Using onPrepareOptionsMenu instead of onCreateOptionsMenu in Fragment

问题

I had a problem setting up some fragment menu items in the ActionBar and I found a way to solve it, but I don't understand why it worked.

I wanted to change the visibility in a menu item right after I inflated it from a menu xml file in onCreateOptionsMenu method. The code seems to work fine, but there's no visible effect. I solved the problem inflating the menu in onCreateOptionsMenu method but changing the visibility of it in onPrepareOptionsMenu method.

What I want to know is why changing the visibility in onCreateOptionsMenu does not work.

What can I do in onPrepareOptionsMenu that I can't do in onCreateOptionsMenu?

Is there any pattern to follow here?

Thanks!

Here's the relevant code, just in case:

public class MyFragment extends Fragment {

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);
        inflater.inflate(R.menu.my_menu, menu);

        // This does not work, compiles and runs fine, but has no visible effect
        MenuItem someMenuItem = menu.findItem(R.id.some_menu_item);
        someMenuItem.setVisible(false);
    }

    @Override
    public void onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);

        // This does work
        MenuItem someMenuItem = menu.findItem(R.id.some_menu_item);
        someMenuItem.setVisible(false);
    }
}

回答1:

You should call super.onCreateOptionsMenu(menu, inflater); after you have created your menu, not before. That sends the menu up in the hierarchy and other fragments or the activity may want to add items themselves.

The activity is responsible for the displaying and managing the menu, so if you change the visibility after it has been sent to the activity, nothing much is going to happen.

Now, when you call super.onPrepareOptionsMenu(menu); it will "prepare" it's menu, but it will now take the changes you've made in the onCreateOptionsMenu into account.

回答2:

May be the code should return true to make the menu visible, that means you should put return true; statement in both onCreateOptionsMenu() and onPrepareOptionsMenu().

Hope this helps.

回答3:

I use the onPrepareOptionsMenu to update which items on the menu should be active and which ones should be grayed out/removed depending on the current state of the activity. Use the setVisible method of the menu item to control whether it is currently shown on the menu or not.

回答4:

This works for me

public class ContentFragment extends android.support.v4.app.Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.content_frame,container,false);
    setHasOptionsMenu(true);
    return v;
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate(R.menu.note_menu,menu);
    super.onCreateOptionsMenu(menu, inflater);
}
}

Try it

来源：https://stackoverflow.com/questions/11375981/using-onprepareoptionsmenu-instead-of-oncreateoptionsmenu-in-fragment