progress dialog with asynctask

Question

i have 3 classes and the class called WebServiceCleint class is extending Asynctask and in doInBackgrnd() i m passing url and i m getting data from webservice. but i m calling this from another class's method called VerifyTeacherId. Now how can i show progress dialog??? where should i write the pg.show and pg.dismiss.???

public  class WebServiceClient extends AsyncTask<String, Void, String>
{

 private static final String base_path = "http://www.gdaschools.in/";
 protected static final String SLASH = "/";


 private ProgressDialog dialog;
 private Activity activity;

 public WebServiceClient(Activity activity) {
        this.activity = activity;
        this.dialog = new ProgressDialog(activity);
    }

    @Override
     protected void onPreExecute() {
            this.dialog.setMessage("Progress start");
            this.dialog.show();
        }



@Override
protected String doInBackground(String... params) {

    StringBuffer sb = new StringBuffer();
    sb.append(base_path);
    sb.append(params[0]);
    HttpRetriever retrieveResponse = new HttpRetriever();
    retrieveResponse.retrieve(sb.toString());
    return retrieveResponse.getResponseXml();
}



 @Override
protected void onPostExecute(String result) {
     if (this.dialog.isShowing()) {
           this.dialog.dismiss();
     }
}
}

And the method where i m calling is it in another class named SelectOptionActivity. The method is

public void verifyTeacherId(View view)
{
    teacherIdString = TeacherId.getText().toString().trim();

    clientThread = new WebServiceClient(SelectOptionActivity.this);
    clientThread.execute("teacher/" + teacherIdString);     

    try 
    {
        String xml = clientThread.get();

        DocumentBuilderFactory factory1 = DocumentBuilderFactory.newInstance();
        factory1.setNamespaceAware(true);
        try
        {
            DocumentBuilder builder = factory1.newDocumentBuilder();
            Document doc =builder.parse(new InputSource(new StringReader(xml))); 
            Element root = doc.getDocumentElement();
            if (doc != null) 
            {
                    NodeList nl = doc.getElementsByTagName("empId");
                    if (nl.getLength() > 0)
                    {
                        Node node = nl.item(0);
                        responseTeacherId = node.getTextContent();
                    }
                    NodeList n2=doc.getElementsByTagName("empName");
                    if (n2.getLength() > 0)
                    {
                        Node node = n2.item(0);
                        responseTeacherName = node.getTextContent();

                    }
            }

             Toast.makeText(getBaseContext(),""+responseTeacherId,10).show();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ExecutionException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 

Now getting error like

05-08 12:10:10.834: D/AndroidRuntime(524): Shutting down VM
05-08 12:10:10.834: W/dalvikvm(524): threadid=1: thread exiting with uncaught exception (group=0x40014760)
05-08 12:10:10.872: E/AndroidRuntime(524): FATAL EXCEPTION: main
05-08 12:10:10.872: E/AndroidRuntime(524): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.GDAProj/com.GDAProj.SelectOptionActivity}: java.lang.NullPointerException
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1739)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1831)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ActivityThread.access$500(ActivityThread.java:122)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1024)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.os.Looper.loop(Looper.java:132)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ActivityThread.main(ActivityThread.java:4123)
05-08 12:10:10.872: E/AndroidRuntime(524):  at java.lang.reflect.Method.invokeNative(Native Method)
05-08 12:10:10.872: E/AndroidRuntime(524):  at java.lang.reflect.Method.invoke(Method.java:491)
05-08 12:10:10.872: E/AndroidRuntime(524):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
05-08 12:10:10.872: E/AndroidRuntime(524):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
05-08 12:10:10.872: E/AndroidRuntime(524):  at dalvik.system.NativeStart.main(Native Method)
05-08 12:10:10.872: E/AndroidRuntime(524): Caused by: java.lang.NullPointerException
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:132)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:65)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:120)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.AlertDialog.<init>(AlertDialog.java:80)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ProgressDialog.<init>(ProgressDialog.java:76)
05-08 12:10:10.872: E/AndroidRuntime(524):  at com.GDAProj.WebServiceClient.<init>(WebServiceClient.java:20)
05-08 12:10:10.872: E/AndroidRuntime(524):  at com.GDAProj.SelectOptionActivity.<init>(SelectOptionActivity.java:70)
05-08 12:10:10.872: E/AndroidRuntime(524):  at java.lang.Class.newInstanceImpl(Native Method)
05-08 12:10:10.872: E/AndroidRuntime(524):  at java.lang.Class.newInstance(Class.java:1301)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.Instrumentation.newActivity(Instrumentation.java:1022)
05-08 12:10:10.872: E/AndroidRuntime(524):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1730)
05-08 12:10:10.872: E/AndroidRuntime(524):  ... 11 more

Answer 1

Pass context of your current activity to AsyncTask class and using that context show progress dialog in onPreExecute() and dismiss it onPostExecute()

public  class WebServiceClient extends AsyncTask<String, Void, String>
{
 private static final String base_path = "http://www.gdaschools.in";
 protected static final String SLASH = "/";
 private ProgressDialog dialog;
 private Activity activity;

public WebServiceClient(Activity activity) {
    this.activity = activity;
    this.dialog = new ProgressDialog(activity);
}

@Override
 protected void onPreExecute() {
        this.dialog.setMessage("Progress start");
        this.dialog.show();
    }

@Override
    protected void onPostExecute(final Boolean success) {
        if (this.dialog.isShowing()) {
           this.dialog.dismiss();
        }

.
.
.

Code is only for your understanding..

Answer 2

The instance of Activity is null because you are creating object of WebServiceClient before oncreate function. While passing Activity or Context be sure that Activity have created other wise it null will be passed and you will get this error