ViewPager with WindowManager

Question

I use WindowManager to show the view on the screen pretty much like what Facebook Messenger does with ChatHeads. It works great for simple views, but I have a problem adding something like a viewpager. Can someone help me how to add ViewPager as a user interface using WindowManager.

Here is a sample code:

ViewPager viewPager = (ViewPager) mDialogView.findViewById(R.id.view_pager);
//returns a list of fragments
List<Fragment> fragments = getFragments();
mMyAdapter = new MyAdapter(*--GET FRAGMENT MANAGER--*, fragments);
viewPager.setAdapter(mMyAdapter);

The problem is how to get the fragment manager, because WindowManager is used from a service, not from an Activity

I completed the following tutorial: http://www.piwai.info/chatheads-basics/