https://stackoverflow.com/questions/46564984/android-custom-keyboard-preview-view-constrained-to-parent-layout/49725647#49725647

layoutAndShowPopupWindow.java

private void layoutAndShowPopupWindow(Key key, int xPosition) {
    popupWindow = new PopupWindow(popupView,
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    popupWindow.setClippingEnabled(false);// <-- let popup display above keyboard
    int location[] = new int[2];
    key.getLocationInWindow(location);
    int measureSpec = View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
    popupView.measure(measureSpec, measureSpec);
    int popupWidth = popupView.getMeasuredWidth();
    int spaceAboveKey = key.getHeight() / 4;
    int x = xPosition - popupWidth / popupView.getChildCount() / 2;
    int y = location[1] - popupView.getMeasuredHeight() - spaceAboveKey;
    popupWindow.showAtLocation(key, Gravity.NO_GRAVITY, x, y);

    // using popupWindow.showAsDropDown(key, 0, yOffset) might be
    // easier than popupWindow.showAtLocation() 
}