Null Zeiger Ausnahme auf Set Adapter Android

Question

Ich habe versucht, ein Problem für ein paar Stunden jetzt zu lösen, aber ich habe es versäumt, es herauszufinden. Ich habe die Daten aus einer Online-XML-Datei über eine Async-Task abgerufen und den Basisadapter aufgerufen, um die Daten in einer Listenansicht zu füllen. Wenn ich den Adapter jedoch auf die Listenansicht einstelle, gibt es einen Null Pointer Exception-Fehler, und ich kann nicht herausfinden, welches Objekt tatsächlich Null ist. Jede Hilfe wäre willkommen, danke!

MainActivity

package com.example.sandeshpoudel.lab13; 
import android.os.Bundle; 
     import android.support.v7.app.AppCompatActivity; 
     import android.util.Log; 
     import android.view.View; 
     import android.widget.Adapter; 
     import android.widget.Button; 
     import android.widget.EditText; 
     import android.widget.ListAdapter; 
     import android.widget.ListView; 
     import java.util.ArrayList; 
    import java.util.List; 
    public class MainActivity extends AppCompatActivity { 
    private Button get_xml; 
    private EditText Url_input; 
    public final static String TAG = "my-filter"; 
    private ListAdapter newAdapter; 

    private ListView list_player; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     get_xml = (Button)findViewById(R.id.xml_button); 
     Url_input = (EditText) findViewById(R.id.url_input); 
     list_player = (ListView) findViewById(R.id.list_player); 
     get_xml.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 

       new Fetch_Xml().execute(Url_input.getText().toString()); 
       Log.i(TAG,"fetching xml data from Url "+Url_input.getText().toString()); 


      } 
     }); 


    } 
    public void getList(List<Player>players){ 
    newAdapter =new AdapterExample(this,players); 
    list_player.setAdapter(newAdapter); 


    } 

} 

Adapter Klasse

package com.example.sandeshpoudel.lab13; 
import android.app.Activity; 
import android.content.Context; 
import android.inputmethodservice.Keyboard; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.BaseAdapter; 
import android.widget.ListAdapter; 
import android.widget.TextView; 

import java.util.List; 

public class AdapterExample extends BaseAdapter { 
private Context context; 
private List<Player> playerList; 
private LayoutInflater myInflatter; 
public AdapterExample(Context context,List<Player>myList){ 
    super(); 
    this.context = context; 
    this.playerList= myList; 
    Log.i(MainActivity.TAG,"created new adapter"); 
} 
@Override 
public int getCount() { 
    return playerList.size(); 
} 

@Override 
public Object getItem(int position) { 
    return playerList.get(position); 
} 

@Override 
public long getItemId(int position) { 

    return 0; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
Player myPlayer = (Player) getItem(position); 
    Log.i(MainActivity.TAG,"inflattering the layout"); 
     myInflatter = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE); 
     View Row = myInflatter.inflate(R.layout.players_list, parent, false); 
     TextView name = (TextView) Row.findViewById(R.id.nameHere); 
     TextView id = (TextView) Row.findViewById(R.id.idHere); 
     name.setText(myPlayer.getName()); 
     name.setText(myPlayer.getId()); 
    Log.i(MainActivity.TAG,"positioned name: "+myPlayer.getName()+". id: "+myPlayer.getId().toString()+"\n"); 




    return Row; 
} 
} 

content_main.xml

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout  xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
app:layout_behavior="@string/appbar_scrolling_view_behavior" 
tools:context="com.example.sandeshpoudel.lab13.MainActivity" 
android:id="@+id/Url_input"> 

<Button 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="GET XML" 
    android:id="@+id/xml_button" 
    android:layout_below="@+id/url_input" 
    android:layout_centerHorizontal="true" /> 

<EditText 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/url_input" 
    android:layout_alignParentTop="true" 
    android:layout_centerHorizontal="true" 
    android:text="http://users.metropolia.fi/~peterh/players.xml" /> 

