AlertDialog Box is not working if there is no internet connection
<p>I am doing a google map project. My requirement is if I press a button in the present activity, it will take to google map activity else it should show the alert dialog showing the network not available message. The app crashes if there is no network. The Following is the code:</p>

<pre><code>public class HomeFragment extends Fragment {
          protected static final Context Context = null;

    // flag for Internet connection status
    Boolean isInternetPresent = false;

    // Connection detector class
    ConnectionDetector cd;      public HomeFragment(){}

        ImageButton button;         @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_home, container, false);

        return rootView;
    }

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

        // creating connection detector class instance
        cd = new ConnectionDetector( getActivity());


        button = (ImageButton) getActivity().findViewById(R.id.button);
                button.setOnClickListener(new OnClickListener() {
                        @Override           public void onClick(View v) {
                // TODO Auto-generated method stub


                // get Internet status
                isInternetPresent = cd.isConnectingToInternet();


                // check for Internet status
                if (isInternetPresent) {
                    // Internet Connection is Present
                    // make HTTP requests

                    Intent i = new Intent(getActivity(), GoogleActivity.class);
                    startActivity(i);       


                } else {
                    // Internet connection is not present
                    // Ask user to connect to Internet

                    showAlertDialog(Context ,  "No Internet Connection" ,  "You don't have internet connection.", true);

                }

                        }       });


            }
         public void showAlertDialog(Context HomeFragment, String title, String message, Boolean status) {
            AlertDialog alertDialog = new AlertDialog.Builder(HomeFragment).create();

            // Setting Dialog Title
            alertDialog.setTitle(title);

            // Setting Dialog Message
            alertDialog.setMessage(message);

            // Setting alert dialog icon
            alertDialog.setIcon((status) ? R.drawable.success : R.drawable.fail);

            // Setting OK Button
            alertDialog.setButton(DialogInterface.BUTTON_NEGATIVE,
                    "OK", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {

                        }
                    });

            // Showing Alert Message
            alertDialog.show();
        }   }
</code></pre>

<p>Logcat</p>

<pre><code>01-06 16:22:48.940: W/dalvikvm(4223): threadid=1: thread exiting with uncaught exception (group=0x40de4540)
01-06 16:22:48.960: E/AndroidRuntime(4223): FATAL EXCEPTION: main
01-06 16:22:48.960: E/AndroidRuntime(4223): java.lang.NullPointerException
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:142)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.app.AlertDialog$Builder.&lt;init&gt;(AlertDialog.java:359)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at com.ons.bhoomi.HomeFragment.showAlertDialog(HomeFragment.java:90)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at com.ons.bhoomi.HomeFragment$1.onClick(HomeFragment.java:77)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.view.View.performClick(View.java:4102)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.view.View$PerformClick.run(View.java:17085)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.os.Handler.handleCallback(Handler.java:615)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.os.Looper.loop(Looper.java:155)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at android.app.ActivityThread.main(ActivityThread.java:5520)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at java.lang.reflect.Method.invokeNative(Native Method)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at java.lang.reflect.Method.invoke(Method.java:511)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1058)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:825)
01-06 16:22:48.960: E/AndroidRuntime(4223):     at dalvik.system.NativeStart.main(Native Method)
</code></pre>