Anwendung wird beendet bei .setText in onCreate?

package de.test.app; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 
import android.support.v7.app.ActionBarActivity; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.EditText; 
public class MainActivity extends ActionBarActivity { 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
if (savedInstanceState == null) { 
getSupportFragmentManager().beginTransaction() 
.add(R.id.container, new PlaceholderFragment()) 
.commit(); 
} 
EditText editText = (EditText) findViewById(R.id.editText); 
editText.setText("blabla"); 
} 


@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; 
} 
@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
// Handle action bar item clicks here. The action bar will 
// automatically handle clicks on the Home/Up button, so long 
// as you specify a parent activity in AndroidManifest.xml. 
int id = item.getItemId(); 
if (id == R.id.action_settings) { 
return true; 
} 
return super.onOptionsItemSelected(item); 
} 
/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 
public PlaceholderFragment() { 
} 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
Bundle savedInstanceState) { 
View rootView = inflater.inflate(R.layout.fragment_main, container, false); 
return rootView; 
} 
} 
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
android:paddingBottom="@dimen/activity_vertical_margin" 
tools:context="de.test.app.MainActivity$PlaceholderFragment"> 
<TextView 
android:text="@string/hello_world" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" 
android:id="@+id/textView" /> 
<EditText 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" 
android:inputType="textMultiLine" 
android:ems="10" 
android:id="@+id/editText" 
android:layout_below="@+id/textView" 
android:layout_alignParentLeft="true" 
android:layout_alignParentStart="true" 
android:layout_marginLeft="50dp" 
android:layout_marginTop="99dp" /> 
</RelativeLayout>