Hide/Show Action Bar Option Menu Item for different fragments

I have a Sherlock Fragment Activity in which there are 3 Fragments.

Fragment A, Fragment B, Fragment C are three fragments. I want to show a done option menu in Fragment B only.

And the activity is started with Fragment A. When Fragment B is selected done button is added.

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    if(!menusInflated){
        inflater.inflate(R.menu.security, menu);
        menusInflated=true;
    }

    super.onCreateOptionsMenu(menu, inflater);
}

When I again start Fragment A I want to options Menu DONE (which was set at Fragment B) for this I am doing like this

setHasOptionsMenu(false);
MenuItem item = (MenuItem) menu.findItem(R.id.done_item);
item.setVisible(false);

But this is not hiding at all, also it is giving NullPointerException when Activity if first started with Fragment A.

Please let me know what is the problem.

This is one way of doing this:

add a "group" to your menu:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <group
        android:id="@+id/main_menu_group">
         <item android:id="@+id/done_item"
              android:title="..."
              android:icon="..."
              android:showAsAction="..."/>
    </group>
</menu>

then, add a

Menu menu;

variable to your activity and set it in your override of onCreateOptionsMenu:

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    this.menu = menu;
    // inflate your menu here
}

After, add and use this function to your activity when you'd like to show/hide the menu:

public void showOverflowMenu(boolean showMenu){
    if(menu == null)
        return;
    menu.setGroupVisible(R.id.main_menu_group, showMenu);
}

I am not saying this is the best/only way, but it works well for me.