ok, so i follow uhmdown's answer for dimming background activity when pop window is open. But it creates problem for me. it was dimming activity and include popup window (means dimmed-black layered on both activity and popup also, it can not be separate them).
so i tried this way,
create an dimming_black.xml file for dimming effect,
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
android:shape="rectangle">
<solid android:color="#33000000" />
</shape>
And add as background in FrameLayout as root xml tag, also put my other controls in LinearLayout like this layout.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="@drawable/ff_drawable_black">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
android:layout_gravity="bottom"
android:background="@color/white">
// other codes...
</LinearLayout>
</FrameLayout>
at last i show popup on my MainActivity with some extra parameter set as below.
//instantiate popup window
popupWindow = new PopupWindow(viewPopup, LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT, true);
//display the popup window
popupWindow.showAtLocation(layout_ff, Gravity.BOTTOM, 0, 0);
Result:

it works for me, also solved problem as commented by BaDo. With this Actionbar also can be dimmed.
P.s i am not saying uhmdown's is wrong. i learnt form his answer and try to evolve for my problem. I also confused whether this is a good way or not.
Any suggestions is also appreciated also sorry for my bad English.