How to check condition before moving to next page in viewpager

In my application i'm trying to implement small quiz using radio button and I'm trying to implement in viewpager and now my issue is that I have displayed question in viewpager and I trying to check condition before moving to next page and need to display toast message based on condition. however i'm getting error and app crashes. I have posted my code part below

t_vPager.setOnPageChangeListener(new OnPageChangeListener()
                {

                    @Override
                    public void onPageSelected(int position)
                    {
                        // TODO Auto-generated method stub
                        System.out.println("checking");

                            switch(position)
                    {
                        case 0:

                            System.out.println("question1 ");

                            id=radioanswergroup.getCheckedRadioButtonId();

                            radioanswerButton = (RadioButton)findViewById(id);

                            System.out.println("answer--"+radioanswerButton.getText());

                            break;

                        case 1:

                            System.out.println("question2 ");
                            break;

                        case 2:

                            System.out.println("question3 ");
                            break;

                        case 3:

                            System.out.println("question4 ");
                            break;
                    }

                                }
                        else 
                        {
                            System.out.println("verify the answer");
                        }

                    }

                    @Override
                    public void onPageScrolled(int arg0, float arg1, int arg2) 
                    {
                        // TODO Auto-generated method stub

                    }

                    @Override
                    public void onPageScrollStateChanged(int arg0)
                    {
                        // TODO Auto-generated method stub

                    }
                });

logcat error

    03-31 13:34:18.743: E/InputEventReceiver(11605): Exception dispatching input event.
03-31 13:34:18.743: E/MessageQueue-JNI(11605): Exception in MessageQueue callback: handleReceiveCallback
03-31 13:34:18.758: E/MessageQueue-JNI(11605): java.lang.NullPointerException
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at com.example.instantenglish.Todaytest$Dailytask$1.onPageSelected(Todaytest.java:234)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:567)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:551)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2015)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.View.dispatchTouchEvent(View.java:7350)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2412)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2147)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2139)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1476)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.app.Activity.dispatchTouchEvent(Activity.java:2487)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2087)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.View.dispatchPointerEvent(View.java:7535)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3415)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3347)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4456)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4434)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4538)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.os.MessageQueue.nativePollOnce(Native Method)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.os.MessageQueue.next(MessageQueue.java:125)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.os.Looper.loop(Looper.java:124)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at android.app.ActivityThread.main(ActivityThread.java:4921)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at java.lang.reflect.Method.invokeNative(Native Method)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at java.lang.reflect.Method.invoke(Method.java:511)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
03-31 13:34:18.758: E/MessageQueue-JNI(11605):  at dalvik.system.NativeStart.main(Native Method)
03-31 13:34:18.763: D/AndroidRuntime(11605): Shutting down VM
03-31 13:34:18.763: W/dalvikvm(11605): threadid=1: thread exiting with uncaught exception (group=0x41e0b2a0)
03-31 13:34:18.773: E/AndroidRuntime(11605): FATAL EXCEPTION: main
03-31 13:34:18.773: E/AndroidRuntime(11605): java.lang.NullPointerException
03-31 13:34:18.773: E/AndroidRuntime(11605):    at com.example.instantenglish.Todaytest$Dailytask$1.onPageSelected(Todaytest.java:234)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:567)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:551)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2015)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.View.dispatchTouchEvent(View.java:7350)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2412)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2147)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2418)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2161)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2139)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1476)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.app.Activity.dispatchTouchEvent(Activity.java:2487)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2087)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.View.dispatchPointerEvent(View.java:7535)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3415)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3347)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4456)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4434)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4538)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:171)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.os.MessageQueue.nativePollOnce(Native Method)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.os.MessageQueue.next(MessageQueue.java:125)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.os.Looper.loop(Looper.java:124)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at android.app.ActivityThread.main(ActivityThread.java:4921)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at java.lang.reflect.Method.invokeNative(Native Method)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at java.lang.reflect.Method.invoke(Method.java:511)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
03-31 13:34:18.773: E/AndroidRuntime(11605):    at dalvik.system.NativeStart.main(Native Method)

