Get screen width and height in a Fragment

This will give you what you want without needing for context or view:

import android.content.res.Resources;

int width = Resources.getSystem().getDisplayMetrics().widthPixels;

int height = Resources.getSystem().getDisplayMetrics().heightPixels;

This code also works with Fragments:

int width = getResources().getConfiguration().screenWidthDp;
int height = getResources().getConfiguration().screenHeightDp;

For comparing orientation:

if(getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE){...}

Try below modifed code of yours

DisplayMetrics displaymetrics = new DisplayMetrics();
getActivity().getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
int height = displaymetrics.heightPixels;
int width = displaymetrics.widthPixels;

or

Display display = getActivity().getWindowManager().getDefaultDisplay(); 
int stageWidth = display.getWidth();
int stageHeight = display.getHeight();

Basically you just required to put getActivity() (to get the context) before getWindowManager() function.