call a webservice

hi all can any one help me i am newer to android and java
i wont to call a webservice from android
my webservice code is
public class test : System.Web.Services.WebService {

public test () {

//Uncomment the following line if using designed components
//InitializeComponent();
}

[WebMethod]
public String GetStCourses(string prefixText)
{
PageController pc = new PageController();

string dt = pc.fill_Client(0);

return dt;
}

}

and i try to call it from android by using this code

import java.io.IOException;

import org.ksoap2.SoapEnvelope;
import org.ksoap2.SoapFault;
import org.ksoap2.serialization.PropertyInfo;
import org.ksoap2.serialization.SoapObject;
import org.ksoap2.serialization.SoapSerializationEnvelope;
import org.ksoap2.transport.AndroidHttpTransport;
import org.ksoap2.transport.HttpTransportSE;
import org.xmlpull.v1.XmlPullParserException;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.widget.TextView;

public class Mainz extends Activity {

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_mainz);
// WebServiceCallExample();
SoapObject request = new SoapObject("http://tempuri.org/", "GetStCourses");

//add parameters to web service method..
request.addProperty("prefixText", "1");

SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
envelope.dotNet = true;
envelope.setOutputSoapObject(request);

HttpTransportSE androidHttpTransport = new HttpTransportSE("http://localhost/test.asmx");
try {
androidHttpTransport.call("http://tempuri.org/GetStCourses", envelope);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

Object result = null;
try {
result = (Object) envelope.getResponse();
} catch (SoapFault e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

but when i run the app it give a message 'unfortunately the process has stopped'
can any one help me or tel me why?
thanks