this is my full code

import java.util.ArrayList;
import java.util.Collections;

import org.json.JSONArray;
import org.json.JSONObject;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v4.view.ViewPager.OnPageChangeListener;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Switch;
import android.widget.Toast;
import android.widget.RadioGroup.OnCheckedChangeListener;
import android.widget.TextView;

public class Todaytest extends Activity implements OnClickListener
{

    //urls

            String url="link";

            //json array

            JSONArray jarray;

            //Array list

            ArrayList<String> tst_alquestion = new ArrayList<String>();

            ArrayList<String> tst_alcorrectanswer = new ArrayList<String>();

            ArrayList<String> tst_alwronganswer1 = new ArrayList<String>();

            ArrayList<String> tst_alwronganswer2 = new ArrayList<String>();

            ArrayList<String> tst_alwronganswer3 = new ArrayList<String>();

            ArrayList<String> tst_alwronganswer4 = new ArrayList<String>();

            ArrayList<String> shufanswer=new ArrayList<String>();

            //Radio button

            RadioGroup radioanswergroup;

            RadioButton radioanswerButton,btn1,btn2,btn3,btn4;

            int id,qid=0;

            //text view

            TextView question;

            ViewPager t_vPager;

            PagerAdapter t_padapter;


        @Override
        protected void onCreate(Bundle savedInstanceState)
        {
            // TODO Auto-generated method stub
            super.onCreate(savedInstanceState);

            setContentView(R.layout.test);

            t_vPager = (ViewPager) findViewById(R.id.ttpager);

            question=(TextView)findViewById(R.id.qst);

            radioanswergroup=(RadioGroup)findViewById(R.id.radioanswer);

            btn1=(RadioButton)findViewById(R.id.btn1);

            btn2=(RadioButton)findViewById(R.id.btn2);

            btn3=(RadioButton)findViewById(R.id.btn3);

            btn4=(RadioButton)findViewById(R.id.btn4);

            new Dailytask().execute();

            //questionview();


        }



        @Override
        public void onClick(View v) 
        {
            // TODO Auto-generated method stub



        }



        private class Dailytask extends AsyncTask<String, String, JSONObject> 
        {
            private ProgressDialog pDialog;

            @Override
            protected void onPreExecute() 
            {
                super.onPreExecute();



                pDialog = new ProgressDialog(Todaytest.this);

                pDialog.setMessage("Loading Assessment ...");

                pDialog.setIndeterminate(false);

                pDialog.setCancelable(true);

                pDialog.show();
            }

            @Override
            protected JSONObject doInBackground(String... args) 
            {
                Json j = new Json();
                // Getting JSON from URL
                JSONObject json = j.getJSONFromUrl(url);
                return json;
            }

            @Override
            protected void onPostExecute(JSONObject json)
            {

                System.out.println("---------------return today test json------------"+json);

                pDialog.dismiss();

                try
                {
                        // Getting JSON Array from URL
                    JSONObject jobj = json.getJSONObject("response");

                    jarray = jobj.getJSONArray("Test");

                    System.out.println("json array length"+jarray.length());

                    for (int i = 0; i < jarray.length(); i++) 
                    {
                        JSONObject data = jarray.getJSONObject(i);
                        // Storing JSON item in a Variable
                        tst_alquestion.add(data.getString("question"));

                        tst_alcorrectanswer.add(data.getString("correctanswer"));

                        tst_alwronganswer1.add(data.getString("wronganswer1"));

                        tst_alwronganswer2.add(data.getString("wronganswer2"));

                        tst_alwronganswer3.add(data.getString("wronganswer3"));

                        tst_alwronganswer4.add(data.getString("wronganswer4"));

