ListView in neuer Activity öffnen - Problem

package com.example.meineapp; 


import java.util.ArrayList; 
import java.util.List; 
import android.app.Activity; 
import android.os.Bundle; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.TextView; 
import android.widget.Toast; 


public class ObjektListActivity extends Activity{ 
     private List<Objekt>dieObjekte= new ArrayList<Objekt>(); 
     @Override 
     protected void onCreate(Bundle savedInstanceState){ 
          super.onCreate(savedInstanceState); 
          setContentView(R.layout.listview_layout); 
          populateObjektList(); 
          populateListView(); 
          registerClickCallback(); 
     } 


     private void populateObjektList(){ 
          dieObjekte.add(new Objekt("Objekt 1", R.drawable.ic_launcher)); 
          dieObjekte.add(new Objekt("Objekt 2", R.drawable.ic_launcher)); 
          dieObjekte.add(new Objekt("Objekt 3", R.drawable.ic_launcher)); 
          dieObjekte.add(new Objekt("Objekt 4", R.drawable.ic_launcher)); 
          dieObjekte.add(new Objekt("Objekt 5", R.drawable.ic_launcher)); 
     } 


//*******Wenn man den folgenden Teil auskommentiert gibt es keine Probleme********** 
     
     private void populateListView(){ 
          ArrayAdapter<Objekt>adapter = new MyListAdapter(); 
          ListView list=(ListView) findViewById(R.id.listView1); 
          list.setAdapter(adapter); 
     } 


     private class MyListAdapter extends ArrayAdapter<Objekt>{ 
          public MyListAdapter(){ 
               super(ObjektListActivity.this, R.layout.item_view, dieObjekte); 
          } 


          @Override 
          public View getView(int position, View ConvertView, ViewGroup parent){ 
               View itemView=ConvertView; 
               if (itemView==null){ 
                    itemView=getLayoutInflater().inflate(R.layout.item_view, parent, false); 
               } 


               Objekt currentObjekt= dieObjekte.get(position); 
               ImageView imageView = (ImageView) itemView.findViewById (R.id.item_icon); 
               imageView.setImageResource(currentObjekt.getIconID()); 
               TextView bezText = (TextView) itemView.findViewById (R.id.item_txtBezeichnung); 
               bezText.setText(currentObjekt.getBez()); 


               return itemView; 
          } 
     } 


     private void registerClickCallback(){ 
          ListView list=(ListView) findViewById(R.id.listView1); 
          list.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
               @Override 
               public void onItemClick(AdapterView<?> parent, View ViewClicked, int position, long id) { 
                    Objekt clickedObjekt=dieObjekte.get(position); 
                    String message="Position "+position+" Objektbezeichnung: "+ clickedObjekt.getBez(); 
                    Toast.makeText(ObjektListActivity.this, message, Toast.LENGTH_LONG).show(); 
               } 
          }); 
     } 


//*****************Ende des Teils***************************************** 


}

private void populateGridView(){ 
          GridView gridView = (GridView)findViewById(R.id.grid_view); 
          gridView.setAdapter(new ImageAdapter(this)); 
          gridView.setOnItemClickListener(new OnItemClickListener(){ 
                @Override 
                public void onItemClick(AdapterView<?> parent, View v, int position, long id){ 
                     if (position==0) { 
                           setContentView(R.layout.activity_main); 
                      } 
                      if (position==1) { 
                           setContentView(R.layout.activity_main); 
                           TextView titel = (TextView)findViewById(R.id.textView1); 
                           TextView text=(TextView)findViewById(R.id.textView2); 
                           titel.setText(getString(R.string.titel)); 
                           text.setText(getString(R.string.text)); 
                      } 
                      if (position==2){ 
                           startActivity(new Intent(MainActivity.this, TabActivityKarte.class)); 
                      } 
                      if (position==3){ 
                           startActivity(new Intent(MainActivity.this, TabActivitySteckbriefe.class)); 
                      } 
                      if (position==4){ 
                           startActivity(new Intent(MainActivity.this, ObjektListActivity.class)); 
                      } 
               } 
          }); 
      }

package com.example.meineapp; 
     public class Objekt { 
          private String bez; 
          private int iconID;


          public Objekt(String bez, int iconID){ 
               super(); 
               this.bez=bez; 
               this.iconID=iconID; 
          } 


          public String getBez(){ 
               return bez; 
          } 


          public int getIconID(){ 
               return iconID; 
          } 


     }

]<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
          android:layout_width="match_parent"
          android:layout_height="match_parent" > 


               <ImageView 
                         android:id="@+id/item_icon" 
                         android:layout_width="wrap_content" 
                         android:layout_height="wrap_content" 
                         android:layout_alignParentLeft="true" 
                         android:layout_alignParentTop="true" 
                         android:maxHeight="80dp" 
                         android:maxWidth="80dp" 
                         android:adjustViewBounds="true" 
                         android:src="@drawable/objekt1" /> 


              <TextView 
                        android:id="@+id/item_txtBezeichnung" 
                        android:layout_width="wrap_content" 
                        android:layout_height="wrap_content" 
                        android:layout_alignBottom="@+id/item_icon" 
                        android:layout_marginBottom="14dp" 
                        android:layout_marginLeft="16dp" 
                        android:layout_toRightOf="@+id/item_icon" 
                        android:text="@string/einleitungstitel" 
               /> 
</RelativeLayout> 






listview_layout.xml 


<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
          android:layout_width="match_parent" 
          android:layout_height="match_parent" 
          android:orientation="vertical" > 


               <ListView 
                         android:id="@+id/listView1" 
                         android:layout_width="match_parent" 
                         android:layout_height="wrap_content" 
                         android:layout_marginTop="15dp"/> 


</LinearLayout>