how to access UI elements in parent activity from fragment

Question

parent activity layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     tools:context=".LockerCodeActivity" >      <LinearLayout         android:id="@+id/fragment_container"         android:layout_width="match_parent"         android:layout_height="match_parent">     </LinearLayout>      <ProgressBar         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_centerHorizontal="true"         android:layout_centerVertical="true"         android:id="@+id/ctrlActivityIndicator"         android:indeterminateOnly="true"         android:keepScreenOn="false"      />      <TextView         android:id="@+id/tv_results"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_centerHorizontal="true"         android:layout_centerVertical="true"         android:text="" />  </RelativeLayout> 

Inflate the fragment in the parent activity onCreate function

FragmentManager fragmentManager = getFragmentManager();     FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();     Fragment scannerFragment = new ScanFragment();     fragmentTransaction.add(R.id.fragment_container, scannerFragment);     fragmentTransaction.commit(); 

Working great so far... now how do I hide the progressbar? This is what I've tried

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {     View view = inflater.inflate(R.layout.fragment_scan, container, false);      ProgressBar progressBar = (ProgressBar) view.findViewById(R.id.ctrlActivityIndicator);     progressBar.setVisibility(View.INVISIBLE);     return view;     } 

I get a null pointer exception

Answer 1

Since you want the Activity's views, you're going to want to do this:

ProgressBar progressBar = (ProgressBar) getActivity().findViewById(R.id.ctrlActivityIndicator); 

You call getActivity() to get the Activity instance then you use findViewById() as normal (provided that R.id.ctrlActivityIndicator is part of the Activity layout, you won't get NPEs).