                        System.out.println("correct answer------------>"+tst_alcorrectanswer);
                        System.out.println("wroang ans1------------>"+tst_alwronganswer1);

                        System.out.println("wroang ans2------------>"+tst_alwronganswer2);
                        System.out.println("wroang ans3------------>"+tst_alwronganswer3);
                        System.out.println("wroang ans4------------>"+tst_alwronganswer4);



                    }


                }
                catch(Exception e)
                {

                }

    t_padapter = new testadapter(Todaytest.this, tst_alquestion,tst_alcorrectanswer ,tst_alwronganswer1,tst_alwronganswer2,tst_alwronganswer3,tst_alwronganswer4);


                t_vPager.setAdapter(t_padapter);

                t_vPager.setOnPageChangeListener(new OnPageChangeListener()
                {

                    @Override
                    public void onPageSelected(int position)
                    {
                        // TODO Auto-generated method stub
                        System.out.println("checking"+position);
                        //Toast.makeText(getApplicationContext(), "please answer for above questions",Toast.LENGTH_SHORT ).show();

                        switch(position)
                        {
                            case 0:

                                System.out.println("question1 ");

                                id=radioanswergroup.getCheckedRadioButtonId();

                                radioanswerButton = (RadioButton)findViewById(id);

                                System.out.println("answer--"+radioanswerButton.getText());

                                break;

                            case 1:

                                System.out.println("question2 ");
                                break;

                            case 2:

                                System.out.println("question3 ");
                                break;

                            case 3:

                                System.out.println("question4 ");
                                break;
                        }




                    }

                    @Override
                    public void onPageScrolled(int arg0, float arg1, int arg2) 
                    {
                        // TODO Auto-generated method stub

                    }

                    @Override
                    public void onPageScrollStateChanged(int arg0)
                    {
                        // TODO Auto-generated method stub

                    }
                });


            }
        }



}

test.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:background="#F5DA81" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="15dp"
        android:background="#FFFFFF"
        android:orientation="vertical" >

    <android.support.v4.view.ViewPager
        android:id="@+id/ttpager"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    </LinearLayout>
</LinearLayout>

//testadapter

package com.example.instantenglish;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;

import org.apache.http.util.ByteArrayBuffer;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Parcelable;
import android.os.StrictMode;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.RelativeLayout;
import android.widget.TextView;

public class testadapter extends PagerAdapter
{
    // Declare Variables
    Context context;
    ArrayList<String> question;
    ArrayList<String> answer;
    ArrayList<String> ans1;
    ArrayList<String> ans2;
    ArrayList<String> ans3;
    ArrayList<String> ans4;

    int[] flag;
    LayoutInflater inflater;


    public testadapter(Todaytest tt, ArrayList<String> tst_alquestion,
            ArrayList<String> tst_alcorrectanswer,
            ArrayList<String> tst_alwronganswer1,
            ArrayList<String> tst_alwronganswer2,
            ArrayList<String> tst_alwronganswer3,
            ArrayList<String> tst_alwronganswer4) 
    {
        // TODO Auto-generated constructor stub
        this.context=tt;
        this.question=tst_alquestion;
        this.answer=tst_alcorrectanswer;
        this.ans1=tst_alwronganswer1;
        this.ans2=tst_alwronganswer2;
        this.ans3=tst_alwronganswer3;
        this.ans4=tst_alwronganswer4;
    }

        @Override
    public int getCount() {
        return question.size();
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == ((LinearLayout) object);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position)
    {

        // Declare Variables
        TextView txtquestion;
        RadioButton radioanswerButton,btn1,btn2,btn3,btn4,btn5;        //TextView txtpopulation;
        RadioGroup radioanswergroup;   

        inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View itemView = inflater.inflate(R.layout.todaytest, container,
                false);

