Android - 无法更新其他片段中的textview

Question

我正在尝试更新片段3中的textview，使用supportfragmentmanager从片段2更新，我的片段1和片段2可以完美地通信，但是当从片段3更新时，我得到nullpointerexception错误。有人可以指导我吗？感谢。

我的片段2代码，我试图更新我的片段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();
    }
}

我的片段3代码接收更新：

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));
}

我的viewpager代码：

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

    }

}

这是我的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

public class TabFragmentAdapter extends FragmentPagerAdapter {
public static final int INDEX_USER = 0;
public static final int INDEX_LOCAL_FILE = 1;
public static final int INDEX_INBOX = 2;
//
private final SparseArray<Class<? extends Fragment>> fragmentClz = new SparseArray<Class<? extends Fragment>>();
{
    fragmentClz.put(INDEX_USER, UserFragment.class);
    fragmentClz.put(INDEX_LOCAL_FILE, LocalFilesFragment.class);
    fragmentClz.put(INDEX_INBOX, InboxFragment.class);
}
private FragmentManager fragmentManager;

public TabFragmentAdapter(FragmentManager fm) {
    super(fm);
    fragmentManager = fm;
}

@Override
public Fragment getItem(int arg0) {
    Class<? extends Fragment> fc = fragmentClz.get(arg0);
    Fragment f = null;
    try {
        f = fc.newInstance();
    } catch (InstantiationException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
    return f;
}

/**
 * @param index
 *            {@link #INDEX_INBOX #INDEX_LOCAL_FILE ...}
 * @return
 */
public Fragment findFragment(int index) {
    if (recorder == null) {
        return null;
    }
    return fragmentManager.findFragmentByTag(recorder.get(index));
}

public Fragment findFragment(Class<? extends Fragment> fc) {
    return findFragment(0);
}

@Override
public int getCount() {
    return fragmentClz.size();
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Object object = super.instantiateItem(container, position);
    if (object instanceof Fragment) {
        Fragment f = (Fragment) object;
        if (recorder == null) {
            recorder = new SparseArray<String>();
        }
        recorder.put(position, f.getTag());
    }
    return object;
}

private SparseArray<String> recorder;

@Override
public Parcelable saveState() {
    return new FragmentIdRecorder(recorder);
}

@Override
public void restoreState(Parcelable state, ClassLoader loader) {
    if (state instanceof FragmentIdRecorder) {
        FragmentIdRecorder fir = (FragmentIdRecorder) state;
        recorder = fir.getRecorder();
    }
}

public static class FragmentIdRecorder implements Parcelable {
    private SparseArray<String> recorder;

    public SparseArray<String> getRecorder() {
        return recorder;
    }

    public FragmentIdRecorder(SparseArray<String> recorder) {
        this.recorder = recorder;
    }

    public FragmentIdRecorder(Parcel in) {
        recorder = new SparseArray<String>();
        int size = in.readInt();
        if (size <= 0) {
            return;
        }
        for (int i = 0; i < size; i++) {
            recorder.put(in.readInt(), in.readString());
        }
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        if (recorder == null || recorder.size() <= 0) {
            dest.writeInt(0);
            return;
        } else {
            int size = recorder.size();
            dest.writeInt(size);
            for (int i = 0; i < size; i++) {
                dest.writeInt(recorder.keyAt(i));
                dest.writeString(recorder.valueAt(i));
            }
        }
    }

    public static final Parcelable.Creator<FragmentIdRecorder> CREATOR = new Parcelable.Creator<FragmentIdRecorder>() {
        public FragmentIdRecorder createFromParcel(Parcel in) {
            return new FragmentIdRecorder(in);
        }

        public FragmentIdRecorder[] newArray(int size) {
            return new FragmentIdRecorder[size];
        }
    };
}

}

使用TabFramentAdapter.findFrament（），不要使用FramentManager获取frament by tag，因为标签是由FragmentPagerAdapter创建的，我认为不是安全性（其他版本可能会更改，哈哈）