this.getWindow().getDecorView().findViewById(android.R.id.content)
or
this.findViewById(android.R.id.content)
or
this.findViewById(android.R.id.content).getRootView()
this.getWindow().getDecorView().findViewById(android.R.id.content)
or
this.findViewById(android.R.id.content)
or
this.findViewById(android.R.id.content).getRootView()