        // Locate the TextViews in viewpager_item.xml
        txtquestion = (TextView) itemView.findViewById(R.id.qst);
        radioanswergroup=(RadioGroup)itemView.findViewById(R.id.radioanswer);

        btn1=(RadioButton)itemView.findViewById(R.id.btn1);

        btn2=(RadioButton)itemView.findViewById(R.id.btn2);

        btn3=(RadioButton)itemView.findViewById(R.id.btn3);

        btn4=(RadioButton)itemView.findViewById(R.id.btn4);

        btn5=(RadioButton)itemView.findViewById(R.id.btn5);


        // Capture position and set to the TextViews
        txtquestion.setText(question.get(position));
        btn1.setText(answer.get(position));
        btn2.setText(ans1.get(position));
        btn3.setText(ans2.get(position));
        btn4.setText(ans3.get(position));
        btn5.setText(ans4.get(position));
        //txtpopulation.setText(population[position]);

        // Locate the ImageView in viewpager_item.xml

        // Add viewpager_item.xml to ViewPager
        ((ViewPager) container).addView(itemView);

        return itemView;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        // Remove viewpager_item.xml from ViewPager
        ((ViewPager) container).removeView((LinearLayout) object);

    }

    @Override
    public void restoreState(Parcelable arg0, ClassLoader arg1) {
        // TODO Auto-generated method stub

    }

    @Override
    public Parcelable saveState() {
            // TODO Auto-generated method stub
            return null;
    }

    @Override
    public void startUpdate(View arg0) {
            // TODO Auto-generated method stub

    }   

  }

testadapter 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" 
     android:background="#F5DA81">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:background="#FFFFFF" >

        <TextView
            android:id="@+id/qst"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:layout_gravity="center"
            android:layout_marginTop="20dp"
            android:background="@drawable/txtview"
            android:gravity="center"
            android:text="Questions"
            android:textColor="#000000"
            android:textStyle="bold" />

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="25dp"
            android:layout_marginRight="25dp"
            android:layout_marginTop="25dp" >

                <RadioGroup
                    android:id="@+id/radioanswer"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content" >


                <RadioButton
                    android:id="@+id/btn1"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:text="@string/rbtn1" 
                    android:textColor="#000000"/>

                <RadioButton
                    android:id="@+id/btn2"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="15dp"
                    android:text="@string/rbtn2"
                    android:textColor="#000000" />

                <RadioButton
                    android:id="@+id/btn3"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="15dp"
                    android:text="@string/rbtn3"
                    android:textColor="#000000" />

                  <RadioButton
                      android:id="@+id/btn4"
                      android:layout_width="wrap_content"
                      android:layout_height="wrap_content"
                      android:layout_marginTop="15dp"
                      android:text="@string/rbtn4"
                      android:textColor="#000000" />

                  <RadioButton
                      android:id="@+id/btn5"
                      android:layout_width="wrap_content"
                      android:layout_height="wrap_content"
                      android:layout_marginTop="15dp"
                      android:text="@string/rbtn5"
                      android:textColor="#000000" />

                 </RadioGroup>



        </TableRow>

    </LinearLayout>

</LinearLayout>

Answers


As your details show you are using getCheckedRadioButtonId() but in your xml there is non of RadioButton is checked. so just checked a RedioButton like below

<RadioButton
       android:id="@+id/btn3"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_marginTop="15dp"
       android:text="@string/rbtn3"
       android:checked="true"
       android:textColor="#000000" />

and also use a condition before getting button with checked id. use like below

int id=radioanswergroup.getCheckedRadioButtonId();
if(id>0)  
radioanswerButton = (RadioButton)findViewById(id); 

You get a nullPointerException cause you're trying to find your RadioGroup radioanswergroup from text.xml using findViewById.

At this point (in onCreate), your ViewPager isn't instantiated since you'll do it in a AsyncTask. That's why your radioanswergroup is null, and it's the same for the following variables: question, btn1, btn2, btn3 & btn4.

Hope this helped.


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