Android : How to display an alert dialog (with ok button) when an image button is clicked?

I want to display an AlertDialog when an image_button is clicked. The AlertDialog will show a message with a "OK" button. The dialog needs to be dismissed when OK is clicked. I have tried the following code and it throws an exception. Please tell me what am I doing wrong here.

public void showHelp(View view)
{
    AlertDialog.Builder builder = new AlertDialog.Builder(getApplicationContext());
    builder.setPositiveButton("helpMessafe", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                  dialog.dismiss();
               }
           });
    AlertDialog alert = builder.create();
    alert.show();
}

XML for the corresponding button is

<ImageButton
    android:id="@+id/popupbutton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/textView3"
    android:layout_below="@+id/textView2"
    android:layout_marginTop="18dp"
    android:layout_toLeftOf="@+id/towing1"
    android:layout_toRightOf="@+id/textView1"
    android:contentDescription="@string/help_me_choose"
    android:onClick="showHelp"
    android:src="@drawable/help_icon" />

Error generated

08-15 06:49:37.834: E/AndroidRuntime(1898): FATAL EXCEPTION: main 08-15 06:49:37.834: E/AndroidRuntime(1898): java.lang.IllegalStateException: Could not execute method of the activity 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.View$1.onClick(View.java:3599) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.View.performClick(View.java:4204) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.View$PerformClick.run(View.java:17355) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.os.Handler.handleCallback(Handler.java:725) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.os.Handler.dispatchMessage(Handler.java:92) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.os.Looper.loop(Looper.java:137) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.app.ActivityThread.main(ActivityThread.java:5041) 08-15 06:49:37.834: E/AndroidRuntime(1898): at java.lang.reflect.Method.invokeNative(Native Method) 08-15 06:49:37.834: E/AndroidRuntime(1898): at java.lang.reflect.Method.invoke(Method.java:511) 08-15 06:49:37.834: E/AndroidRuntime(1898): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 08-15 06:49:37.834: E/AndroidRuntime(1898): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 08-15 06:49:37.834: E/AndroidRuntime(1898): at dalvik.system.NativeStart.main(Native Method) 08-15 06:49:37.834: E/AndroidRuntime(1898): Caused by: java.lang.reflect.InvocationTargetException 08-15 06:49:37.834: E/AndroidRuntime(1898): at java.lang.reflect.Method.invokeNative(Native Method) 08-15 06:49:37.834: E/AndroidRuntime(1898): at java.lang.reflect.Method.invoke(Method.java:511) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.View$1.onClick(View.java:3594) 08-15 06:49:37.834: E/AndroidRuntime(1898): ... 11 more 08-15 06:49:37.834: E/AndroidRuntime(1898): Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.ViewRootImpl.setView(ViewRootImpl.java:571) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:246) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69) 08-15 06:49:37.834: E/AndroidRuntime(1898): at android.app.Dialog.show(Dialog.java:281) 08-15 06:49:37.834: E/AndroidRuntime(1898): at com.sri.myapp.GetInfo.showHelp(GetInfo.java:163)