android - 在 onTabSelected 中玩 fragment

Question

亲爱的，

我搜索了这个问题超过一天，但没有找到。我完全执行此处发布的代码:

Adding Navigation Tabs

我的 onTabSelected 代码如下:

public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // Check if the fragment is already initialized
        if (mFragment == null) {
            // If not, instantiate and add it to the activity
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.add(R.id.alert_fragment_container, mFragment, mTag);
        } else {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);
        }

        // prepare adapter for ExpandableListView

        Log.i("After Adapter Created", "Passed");

        final ExpandableListAdapter expListAdapter = new AlertsAdapter(
                mActivity, myAlerts, violations);

        Log.i("After Adapter Initialized", "Passed");

       ((MyCustomFragment)mFragment).violations.setAdapter(expListAdapter);
    }

代码在最后一行之前工作正常，我需要在 onCreateView 中为在 MyCustomFragment 中初始化的公共(public)静态列表设置适配器，这里是我的 fragment 代码:

public class MyCustomFragment extends Fragment {

    public MyCustomFragment() {
    }

    public static ExpandableListView violations; 

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_alerts_poi, container, false);

        violations = (ExpandableListView) rootView.findViewById(R.id.POIAlertList);

        Log.i("onCreateView POI", "Called");

        return rootView;
    }
}

它给出空指针错误。通过我的调试日志，我注意到此日志 Log.i("onCreateView POI", "Called"); 出现在此 Log.i("After Adapter Initialized", "Passed");。这意味着我正在尝试为尚未初始化的 fragment 设置适配器。

这正是我面临的问题，我需要根据 onTabSelected 中的选项卡选择向 ExpandableListView 提供数据。

我做错了什么？什么是最好的解决方案？

问候，

Answer 1

看来你需要一个ViewPager，我几天前刚刚实现了一个导航选项卡，这是我的代码，它在 4 个 fragment 之间导航:

public class MainActivity extends FragmentActivity implements ActionBar.TabListener{
private ActionBar actionBar;
private ViewPager mViewPager;
private AppSectionsPagerAdapter mAppSectionsPagerAdapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mAppSectionsPagerAdapter = new AppSectionsPagerAdapter(getSupportFragmentManager());
    actionBar=getActionBar();
    actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mAppSectionsPagerAdapter);
    mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            actionBar.setSelectedNavigationItem(position);
        }
    });
    actionBar.addTab(actionBar.newTab().setIcon(R.drawable.icon1).setTabListener(this));
    actionBar.addTab(actionBar.newTab().setIcon(R.drawable.icon2).setTabListener(this));
    actionBar.addTab(actionBar.newTab().setIcon(R.drawable.icon3).setTabListener(this));
    actionBar.addTab(actionBar.newTab().setIcon(R.drawable.icon4).setTabListener(this));     
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // TODO Auto-generated method stub
    getMenuInflater().inflate(R.menu.action_menu, menu);
    return true;
}

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

}

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

}

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

}

这是适配器:

public class AppSectionsPagerAdapter extends FragmentPagerAdapter {
public AppSectionsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int i) {
    switch (i) {
        case 0:
            return new Fragment1();
        case 1:
            return new Fragment2();
        case 2:
            return new Fragment3();
        case 3: 
            return new Fragment4();
    }
    return null;
}

@Override
public int getCount() {
    return 4;
}

}