android - 应用程序在模拟器中运行良好但显示 networkonmainthread 异常

Question

我创建了一个应用程序，它使用 xml pull 解析器从 url 检索数据。它在模拟器上工作正常，但是当我在选项卡中测试它时，它显示 networkonmainthread 异常。我的代码是:

package com.example.androidsample4;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.res.Resources;
import android.content.res.XmlResourceParser;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class UNIXclass extends Activity 
{
    String unixcommands[];

    AutoCompleteTextView actv1;

    protected URL params;
    static final String URL="http://cympac.com/apps/xmlfile.xml";
    static final String KEY_COMMAND = "command"; // parent node
    static final String KEY_WORD = "word";
    static final String KEY_EXPLANATION = "explanation";


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView tv1=(TextView)findViewById(R.id.textView1);
        AutoCompleteTextView actv=(AutoCompleteTextView)findViewById(R.id.autoCompleteTextView1);
        Button b1=(Button)findViewById(R.id.button1);
        unixcommands=getResources().getStringArray(R.array.Commands);
        ArrayAdapter<String> adapter =new ArrayAdapter<String>(getBaseContext(), android.R.layout.simple_list_item_1,unixcommands);
        actv1 = (AutoCompleteTextView)findViewById(R.id.autoCompleteTextView1);
        actv1.setThreshold(1);
        actv1.setAdapter(adapter);
        b1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) 
            {
                Mytask task=new Mytask();
                task.doInBackground(params);


            }
        });
    }
    private class Mytask extends AsyncTask<java.net.URL, Void, Void>
    {

        @Override
        protected Void doInBackground(java.net.URL... params) 
        {
            TextView myXmlContent = (TextView)findViewById(R.id.textView2);
            String stringXmlContent = null;
            try {
                stringXmlContent = getEventsFromAnXML();   //   54 line
            } catch (XmlPullParserException e) {
                // TODO Auto-generated catch block
                Toast.makeText(getBaseContext(), "error:"+e.getMessage(), Toast.LENGTH_SHORT).show();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Toast.makeText(getBaseContext(), "error:"+e.getMessage(), Toast.LENGTH_SHORT).show();
            }
            myXmlContent.setText(stringXmlContent);
            return null;

        }

    }
    public String getEventsFromAnXML() throws XmlPullParserException,IOException
    {
        StringBuffer stringBuffer=new StringBuffer();

        java.net.URL url=new java.net.URL("http://cympac.com/apps/xmlfile.xml");
        XmlPullParserFactory factory=XmlPullParserFactory.newInstance();
        factory.setNamespaceAware(true);
        XmlPullParser xpp=factory.newPullParser();
        //xpp.setInput(getInputStream(url),"UTF-8");         //84 line
        xpp.setInput(url.openConnection().getInputStream(), "UTF-8");
        int eventType = xpp.getEventType();
        String word = null;

        String tag;
        while ((eventType = xpp.next()) != XmlPullParser.END_DOCUMENT)
        {
            if(XmlPullParser.START_TAG==eventType)
            {
                tag=xpp.getName();
                //stringBuffer.append("\n"+tag);
                if (tag.equals("word"))
                {
                    eventType = xpp.next();
                    word = xpp.getText();
                }
                else if (tag.equals("explanation"))
                {
                    eventType = xpp.next();
                   //if ("cancel".equals(word))
                    if(actv1.getText().toString().equals(word))

                    {
                        stringBuffer.append("\n" + xpp.getText());
                    }
                }

            }

        }
        return stringBuffer.toString();



    }



}

我读到当我们必须使用网络时，我们应该使用 Asynctask。所以我使用了它，但它仍然显示相同的错误。请帮我解决这个问题。logcat o/p

08-21 16:36:41.087 E/AndroidRuntime( 4076): FATAL EXCEPTION: main
08-21 16:36:41.087 E/AndroidRuntime( 4076): android.os.NetworkOnMainThreadException
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1077)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at java.net.InetAddress.lookupHostByName(InetAddress.java:477)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:277)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at java.net.InetAddress.getAllByName(InetAddress.java:249)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:69)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection.<init>(HttpConnection.java:48)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnection$Address.connect(HttpConnection.java:304)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpConnectionPool.get(HttpConnectionPool.java:89)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getHttpConnection(HttpURLConnectionImpl.java:292)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.makeConnection(HttpURLConnectionImpl.java:274)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.retrieveResponse(HttpURLConnectionImpl.java:1038)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at org.apache.harmony.luni.internal.net.www.protocol.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:523)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at com.example.androidsample4.SANclass.getEventsFromAnXML(SANclass.java:115)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at com.example.androidsample4.SANclass$Mytask.doInBackground(SANclass.java:92)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at com.example.androidsample4.SANclass$1.onClick(SANclass.java:58)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.view.View.performClick(View.java:3131)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.view.View$PerformClick.run(View.java:12035)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.os.Handler.handleCallback(Handler.java:587)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.os.Handler.dispatchMessage(Handler.java:92)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.os.Looper.loop(Looper.java:132)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at android.app.ActivityThread.main(ActivityThread.java:4123)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at java.lang.reflect.Method.invokeNative(Native Method)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at java.lang.reflect.Method.invoke(Method.java:491)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:844)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
08-21 16:36:41.087 E/AndroidRuntime( 4076): at dalvik.system.NativeStart.main(Native Method)
08-21 16:36:41.092 V/AudioPolicyManager( 2713): releaseOutput() 1
08-21 16:36:41.092 W/ActivityManager( 2891):   Force finishing activity com.example.androidsample4/.SANclass

如果我包含“new Mytask.execute()”方法，我将强制关闭。这可能是什么原因？请指导我...

Answer 1

不要在后台线程中更新 UI。它应该在 onPostExecute()

中完成

Toast.makeText(getBaseContext(), "error:"+e.getMessage(), Toast.LENGTH_SHORT).show();
myXmlContent.setText(stringXmlContent);

在 onPostExecute() 中执行此步骤

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