<ListView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/list_player" 
    android:layout_below="@+id/xml_button" /> 

players_list.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout  xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
app:layout_behavior="@string/appbar_scrolling_view_behavior" 
tools:context="com.example.sandeshpoudel.lab13.MainActivity" 
android:id="@+id/Url_input" 
android:orientation="horizontal" 
android:background="#99ccff"> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_weight="2" 
    android:inputType="number" 

    android:textSize="20sp" 
    android:id="@+id/idHere"/> 
<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_weight="4" 
    android:inputType="textPersonName" 

    android:textSize="20sp" 
    android:id="@+id/nameHere"/> 

Fehlerprotokoll:

<!-- 04-12 12:01:18.196 25131-25131/? E/AndroidRuntime: FATAL EXCEPTION:    main 
               Process: com.example.sandeshpoudel.lab13, PID: 25131 
               java.lang.NullPointerException 
                at com.example.sandeshpoudel.lab13.MainActivity.getList(MainActivity.java:45) 
                at com.example.sandeshpoudel.lab13.Fetch_Xml.onPostExecute(Fetch_Xml.java:51) 
                at com.example.sandeshpoudel.lab13.Fetch_Xml.onPostExecute(Fetch_Xml.java:20) 
                at android.os.AsyncTask.finish(AsyncTask.java:632) 
                at android.os.AsyncTask.access$600(AsyncTask.java:177) 
                at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645) 
                at android.os.Handler.dispatchMessage(Handler.java:102) 
                at android.os.Looper.loop(Looper.java:146) 
                at android.app.ActivityThread.main(ActivityThread.java:5694) 
                at java.lang.reflect.Method.invokeNative(Native Method) 
                at java.lang.reflect.Method.invoke(Method.java:515) 
                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291) 

com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1107) bei dalvik.system.NativeStart.main (native Methode) ->

Fetch_Xml

package com.example.sandeshpoudel.lab13; 
import android.os.AsyncTask; 
import android.util.Log; 
import org.xmlpull.v1.XmlPullParserException; 
import java.io.IOException; 
import java.io.InputStream; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 
import java.nio.charset.MalformedInputException; 
import java.util.ArrayList; 
import java.util.List; 


public class Fetch_Xml extends AsyncTask<String,Void,List<Player>> { 
private static final String TAG ="my-filter"; 
List<Player> newPlayerList; 

@Override 
protected List<Player> doInBackground(String ... params) { 
    String url = params[0]; 
    InputStream inputStream = null; 
    newPlayerList = null; 
    try { 
     inputStream = convertUrl(url.toString()); 
     newPlayerList = new ArrayList<>(new Xml_parser().parse(inputStream)); 
    }catch (MalformedURLException i){ 
     Log.i(TAG,"Error: "+i.toString()); 

    }catch (IOException i){ 
     Log.i(TAG,"Error: "+i.toString()); 
    } catch (XmlPullParserException e) { 
     Log.i(TAG,"Error: "+e.toString()); 
    } 

    for(Player P:newPlayerList){ 
     Log.i(TAG,"______________________\n Player Name: "+P.getName()+"\t Id "+P.getId()+"\n"); 
    } 
    return newPlayerList; 

} 

@Override 
protected void onPostExecute(List<Player>players) { 

new MainActivity().getList(players); 


} 

private InputStream convertUrl(String s) throws MalformedURLException,IOException { 
    URL url = new URL(s); 
    HttpURLConnection myConnection = (HttpURLConnection) url.openConnection(); 
    myConnection.setRequestMethod("GET"); 
    myConnection.setReadTimeout(10000); 
    myConnection.setConnectTimeout(10000); 
    myConnection.setDoInput(true); 
    myConnection.connect(); 
    Log.i(TAG,"coverted url to Input Stream"); 
    return myConnection.getInputStream(); 
} 
} 

Answer 1

in der MainActivity Sie haben eine Methode public void getList(List<Player>players){

dort ist die Initialisierung des Objekts AdapterExample genannt ...

Sie nie sind diese Methode aufrufen ...

Answer 2

Es scheint, dass Sie rufen die Methode getList nicht auf.

Dann könnten Sie List<Player> players = new ArrayList<>; Nullzeiger-Ausnahme zu vermeiden.

Ein Vorschlag, versuchen Sie, Ihren Code zu formatieren, ein gutes Format ist sehr wichtig.