Question

我正在关注developers.facebook.com上的教程，用于实现登录和注销功能。应用程序正常工作直到登录。如果我尝试添加注销功能，它会抛出一个Null指针Exception.Code完全取自facebook。请发布。看看代码

 public class MainActivity extends FragmentActivity {


private static final int SETTINGS = 2;
private MenuItem settings;

private static final String TAG = "SelectionFragment";
private static final int SPLASH = 0;
private static final int SELECTION = 1;
private static final int FRAGMENT_COUNT = SETTINGS +1;;

private Fragment[] fragments = new Fragment[FRAGMENT_COUNT];
private boolean isResumed = false;
private UiLifecycleHelper uiHelper;


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

    setContentView(R.layout.activity_main);

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

    FragmentManager fm = getSupportFragmentManager();
    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();
}

@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 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();
}

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
            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
        showFragment(SELECTION, false);
    } else {
        // otherwise present the splash screen
        // and ask the person to login.
        showFragment(SPLASH, false);
    }
}

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


@Override
public boolean onPrepareOptionsMenu(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;
}


   }

Logcat错误是http://tinypic.com/r/30bh0n7/8 http://tinypic.com/r/n2itcj/8

Answer 1

你没有设置

fragments[SPLASH]

Android Project Null Pointer异常

1 个答案: