Java 调用片段'；将适配器从其活动中删除

我已经创建了一个具有4个不同内容的片段的ViewPager。每个碎片的按钮上都有一个按钮条。当我点击其中一个按钮时，当前片段的数据应该被更新。因此，我在活动中实现了一些回调方法。但不幸的是，每次调用方法reloadArticleListFragment（），例如，当我单击按钮栏中的一个按钮时，我都会得到一个NullPointerException。我猜当前片段没有附加到活动，但我不知道为什么。你有什么建议吗

谢谢你的帮助

MainActivity.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener, DataFragment.Callbacks {

...

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // setup ui and instantiate some variables (missing in the example)

    mDataFragment = (AbstractDataFragment) mPagerAdapter.getItem(mViewPager.getCurrentItem());
    mAdapter = mDataFragment.getAdapter();
    rssService.execute(RssService.BLOG_URL);

    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    sharedPreferences.registerOnSharedPreferenceChangeListener(new SharedPreferences.OnSharedPreferenceChangeListener() {
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            if (key.equalsIgnoreCase("feedScope")) {
                mPagerAdapter.setFeedScope(Integer.parseInt(sharedPreferences.getString(key, "0")));
                reloadArticleListFragment();
            } else if (key.equalsIgnoreCase("countySelection")) {
                reloadArticleListFragment();
            }
        }
    });
}

private void setupUI() {
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mActionBar = getActionBar();
    mPagerAdapter = new TabsPagerAdapter(getFragmentManager(), rssService);

    mViewPager.setAdapter(mPagerAdapter);
    mActionBar.setHomeButtonEnabled(false);
    mActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Adding Tabs
    ...

    mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            mActionBar.setSelectedNavigationItem(position);
        }

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

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

@Override
protected void onResume() {
    super.onResume();
    reloadArticleListFragment();
}

@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
    mViewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

private void reloadArticleListFragment() {
    mPagerAdapter.setFilterType(filterType);
    if (mDataFragment != null) {
        mDataFragment.setFilterType(filterType);
        mDataFragment.refreshData(false);
    }
}
...
}

public abstract class AbstractDataFragment extends Fragment implements DataFragment {

...

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException("Activity must implement fragment's callbacks.");
    }
    callbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();
    callbacks = sDummyCallbacks;
}

@Override
public void refreshData(boolean force) {
    if (force) {
        if (rssService != null) {
            rssService = new RssService(getActivity());
        }
        rssService.execute(BLOG_URL);
    } else {
        setFilterType(filterType);
    }
    adapter.notifyDataSetChanged(); // NullPointerException is thrown here
}
}

public class ArticleListFragment extends AbstractDataFragment {
private ListView listView;

public static ArticleListFragment newInstance(SelectionType selectionType, FilterType filterType, int feedScope) {
    ArticleListFragment fragment = new ArticleListFragment();
    Bundle args = new Bundle();
    args.putSerializable(ARG_SELECTION_TYPE, selectionType);
    args.putSerializable(ARG_FILTER_TYPE, filterType);
    args.putInt(ARG_FEED_SCOPE, feedScope);
    fragment.setArguments(args);
    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.article_list, container, false);
    this.listView = (ListView) view.findViewById(R.id.listView);
    this.listView.setEmptyView(view.findViewById(R.id.emptyView));
    return view;
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    if (savedInstanceState != null) {
        if (savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
            setActivatedPosition(savedInstanceState.getInt(STATE_ACTIVATED_POSITION));
        }
    }
    // init image loader if it is not initialized before
    if (!ImageLoader.getInstance().isInited()) {
        initImageLoader();
    }
    initializeAdapter();
    // set click listener
    if (getDataView() != null) {
        getDataView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                getCallbacks().onItemSelected(String.valueOf(position));
            }
        });
    }
}
...
}

AbstractDataFragment.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener, DataFragment.Callbacks {

...

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // setup ui and instantiate some variables (missing in the example)

    mDataFragment = (AbstractDataFragment) mPagerAdapter.getItem(mViewPager.getCurrentItem());
    mAdapter = mDataFragment.getAdapter();
    rssService.execute(RssService.BLOG_URL);

    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    sharedPreferences.registerOnSharedPreferenceChangeListener(new SharedPreferences.OnSharedPreferenceChangeListener() {
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            if (key.equalsIgnoreCase("feedScope")) {
                mPagerAdapter.setFeedScope(Integer.parseInt(sharedPreferences.getString(key, "0")));
                reloadArticleListFragment();
            } else if (key.equalsIgnoreCase("countySelection")) {
                reloadArticleListFragment();
            }
        }
    });
}

private void setupUI() {
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mActionBar = getActionBar();
    mPagerAdapter = new TabsPagerAdapter(getFragmentManager(), rssService);

    mViewPager.setAdapter(mPagerAdapter);
    mActionBar.setHomeButtonEnabled(false);
    mActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Adding Tabs
    ...

    mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            mActionBar.setSelectedNavigationItem(position);
        }

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

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

@Override
protected void onResume() {
    super.onResume();
    reloadArticleListFragment();
}

@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
    mViewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

private void reloadArticleListFragment() {
    mPagerAdapter.setFilterType(filterType);
    if (mDataFragment != null) {
        mDataFragment.setFilterType(filterType);
        mDataFragment.refreshData(false);
    }
}
...
}

public abstract class AbstractDataFragment extends Fragment implements DataFragment {

...

