invalidateOptionsMenu 在片段中不起作用

显示或隐藏项目ActionBar根据文本中是否有文本EditText or not.

所以，我做了以下事情

public class NounSearch extends android.app.Fragment 
{
    EditText seachEditText;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        View rootView = inflater.inflate(R.layout.nounsearchactivity, container, false);

        // Intiate EditText
        seachEditText =(EditText) rootView.findViewById(R.id.nounSearch);
        seachEditText.setOnEditorActionListener(new TextView.OnEditorActionListener() {
            @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event)
            {
                if (actionId == EditorInfo.IME_ACTION_SEARCH) {
                    searchResult.Entities = new ArrayList<NounModel>();
                    _currentPage = 0;
                    categoryId = -1;
                    new GetNouns().execute();
                    return true;
                }
                
                
                return false;
            }
        });

        seachEditText.addTextChangedListener(new TextWatcher() {
            public void afterTextChanged(Editable s)
            {
                // ...
            }
        
            public void beforeTextChanged(CharSequence s, int start, int count, int after)
            {
                    // ...
            }
        
            public void onTextChanged(CharSequence s, int start, int before, int count)
            {
                getActivity().invalidateOptionsMenu();
            }
        });
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater)
    {
        super.onCreateOptionsMenu(menu, inflater);
        
        if (seachEditText.getText().toString().length() > 0){
            menu.findItem(R.id.action_search).setVisible(true);
        }
        else {
            menu.findItem(R.id.action_search).setVisible(false);
        }
    }
}

但是，那ActionItem永远不会出现。我怎样才能实现这个目标？

用于更新onCreateOptionsMenu在片段内你需要调用setHasOptionsMenu(true);在 - 的里面onCreate片段的方法。不然你打电话的时候是无法更新的 getActivity().invalidateOptionsMenu();

sample:

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

EDIT:

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater)
{
    if(seachEditText.getText().toString().length() > 0) {
        menu.findItem(R.id.action_search).setVisible(true);
    }
    else {
        menu.findItem(R.id.action_search).setVisible(false);
    }
    super.onCreateOptionsMenu(menu, inflater);
}