null;
           }

           @Override
           protected void onProgressUpdate(Void... progress) {
            //  progDialog.setProgress();

           }

           @Override
           protected void onPostExecute(Void result) {
              super.onPostExecute(result);
            displayRSS();

           }

           //display progress bar here.
           public void displayProgressBar(String status){
             //todo
     }


 }
}

logCat 文件 :

    05-25 06:07:13.406: D/dalvikvm(331): GC_EXTERNAL_ALLOC freed 49K, 53% free 2550K/5379K, external 1625K/2137K, paused 43ms
05-25 06:07:13.586: D/dalvikvm(331): GC_EXTERNAL_ALLOC freed 1K, 53% free 2549K/5379K, external 2563K/3200K, paused 40ms
05-25 06:07:29.416: W/dalvikvm(331): threadid=9: thread exiting with uncaught exception (group=0x40015560)
05-25 06:07:29.456: E/AndroidRuntime(331): FATAL EXCEPTION: AsyncTask #1
05-25 06:07:29.456: E/AndroidRuntime(331): java.lang.RuntimeException: An error occured while executing doInBackground()
05-25 06:07:29.456: E/AndroidRuntime(331):  at android.os.AsyncTask$3.done(AsyncTask.java:200)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.FutureTask.run(FutureTask.java:138)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.lang.Thread.run(Thread.java:1019)
05-25 06:07:29.456: E/AndroidRuntime(331): Caused by: java.lang.NullPointerException
05-25 06:07:29.456: E/AndroidRuntime(331):  at com.android.rss.RSSProActivity.readRSS(RSSProActivity.java:88)
05-25 06:07:29.456: E/AndroidRuntime(331):  at com.android.rss.RSSProActivity.access$1(RSSProActivity.java:54)
05-25 06:07:29.456: E/AndroidRuntime(331):  at com.android.rss.RSSProActivity$RSS_Load.doInBackground(RSSProActivity.java:154)
05-25 06:07:29.456: E/AndroidRuntime(331):  at com.android.rss.RSSProActivity$RSS_Load.doInBackground(RSSProActivity.java:1)
05-25 06:07:29.456: E/AndroidRuntime(331):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
05-25 06:07:29.456: E/AndroidRuntime(331):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
05-25 06:07:29.456: E/AndroidRuntime(331):  ... 4 more
05-25 06:07:31.809: E/WindowManager(331): Activity com.android.rss.RSSProActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40526cd0 that was originally added here
05-25 06:07:31.809: E/WindowManager(331): android.view.WindowLeaked: Activity com.android.rss.RSSProActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40526cd0 that was originally added here
05-25 06:07:31.809: E/WindowManager(331):   at android.view.ViewRoot.<init>(ViewRoot.java:258)
05-25 06:07:31.809: E/WindowManager(331):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:148)
05-25 06:07:31.809: E/WindowManager(331):   at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
05-25 06:07:31.809: E/WindowManager(331):   at android.view.Window$LocalWindowManager.addView(Window.java:424)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.Dialog.show(Dialog.java:241)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.rss.RSSProActivity.preReadRSS(RSSProActivity.java:51)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.rss.RSSProActivity.access$0(RSSProActivity.java:44)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.rss.RSSProActivity$RSS_Load.onPreExecute(RSSProActivity.java:149)
05-25 06:07:31.809: E/WindowManager(331):   at android.os.AsyncTask.execute(AsyncTask.java:391)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.rss.RSSProActivity.startLoadRSS(RSSProActivity.java:40)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.rss.RSSProActivity.onCreate(RSSProActivity.java:36)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
05-25 06:07:31.809: E/WindowManager(331):   at android.os.Handler.dispatchMessage(Handler.java:99)
05-25 06:07:31.809: E/WindowManager(331):   at android.os.Looper.loop(Looper.java:123)
05-25 06:07:31.809: E/WindowManager(331):   at android.app.ActivityThread.main(ActivityThread.java:3683)
05-25 06:07:31.809: E/WindowManager(331):   at java.lang.reflect.Method.invokeNative(Native Method)
05-25 06:07:31.809: E/WindowManager(331):   at java.lang.reflect.Method.invoke(Method.java:507)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
05-25 06:07:31.809: E/WindowManager(331):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
05-25 06:07:31.809: E/WindowManager(331):   at dalvik.system.NativeStart.main(Native Method)

Answer 1

您所看到的错误, NetworkOnMainThreadException 基本上意味着它所说的, 您正在尝试在主线上做一些网络活动。

http://developmenter.android.com/reference/android/os/NetworkOnMainThreadExpendion.html" rel=“nofollow”>文件:

The exception that is thrown when an application attempts to perform a networking operation on its main thread.

This is only thrown for applications targeting the Honeycomb SDK or higher. Applications targeting earlier SDK versions are allowed to do networking on their main event loop threads, but it s heavily discouraged. See the document Designing for Responsiveness.

另见《严格模式》。

d 建议将 readRss () 方法移入asynctask。

友情链接