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException("Activity must implement fragment's callbacks.");
    }
    callbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();
    callbacks = sDummyCallbacks;
}

@Override
public void refreshData(boolean force) {
    if (force) {
        if (rssService != null) {
            rssService = new RssService(getActivity());
        }
        rssService.execute(BLOG_URL);
    } else {
        setFilterType(filterType);
    }
    adapter.notifyDataSetChanged(); // NullPointerException is thrown here
}
}

public class ArticleListFragment extends AbstractDataFragment {
private ListView listView;

public static ArticleListFragment newInstance(SelectionType selectionType, FilterType filterType, int feedScope) {
    ArticleListFragment fragment = new ArticleListFragment();
    Bundle args = new Bundle();
    args.putSerializable(ARG_SELECTION_TYPE, selectionType);
    args.putSerializable(ARG_FILTER_TYPE, filterType);
    args.putInt(ARG_FEED_SCOPE, feedScope);
    fragment.setArguments(args);
    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.article_list, container, false);
    this.listView = (ListView) view.findViewById(R.id.listView);
    this.listView.setEmptyView(view.findViewById(R.id.emptyView));
    return view;
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    if (savedInstanceState != null) {
        if (savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
            setActivatedPosition(savedInstanceState.getInt(STATE_ACTIVATED_POSITION));
        }
    }
    // init image loader if it is not initialized before
    if (!ImageLoader.getInstance().isInited()) {
        initImageLoader();
    }
    initializeAdapter();
    // set click listener
    if (getDataView() != null) {
        getDataView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                getCallbacks().onItemSelected(String.valueOf(position));
            }
        });
    }
}
...
}

ArticleListFragment.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener, DataFragment.Callbacks {

...

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // setup ui and instantiate some variables (missing in the example)

    mDataFragment = (AbstractDataFragment) mPagerAdapter.getItem(mViewPager.getCurrentItem());
    mAdapter = mDataFragment.getAdapter();
    rssService.execute(RssService.BLOG_URL);

    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    sharedPreferences.registerOnSharedPreferenceChangeListener(new SharedPreferences.OnSharedPreferenceChangeListener() {
        @Override
        public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
            if (key.equalsIgnoreCase("feedScope")) {
                mPagerAdapter.setFeedScope(Integer.parseInt(sharedPreferences.getString(key, "0")));
                reloadArticleListFragment();
            } else if (key.equalsIgnoreCase("countySelection")) {
                reloadArticleListFragment();
            }
        }
    });
}

private void setupUI() {
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mActionBar = getActionBar();
    mPagerAdapter = new TabsPagerAdapter(getFragmentManager(), rssService);

    mViewPager.setAdapter(mPagerAdapter);
    mActionBar.setHomeButtonEnabled(false);
    mActionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Adding Tabs
    ...

    mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            mActionBar.setSelectedNavigationItem(position);
        }

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

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

@Override
protected void onResume() {
    super.onResume();
    reloadArticleListFragment();
}

@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {
    mViewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction ft) {

}

private void reloadArticleListFragment() {
    mPagerAdapter.setFilterType(filterType);
    if (mDataFragment != null) {
        mDataFragment.setFilterType(filterType);
        mDataFragment.refreshData(false);
    }
}
...
}

public abstract class AbstractDataFragment extends Fragment implements DataFragment {

...

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    if (!(activity instanceof Callbacks)) {
        throw new IllegalStateException("Activity must implement fragment's callbacks.");
    }
    callbacks = (Callbacks) activity;
}

@Override
public void onDetach() {
    super.onDetach();
    callbacks = sDummyCallbacks;
}

@Override
public void refreshData(boolean force) {
    if (force) {
        if (rssService != null) {
            rssService = new RssService(getActivity());
        }
        rssService.execute(BLOG_URL);
    } else {
        setFilterType(filterType);
    }
    adapter.notifyDataSetChanged(); // NullPointerException is thrown here
}
}

public class ArticleListFragment extends AbstractDataFragment {
private ListView listView;

public static ArticleListFragment newInstance(SelectionType selectionType, FilterType filterType, int feedScope) {
    ArticleListFragment fragment = new ArticleListFragment();
    Bundle args = new Bundle();
    args.putSerializable(ARG_SELECTION_TYPE, selectionType);
    args.putSerializable(ARG_FILTER_TYPE, filterType);
    args.putInt(ARG_FEED_SCOPE, feedScope);
    fragment.setArguments(args);
    return fragment;
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.article_list, container, false);
    this.listView = (ListView) view.findViewById(R.id.listView);
    this.listView.setEmptyView(view.findViewById(R.id.emptyView));
    return view;
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    if (savedInstanceState != null) {
        if (savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) {
            setActivatedPosition(savedInstanceState.getInt(STATE_ACTIVATED_POSITION));
        }
    }
    // init image loader if it is not initialized before
    if (!ImageLoader.getInstance().isInited()) {
        initImageLoader();
    }
    initializeAdapter();
    // set click listener
    if (getDataView() != null) {
        getDataView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                getCallbacks().onItemSelected(String.valueOf(position));
            }
        });
    }
}
...
}

if（rssService！=null）{ rssService=新的rssService（getActivity（））； }

我想你想给我

if（rssService==null）{ rssService=新的rssService（getActivity（））； }

---

你能出示>日志吗？谢谢你的回复。我已经更新了原始帖子并插入了stacktrace…谢谢你的帮助！你说得对。但这不是问题所在。此代码仅在force为true时使用（在我的情况下并非如此）。