Prevent printing from finishing activity.

        public PrintDocumentAdapterDelegate(Activity activity,

                PrintDocumentAdapter documentAdapter) {

            if (activity.isFinishing()) {

                // The activity is already dead hence the onActivityDestroyed callback won't be

                // triggered. Hence it is not save to print in this situation.

                throw new IllegalStateException("Cannot start printing for finishing activity");

            }

            mActivity = activity;

            mDocumentAdapter = documentAdapter;

            mHandler = new MyHandler(mActivity.getMainLooper());