Java 在主线程上解析XML，但通过AsyncTask下载-“无效流或编码：android.os.NetworkOnMainThreadException”

所以我想我花了一整天的时间试图找到一种方法来下载xml文件，并通过XMLPullParser对其进行解析，然后将内容显示到ListView中。我不知道为什么会出现这个系统错误，因为我正在异步任务中下载XML。我应该将解析移到AYSNTASK中吗？这似乎不是必须的

这是我的密码：

public class MainActivity extends Activity {

    ListView lvNewsItems;
    NewsItemAdapter newsItemAdapter;
    ArrayList<NewsItem> newsItems;
    NewsItem item;
    InputStream urlInputStream;

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

        lvNewsItems = (ListView)findViewById(R.id.lv_newsItems);

        // Initializing instance variables
        newsItems = new ArrayList<NewsItem>();

        try {
            new URLAsyncTask().execute(new URL("http://feeds.feedburner.com/SterlingClassicalSchool?format=xml"));
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }

    }

    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    public void ParseXMLAndShowIt(InputStream stream) {
        try {
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
            factory.setNamespaceAware(false);
            XmlPullParser xpp = factory.newPullParser();

            // We will get the XML from an input stream
            xpp.setInput(stream, "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;
                        item = new NewsItem();
                    } else if (xpp.getName().equalsIgnoreCase("title")) {
                        if (insideItem)
                            item.title = xpp.nextText();
                    } 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;
                    newsItems.add(item);
                }
                eventType = xpp.next(); //move to next element
            }

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

        newsItemAdapter = new NewsItemAdapter(this, R.layout.news_item, newsItems);

        lvNewsItems.setAdapter(newsItemAdapter);

    }

    private class URLAsyncTask extends AsyncTask<URL, String, InputStream> {
        // Use the URL passed in the AysncClass and return an InputStream to be used in onPostExecute
        @Override
        protected InputStream doInBackground(URL... params) {
            try {
                Log.v("APP", "Downloading File");
                return params[0].openConnection().getInputStream();
            } catch (IOException e) {
                return null;
            }
        }

        @Override
        protected void onPostExecute(InputStream inputStream) {
            Log.v("APP", "Done downloading now parse it");
            ParseXMLAndShowIt(inputStream);
        }
    }

}

我不知道为什么会出现这个系统错误，因为我正在异步任务中下载XML

不，你不是。您正在后台线程上打开一个流。您正在主应用程序线程上读取流

我应该将解析移到AYSNTASK中吗

您应该从现有异步任务的doInBackground中打开连接、下载和解析XML。只有最后两行是属于onPostExecute的解析方法，在这两行中填充ListView

我不知道为什么会出现这个系统错误，因为我正在异步任务中下载XML

不，你不是。您正在后台线程上打开一个流。您正在主应用程序线程上读取流

我应该将解析移到AYSNTASK中吗

---

您应该从现有异步任务的doInBackground中打开连接、下载和解析XML。onPostExecute中的解析方法只有最后两行，您在这两行中填充ListView。

您不是在异步任务中下载，而是在打开连接。因此，当我在xmlparser上设置输入时，下载会发生吗？您不是在异步任务中下载，你只是在打开连接。那么，当我在xmlparser上设置输入时，下载会发生吗？啊，好吧，我想我误解了调用GetInputStream时会发生什么，所以我可以从中了解到，当我将流传递到xmlparser时，实际发生的下载是什么？@DoubleElite:是的。打开流并不是下载所有内容。毕竟，您可能没有所有内容的堆空间。相反，当您从流中读取数据时，字节会被下载。我是否应该在将结果发布到listview后关闭流？@DoubleElite:可能吧。解析器可能会为您关闭它，但除非有文档记录，否则您应该自己关闭它才能确定。啊，好吧，我想我误解了调用GetInputStream时发生的事情，所以我可以从中了解到，当我将流传递给xmlparser时，实际发生的下载是什么？@DoubleElite:是的。打开流并不是下载所有内容。毕竟，您可能没有所有内容的堆空间。相反，当您从流中读取数据时，字节会被下载。我是否应该在将结果发布到listview后关闭流？@DoubleElite:可能吧。解析器可能会为您关闭它，但除非有文档记录，否则您应该自己关闭它以确保安全。

07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ Invalid stream or encoding: android.os.NetworkOnMainThreadException (position:START_DOCUMENT null@1:1 in java.io.InputStreamReader@426d1398) caused by: android.os.NetworkOnMainThreadException; nested exception is:
07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ android.os.NetworkOnMainThreadException
07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at libcore.io.BlockGuardOs.recvfrom(BlockGuardOs.java:163)
07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at libcore.io.IoBridge.recvfrom(IoBridge.java:506)
07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.net.PlainSocketImpl.read(PlainSocketImpl.java:488)
07-01 15:49:27.773  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.net.PlainSocketImpl.access$000(PlainSocketImpl.java:46)
07-01 15:49:27.783  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.net.PlainSocketImpl$PlainSocketInputStream.read(PlainSocketImpl.java:240)
07-01 15:49:27.783  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.io.BufferedInputStream.read(BufferedInputStream.java:283)
07-01 15:49:27.783  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at com.android.okhttp.internal.http.HttpTransport$ChunkedInputStream.read(HttpTransport.java:441)
07-01 15:49:27.783  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.io.InputStreamReader.read(InputStreamReader.java:233)
07-01 15:49:27.783  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at org.kxml2.io.KXmlParser.fillBuffer(KXmlParser.java:1506)
07-01 15:49:27.783  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at org.kxml2.io.KXmlParser.peekCharacter(KXmlParser.java:1460)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at org.kxml2.io.KXmlParser.setInput(KXmlParser.java:1735)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool.MainActivity.ParseXMLAndShowIt(MainActivity.java:79)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool.MainActivity$URLAsyncTask.onPostExecute(MainActivity.java:142)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool.MainActivity$URLAsyncTask.onPostExecute(MainActivity.java:127)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.os.AsyncTask.finish(AsyncTask.java:632)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.os.AsyncTask.access$600(AsyncTask.java:177)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:102)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.os.Looper.loop(Looper.java:136)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5001)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:515)
07-01 15:49:27.793  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
07-01 15:49:27.803  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
07-01 15:49:27.803  11109-11109/com.doubleelite.sterlingclassicalschoolproject.sterlingclassicalschool W/System.err﹕ at dalvik.system.NativeStart.main(Native Method)