public class About extends Fragment {

    Intent intent;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.about, container, false);

        intent = new Intent(getActivity(), Contact_Developer.class);
        final Button button = (Button) rootView.findViewById(R.id.btnContactDev);

        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                startActivity(intent);
            }
        });

        return rootView;
    }

    @Override
        public void onActivityCreated (Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

            ((MyActivity) this.getActivity()).onFragmentReady();
        } 
}  

public class MyActivity extends FragmentActivity {
    private void onFragmentReady() {
        Log.i(TAG, "testing");
         intent = new Intent(getActivity(), Contact_Developer.class);
         final Button button = (Button) rootView.findViewById(R.id.btnContactDev);

        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                startActivity(intent);
            }
        });
    }

    public class About extends Fragment {
        ...
    }
}

OR


public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
  View rootView = inflater.inflate(R.layout.fragment_newcomplain, container, false);
    intent = new Intent(getActivity(), AddComplainActivity.class);
    final Button button = (Button) rootView.findViewById(R.id.btnAgreeComplain);

    button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            startActivity(intent);
        }
    });


    // Inflate the layout for this fragment    return rootView;

}