android file download

Question

Hallo guys, im here in austria how are you doing?

i have startet developing android and writing my own small app that gets files from a server to display the information in a ListView. I really spent a day to look after the best and easiest way to get files from a server. However i wrote the program and tested it - and now i have a serious error message when running the virtual htc machine.

Its called: The application org.me.newspuler (process org.me.newspuler) has stopped unexpectedly. Please try again.

Under this message is put a "Force Close" Button.

I really dont know how to get a hint to the problem, NewsPuler is my APP, - i think I need help from some more proffs

I have 2 classes - one for the download file(i think here is the mistake) - one for the Main Activity When the compiler comes to the point in the code where the instance from "DownloadFile" is created... the error appears.

the download file class:

package logik;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author raa
 */
public class DownloadFile {
    InputStream is = null;
    String link = null;
    BufferedReader d = null;
    URL url = null;
    String s;
    ArrayList<String> al = new ArrayList<String>();


    public  DownloadFile(String link) throws MalformedURLException{
        this.link = link;
        url = new URL(link);

        try {
            is = url.openStream();
        } catch (IOException ex) {
            Logger.getLogger(DownloadFile.class.getName()).log(Level.SEVERE, null, ex);
        }

        d = new BufferedReader(new InputStreamReader(is));
        try {
            while ((s = d.readLine()) != null) {
                al.add(s);
            }
        } catch (IOException ex) {
            Logger.getLogger(DownloadFile.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public ArrayList getArrayList(){
        return al;
    }
}

And here (it works correclty if you leave the commented code, but when you uncomment it - not)

package org.me.newspuler;

import logik.DownloadFile;
import android.app.Activity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;



/**
 *
 * @author raa
 */
public class MainActivity extends Activity {
    ArrayList<String> al;
     DownloadFile df;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        ListView myListView = (ListView)findViewById(R.id.myListView);
//        try {
//            df = new DownloadFile("http://www.google.at/");
//
//        } catch (MalformedURLException ex) {
//            Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
//        }

            //        al.add("Test");
            //         final ArrayAdapter<String> aa = new ArrayAdapter<String>(this,
            //                android.R.layout.simple_list_item_1, al);
            //
            //         myListView.setAdapter(aa);


    }

}

I would be really glad to get some help! Kindly Regards from Austria.

Answer 1

looks to me like your trying to call

al.add("Test");

when al is null. That would definitely crash the app.

change the declaration of al to

ArrayList<String> al = new ArrayList<String>();

there could be other issues but thats the one which really sticks out to me.

i recommend using android logcat to get specific information about the error.

I use eclipse and plugins for development.

a tutorial is here.

http://d.android.com/guide/developing/eclipse-adt.html

having proper debugging will help you allot.

---

in response to what you said try this.

public class Tester extends Activity {

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    ArrayList<String> list = null;
    try {
        list = DownloadFile("http://www.google.com");
    } catch (Exception e) {
        Log.i("File Download Test", e.getLocalizedMessage(), e);
    }
    if (list != null)
        for (String s : list)
            Log.i("File Download Test", s);
}

public ArrayList<String> DownloadFile(String link) throws ClientProtocolException, IOException, URISyntaxException {
    ArrayList<String> al = new ArrayList<String>();
    HttpClient httpclient = new DefaultHttpClient();
    HttpGet httpget = new HttpGet(new URI(link));
    HttpResponse response = httpclient.execute(httpget);
    HttpEntity entity = response.getEntity();
    InputStream is = null;
    try {
        is = entity.getContent();
    } catch (IOException ex) {
        Log.i("", ex.getMessage(), ex);
    }
    BufferedReader d = new BufferedReader(new InputStreamReader(is));
    String s = null;
    try {
        while ((s = d.readLine()) != null) {
            al.add(s);
        }
    } catch (IOException ex) {
        Log.i("", ex.getMessage(), ex);
    }
    return al;
}

}

and make sure your manifest includes the internet permission

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.tester"
  android:versionCode="1"
  android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".Tester"
              android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>
<uses-permission
    android:name="android.permission.INTERNET"></uses-permission>

Answer 2

Do NOT use the java logging classes import java.util.logging.Logger;. Use the android logcat class.

Answer 3

i have tested the code now in one class - seems that there is a problem with the openStream. i got a UnknownHostException when i testet only the URL snipped.