onPrepareOptionsMenu 未被调用，MenuItem 未显示

Question

我有三个 fragments：R.id.splashFragment、R.id.selectionFragment 和 R.id.userSettingsFragment

我有一个 MenuItem 叫做 settings

我希望应用如何工作：

splashFragment为主画面。

然后当我点击splashFragment中的Login Button时，屏幕显示selectionFragment和MenuItem。

最后，当我点击 MenuItem 时，屏幕被重定向到 userSettingsFragment。

问题：

当我点击 Login Button 时，屏幕成功显示 selectionFragment。但是，MenuItem 没有显示，因此我也看不到 userSettingsFragment。

为了显示 MenuItem，我覆盖了 onPrepareOptionsMenu 方法。然而，在调试之后，我注意到 onPrepareOptionsMenu 永远不会被调用，因此 MenuItem 永远不会被显示。

谁能解释一下为什么 onPrepareOptionsMenu 从来没有被调用过？或者为什么 MenuItem 没有显示在屏幕上并可能提供解决方案？

谢谢。

EDITED CODE 包含更多片段代码 已编辑代码 现在包括所有代码

代码：

public class MainActivity extends FragmentActivity  {

    private static final int SPLASH = 0;
    private static final int SELECTION = 1;
    private static final int SETTINGS = 2;
    private static final int FRAGMENT_COUNT = SETTINGS +1;

    private MenuItem settings;

    private Fragment[] fragments = new Fragment[FRAGMENT_COUNT];

    private boolean isResumed = false;

    private UiLifecycleHelper uiHelper;
    private Session.StatusCallback callback = 
        new Session.StatusCallback() {
        @Override
        public void call(Session session, 
                SessionState state, Exception exception) {
            onSessionStateChange(session, state, exception);
        }
    };

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // only add the menu when the selection fragment is showing
        if (fragments[SELECTION].isVisible()) {
            if (menu.size() == 0) {
                settings = menu.add(R.string.settings);
            }
            return true;
        } else {
            menu.clear();
            settings = null;
        }
        return false;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (item.equals(settings)) {
            showFragment(SETTINGS, true);
            return true;
        }
        return false;
    }

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

        uiHelper = new UiLifecycleHelper(this, callback);
        uiHelper.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        FragmentManager fm = getSupportFragmentManager();
        fragments[SPLASH] = fm.findFragmentById(R.id.splashFragment);
        fragments[SELECTION] = fm.findFragmentById(R.id.selectionFragment);
        fragments[SETTINGS] = fm.findFragmentById(R.id.userSettingsFragment);

        FragmentTransaction transaction = fm.beginTransaction();
        for(int i = 0; i < fragments.length; i++) {
            transaction.hide(fragments[i]);
        }
        transaction.commit();
    }

    private void showFragment(int fragmentIndex, boolean addToBackStack) {
        FragmentManager fm = getSupportFragmentManager();
        FragmentTransaction transaction = fm.beginTransaction();
        for (int i = 0; i < fragments.length; i++) {
            if (i == fragmentIndex) {
                transaction.show(fragments[i]);

            } else {
                transaction.hide(fragments[i]);
            }
        }
        if (addToBackStack) {
            transaction.addToBackStack(null);
        }
        transaction.commit();
    }   

    @Override
    public void onResume() {
        super.onResume();
        uiHelper.onResume();
        isResumed = true;
    }

    @Override
    public void onPause() {
        super.onPause();
        uiHelper.onPause();
        isResumed = false;
    }

    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        uiHelper.onActivityResult(requestCode, resultCode, data);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        uiHelper.onDestroy();
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        uiHelper.onSaveInstanceState(outState);
    }
    private void onSessionStateChange(Session session, SessionState state, Exception exception) {
        // Only make changes if the activity is visible
        if (isResumed) {
            FragmentManager manager = getSupportFragmentManager();
            // Get the number of entries in the back stack
            int backStackSize = manager.getBackStackEntryCount();
            // Clear the back stack
            for (int i = 0; i < backStackSize; i++) {
                manager.popBackStack();
            }
            if (state.isOpened()) {
                // If the session state is open:
                // Show the authenticated fragment
                //              invalidateOptionsMenu();  ???
                showFragment(SELECTION, false);

            } else if (state.isClosed()) {
                // If the session state is closed:
                // Show the login fragment
                showFragment(SPLASH, false);
            }
        }
    }

    @Override
    protected void onResumeFragments() {
        super.onResumeFragments();
        Session session = Session.getActiveSession();

        if (session != null && session.isOpened()) {
            // if the session is already open,
            // try to show the selection fragment
            //          invalidateOptionsMenu();  ???
            showFragment(SELECTION, false);
        } else {
            // otherwise present the splash screen
            // and ask the person to login.
            showFragment(SPLASH, false);
        }
    }
}

Answer 1

我对此很陌生。 onPrepareOptionsMenu() 可能没问题——我还没有查过。但是，在我的 FragmentActivity 中，我使用的是 onCreateOptionsMenu():

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu

    getMenuInflater().inflate(R.menu.menu_page_view, menu);
    return true;
}

Answer 2

切换到 SelectionFragment 时，您必须调用 invalidateOptionsMenu()。这会强制系统刷新操作项，从而召回 onPrepareOptionsMenu() .

从Fragment代码中，你得先得到你activity：getActivity().invalidateOptionsMenu();

onPrepareOptionsMenu 未被调用，MenuItem 未显示

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