XML : How to make visible a layout programatically in fragment which is called in parent activity

I have a layout defined in fragment.xml which is called in activity.... and I want to make it visible when a button in parent activity action bar is pressed which is in onOptionsItemSelected() .when i do this it make a error of null object reference....

fragment.xml

          <RelativeLayout          android:visibility="invisible"          android:id="@+id/relative_layout_current_job"          android:layout_marginTop="5dp"          android:layout_marginBottom="5dp"          android:layout_marginLeft="5dp"          android:layout_marginRight="5dp"          android:layout_width="match_parent"          android:layout_height="wrap_content">          <TextView              android:id="@+id/text_view_current_job"              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:text="@string/text_current_job"              android:layout_centerHorizontal="true"              />          </RelativeLayout>    

mainActivity.java

      protected void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.activity_passenger_main);    }    @Override  public boolean onCreateOptionsMenu(Menu menu) {      if (!mNavigationDrawerFragment.isDrawerOpen()) {          // Only show items in the action bar relevant to this screen          // if the drawer is not showing. Otherwise, let the drawer          // decide what to show in the action bar.          getMenuInflater().inflate(R.menu.passenger_main, menu);          restoreActionBar();          return true;      }      return super.onCreateOptionsMenu(menu);  }    @Override  public boolean onOptionsItemSelected(MenuItem item) {      // Handle action bar item clicks here. The action bar will      // automatically handle clicks on the Home/Up button, so long      // as you specify a parent activity in AndroidManifest.xml.      int id = item.getItemId();        //noinspection SimplifiableIfStatement      if (id == R.id.action_job_confirm) {          Button b = (Button) findViewById(R.id.action_job_confirm);          RelativeLayout layoutCurrentJob=(RelativeLayout) findViewById(R.id.relative_layout_current_job);          TextView status = (TextView) findViewById(R.id.text_view_current_job_status_in_history);          if((b.getText().toString()) == "job confirm") {              status.setVisibility(View.INVISIBLE);              b.setText("Job Started");              layoutCurrentJob.setVisibility(View.VISIBLE);          }          else{              status.setVisibility(View.VISIBLE);              b.setText("jon confirm");              layoutCurrentJob.setVisibility(View.INVISIBLE);          }        }        return super.onOptionsItemSelected(item);  }    

mainmanu.xml

      <item android:id="@+id/action_job_confirm" android:title="job confirm"      app:showAsAction="never"/>