Android-使用viewPager更新其他片段中的textview

Question

i am trying to update a textview in fragment 3 from fragment it, but it returns me nullpointerexception. But when i update fragment 2 (listview) from fragment 1 it works perfectly. I wondering what is the problem, can anyone please guide me? Thanks.

my fragment 2 code where im trying to update my fragment 3:

public void onResume() {
    super.onResume();

    if (getListView() != null) {
        updateData();
        String tagName = "android:switcher:" + R.id.pager + ":" + 2;
        Bill f3 = (Bill)getActivity().getSupportFragmentManager().findFragmentByTag(tagName);
        f3.updateData2();
    }
}

my fragment 3 code to receive update:

void updateData2() {
    EventController controller = new EventController(getActivity());
    Intent objIntent = getActivity().getIntent();
    String eventId = objIntent.getStringExtra("eventId");   
    total = (TextView) getActivity().findViewById(R.id.displaytotal);
    total.setText(controller.getTotal(eventId));
}

my viewpager code:

public class DashboardActivity2 extends FragmentActivity implements TabListener{

private ViewPager viewPager;
private TabsPagerAdapter2 mAdapter;
private ActionBar actionBar;
// Tab titles
    private String[] tabs = { "Participant", "Expense","Bill" };

    @SuppressLint("NewApi")
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager = (ViewPager) findViewById(R.id.pager);
        actionBar = getActionBar();
        mAdapter = new TabsPagerAdapter2(getSupportFragmentManager());

        viewPager.setAdapter(mAdapter);
        actionBar.setHomeButtonEnabled(false);
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        // Adding Tabs
        for (String tab_name : tabs) {
            actionBar.addTab(actionBar.newTab().setText(tab_name)
                    .setTabListener(this));
        }

        /**
         * on swiping the viewpager make respective tab selected
         * */
        viewPager
                .setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

                    @Override
                    public void onPageSelected(int position) {
                        // on changing the page
                        // make respected tab selected
                        actionBar.setSelectedNavigationItem(position);
                    }

                    @Override
                    public void onPageScrolled(int arg0, float arg1,
                            int arg2) {
                    }

                    @Override
                    public void onPageScrollStateChanged(int arg0) {
                    }
                });
    }

    @Override
    public void onTabReselected(Tab arg0, FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onTabSelected(Tab arg0, FragmentTransaction arg1) {
        // TODO Auto-generated method stub
        // on tab selected
        // show respected fragment view
        viewPager.setCurrentItem(arg0.getPosition());
    }

    @Override
    public void onTabUnselected(Tab arg0, FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }
  }

This is my LogCat :

11-16 05:46:08.912: E/AndroidRuntime(17241): FATAL EXCEPTION: main
11-16 05:46:08.912: E/AndroidRuntime(17241): java.lang.NullPointerException
11-16 05:46:08.912: E/AndroidRuntime(17241):    at com.example.hapshare.Expense.onResume(Expense.java:109)
11-16 05:46:08.912: E/AndroidRuntime(17241):    at android.support.v4.app.Fragment.performResume(Fragment.java:1521)
11-16 05:46:08.912: E/AndroidRuntime(17241):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:963)
11-16 05:46:08.912: E/AndroidRuntime(17241):    at android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:823)
11-16 05:46:08.912: E/AndroidRuntime(17241):    at android.support.v4.app.FragmentManagerImpl.startPendingDeferredFragments(FragmentManager.java:1128)

Answer 1

The only thing I can think of is that the Fragment could become detached from the Activity when not visible. So, in updateData2() you should avoid doing anything that requires the Activity (like getActivity()). Save the data and don't do anything with it until you get to the onResume() method.

BTW, I found out that onAttach() is called before onCreate(). So, you could do anything that requires the Activity in onCreate(), onCreateView(), or onStart() as well as onResume().