小贝子编程

Android AsyncTask Xml Pull Parsing



我正在制作一个应用程序，获得一些XML并解析它，使对象的数组列表传递给另一个活动。这都是在AsyncTask中完成的。当我运行应用程序时，它立即崩溃，我很难找出问题出在哪里。非常感谢任何帮助。

Main Activity 

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;
import java.util.ArrayList;
import org.xmlpull.v1.XmlPullParserException;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.app.ProgressDialog;
import android.util.Log;
import android.view.Menu;
import android.widget.TextView;
public class MainActivity extends Activity {
ProgressDialog progressDialog;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    new QuizWorker().execute("http://liisp.uncc.edu/~mshehab/api/trivia.xml");
}
@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;
}


// START QuizWorker Class
public class QuizWorker extends AsyncTask<String, Void, ArrayList<Question>> {
    @Override
    protected ArrayList<Question> doInBackground(String... params) {
        String urlString = params[0];
        try {
            URL url = new URL(urlString);
            HttpURLConnection con = (HttpURLConnection) url.openConnection();
            con.setRequestMethod("GET");
            con.connect();
            int statusCode = con.getResponseCode();
            if(statusCode == HttpURLConnection.HTTP_OK) {
                InputStream in = con.getInputStream();
                return QuestionUtil.parseQuestions(in);
            }
        }
        catch (MalformedURLException e) {
            e.printStackTrace();
        }
        catch (ProtocolException e) {
            e.printStackTrace();
        }
        catch (IOException e) {
            e.printStackTrace();
        }
        catch (XmlPullParserException e) {
            e.printStackTrace();
        }
        return null;
    }
    @Override
    protected void onPostExecute(ArrayList<Question> result) {
        super.onPostExecute(result);
        progressDialog.dismiss();
        TextView tv = (TextView) findViewById(R.id.ready_status);
        tv.setText("Trivia Ready");
        // testing purposes
        Log.d("demo", result.toString());
    }
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        progressDialog = new ProgressDialog(MainActivity.this);
        progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        progressDialog.setCancelable(false);
        progressDialog.setMessage("Loading Trivia");
        progressDialog.show();
    }


} // END Class
} // END Activity

正如你所看到的，我有MainActivity在这里与AsyncTask。AsyncTask调用另一个类QuestionUtil 

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
public class QuestionUtil {
static ArrayList<Question> parseQuestions(InputStream xmlIn) throws XmlPullParserException, IOException {
    XmlPullParser parser = XmlPullParserFactory.newInstance().newPullParser();
    parser.setInput(xmlIn, "UTF-8");
    Question question = null;
    ArrayList<Question> questionList = new ArrayList<Question>();
    Choices choices = null;
    ArrayList<Choices> choiceList = new ArrayList<Choices>();
    int event = parser.getEventType();
    while (event != XmlPullParser.END_DOCUMENT) {
        switch (event) {
        case XmlPullParser.START_TAG:
            if(parser.getName().equals("question")) {
                question = new Question();
                try {
                    question.setId(parser.getAttributeValue(null, "id"));
                }
                catch (NumberFormatException ex) { }
            }
            else if (parser.getName().equals("text")) {
                question.setText(parser.nextText());
            }
            else if (parser.getName().equals("image")) {
                question.setImage(parser.nextText());
            }
            else if (parser.getName().equals("choices")) {
                boolean isCorrect;
                String answer;
                parser.next();
                while (parser.getName().equals("choice")) {
                    if (parser.getAttributeValue(null, "answer") != null) {
                        isCorrect = true;
                        answer = parser.nextText();
                        choices = new Choices(isCorrect, answer);
                    }
                    else {
                        isCorrect = false;
                        answer = parser.nextText();
                        choices = new Choices(isCorrect, answer);
                    }
                    choiceList.add(choices);
                    parser.next();
                }
                question.setChoices(choiceList);
            } // END Choices Parsing
            break;
        case XmlPullParser.END_TAG:
            if (parser.getName().equals("question")) {
                questionList.add(question);
                question = null;
            }
            break;
        default:
            break;
        } // END Switch
        event = parser.next();
    } // END While loop
    return questionList;
}
}

这个类使用PULL解析出XML，并使我的Question类的对象的数组列表:

import java.util.ArrayList;
import android.os.Parcel;
import android.os.Parcelable;
public class Question implements Parcelable {

public String id;
public String text;
public String image;
public ArrayList<Choices> choices;

public Question() {
    // TODO Auto-generated constructor stub
}

// Constructs a Question from values
public Question (String id, String text, String image, ArrayList<Choices> choices) {
    this.id = id;
    this.text = text;
    this.image = image;
    this.choices = choices;
}

public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}

public String getText() {
    return text;
}
public void setText(String text) {
    this.text = text;
}

public String getImage() {
    return image;
}
public void setImage(String image) {
    this.image = image;
}

public ArrayList<Choices> getChoices() {
    return choices;
}
public void setChoices(ArrayList<Choices> choices) {
    this.choices = choices;
}
@Override
public String toString() {
    return "Question [id=" + id + ", text=" + text + ", image=" + image
            + "]";
}

/**
 * Constructs a Question from a Parcel
 * @param parcel Source Parcel
 */
public Question (Parcel parcel) {
    this.id = parcel.readString();
    this.text = parcel.readString();
    this.image = parcel.readString();
    this.choices = parcel.readArrayList(null);
}
@Override
public int describeContents() {
    return 0;
}
// Required method to write to Parcel
@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(id);
    dest.writeString(text);
    dest.writeString(image);
    dest.writeList(choices);
}
// Method to recreate a Question from a Parcel
public static Creator<Question> CREATOR = new Creator<Question>() {
    @Override
    public Question createFromParcel(Parcel source) {
        return new Question(source);
    }
    @Override
    public Question[] newArray(int size) {
        return new Question[size];
    }
};

}

我也有一个叫做Choices的类，我把答案，然后我做一个数组列表，我添加到每个问题对象。

当我运行代码时，应用程序甚至没有启动，只是立即说它停止工作了。日志说它在doInBackground中。

Log/Errors 

03-17 15:52:51.509: D/dalvikvm(2032): GC_FOR_ALLOC freed 93K, 5% free 3020K/3168K, paused 2ms, total 4ms
03-17 15:52:51.509: I/dalvikvm-heap(2032): Grow heap (frag case) to 3.607MB for 635808-byte allocation
03-17 15:52:51.529: D/dalvikvm(2032): GC_FOR_ALLOC freed 5K, 5% free 3635K/3792K, paused 13ms, total 13ms
03-17 15:52:51.589: D/(2032): HostConnection::get() New Host Connection established 0xb8e93af0, tid 2032
03-17 15:52:51.629: W/EGL_emulation(2032): eglSurfaceAttrib not implemented
03-17 15:52:51.629: D/OpenGLRenderer(2032): Enabling debug mode 0
03-17 15:52:51.679: W/EGL_emulation(2032): eglSurfaceAttrib not implemented
03-17 15:52:51.799: W/dalvikvm(2032): threadid=11: thread exiting with uncaught exception (group=0xb2cbdb20)
03-17 15:52:51.799: E/AndroidRuntime(2032): FATAL EXCEPTION: AsyncTask #1
03-17 15:52:51.799: E/AndroidRuntime(2032): Process: com.example.midterm, PID: 2032
03-17 15:52:51.799: E/AndroidRuntime(2032): java.lang.RuntimeException: An error occured while executing doInBackground()
03-17 15:52:51.799: E/AndroidRuntime(2032):     at android.os.AsyncTask$3.done(AsyncTask.java:300)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.util.concurrent.FutureTask.run(FutureTask.java:242)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.lang.Thread.run(Thread.java:841)
03-17 15:52:51.799: E/AndroidRuntime(2032): Caused by: java.lang.NullPointerException
03-17 15:52:51.799: E/AndroidRuntime(2032):     at com.example.midterm.QuestionUtil.parseQuestions(QuestionUtil.java:54)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at com.example.midterm.MainActivity$QuizWorker.doInBackground(MainActivity.java:60)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at com.example.midterm.MainActivity$QuizWorker.doInBackground(MainActivity.java:1)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at android.os.AsyncTask$2.call(AsyncTask.java:288)
03-17 15:52:51.799: E/AndroidRuntime(2032):     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
03-17 15:52:51.799: E/AndroidRuntime(2032):     ... 4 more
03-17 15:52:52.169: E/WindowManager(2032): android.view.WindowLeaked: Activity com.example.midterm.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b2faf408 V.E..... R......D 0,0-456,144} that was originally added here
03-17 15:52:52.169: E/WindowManager(2032):  at android.view.ViewRootImpl.<init>(ViewRootImpl.java:348)
03-17 15:52:52.169: E/WindowManager(2032):  at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:248)
03-17 15:52:52.169: E/WindowManager(2032):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.Dialog.show(Dialog.java:286)
03-17 15:52:52.169: E/WindowManager(2032):  at com.example.midterm.MainActivity$QuizWorker.onPreExecute(MainActivity.java:101)
03-17 15:52:52.169: E/WindowManager(2032):  at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:587)
03-17 15:52:52.169: E/WindowManager(2032):  at android.os.AsyncTask.execute(AsyncTask.java:535)
03-17 15:52:52.169: E/WindowManager(2032):  at com.example.midterm.MainActivity.onCreate(MainActivity.java:28)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.Activity.performCreate(Activity.java:5231)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
03-17 15:52:52.169: E/WindowManager(2032):  at android.os.Handler.dispatchMessage(Handler.java:102)
03-17 15:52:52.169: E/WindowManager(2032):  at android.os.Looper.loop(Looper.java:136)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.ActivityThread.main(ActivityThread.java:5017)
03-17 15:52:52.169: E/WindowManager(2032):  at java.lang.reflect.Method.invokeNative(Native Method)
03-17 15:52:52.169: E/WindowManager(2032):  at java.lang.reflect.Method.invoke(Method.java:515)
03-17 15:52:52.169: E/WindowManager(2032):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-17 15:52:52.169: E/WindowManager(2032):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
03-17 15:52:52.169: E/WindowManager(2032):  at dalvik.system.NativeStart.main(Native Method)

任何帮助都将非常感激。我的代码中没有错误，我只是不知道什么可能是错误的，为什么它甚至没有开始。

关于日志的这一部分:

03-17 15:52:52.169: E/WindowManager(2032): android.view.WindowLeaked: Activity com.example.midterm.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{b2faf408 V.E..... R......D 0,0-456,144} that was originally added here
03-17 15:52:52.169: E/WindowManager(2032):  at android.view.ViewRootImpl.<init>(ViewRootImpl.java:348)
03-17 15:52:52.169: E/WindowManager(2032):  at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:248)
03-17 15:52:52.169: E/WindowManager(2032):  at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
03-17 15:52:52.169: E/WindowManager(2032):  at android.app.Dialog.show(Dialog.java:286)

我建议你看看这个链接。我想只要另一个错误不再发生，这个就可以工作了。

下面一行表示存在一个NullPointerException。要确定什么是空，有必要知道QuestionUtil.java:54是哪一行。

03-17 15:52:51.799: E/AndroidRuntime(2032):     at com.example.midterm.QuestionUtil.parseQuestions(QuestionUtil.java:54)

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