Question

我有一个标签活动，我已经初始化了我的操作栏，它会根据片段动态变化。这是我基本上想要的功能。所以正在发生的是，当我运行应用程序时，NPR正在出现。我附加了tab活动java类，片段java类和log cat。

Bottoms_tab_activity.java

public class Bottom_Tabs_Activity extends AppCompatActivity{
    private TabLayout tabLayout;
    private ViewPager viewPager;

    private int[] tabIcons = {
            R.drawable.ic_friends,
            R.drawable.ic_map,
            R.drawable.ic_status,
            R.drawable.ic_chat,
            R.drawable.ic_profile

    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tabs);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        if (viewPager != null)
            setupViewPager(viewPager);
        else {
            Log.e("test", "i am null");
        }

        setupTabIcons();
    }
        private void setupTabIcons() {
            tabLayout.getTabAt(0).setIcon(tabIcons[0]);
            tabLayout.getTabAt(1).setIcon(tabIcons[1]);
            tabLayout.getTabAt(2).setIcon(tabIcons[2]);
            tabLayout.getTabAt(3).setIcon(tabIcons[3]);
            tabLayout.getTabAt(4).setIcon(tabIcons[4]);
        }

    private void setupViewPager(ViewPager viewPager)
    {
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFrag(new MapFragment(),"MAPS");
        adapter.addFrag(new PeopleFragment(),"PEOPLE");
        adapter.addFrag(new HomeFragment(),"HOME");
        adapter.addFrag(new ChatFragment(),"CHAT");
        adapter.addFrag(new ProfileFragment(),"PROFILE");

        viewPager.setAdapter(adapter);
    }
    class ViewPagerAdapter extends FragmentStatePagerAdapter
    {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();
        public ViewPagerAdapter(FragmentManager manager)
        {
            super(manager);
        }
        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }
        @Override
        public int getCount() {
            return mFragmentList.size();
        }
        public void addFrag(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }
        @Override
        public CharSequence getPageTitle(int position) {

            // return null to display only the icon
            return null;
        }
    }
    public void setActionBarTitle(String title) {
        TextView s= (TextView) getSupportActionBar().getCustomView().findViewById(R.id.tv);
        s.setText(title);
    }
}

Homefragment.java

public class HomeFragment extends Fragment {

    public HomeFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        ((Bottom_Tabs_Activity)getActivity()).setActionBarTitle("Status");
        return inflater.inflate(R.layout.homefragment, container, false);
    }
}

logcat的

04-07 11:12:55.097 28437-28437/com.example.vikrant.safeshelter E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.vikrant.safeshelter, PID: 28437
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.v7.app.ActionBar.getCustomView()' on a null object reference
at com.example.vikrant.safeshelter.Bottom_Tabs_Activity.setActionBarTitle(Bottom_Tabs_Activity.java:183)
at com.example.vikrant.safeshelter.HomeFragment.onCreateView(HomeFragment.java:32)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1974)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617)
at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:570)
at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:164)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1177)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:608)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:570)
at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:551)
at android.support.design.widget.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:1627)
at android.support.design.widget.TabLayout.selectTab(TabLayout.java:837)
at android.support.design.widget.TabLayout.selectTab(TabLayout.java:809)
at android.support.design.widget.TabLayout$Tab.select(TabLayout.java:1077)
at android.support.design.widget.TabLayout$1.onClick(TabLayout.java:643)
at android.view.View.performClick(View.java:4759)
at android.view.View$PerformClick.run(View.java:19770)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5234)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:909)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:704)

bottoms_tabs_activity的第183行是

TextView s= (TextView) getSupportActionBar().getCustomView().findViewById(R.id.tv);

家庭片段的第32行是

((Bottom_Tabs_Activity)getActivity()).setActionBarTitle("Status");

Answer 1

请尝试以下操作：

((Bottom_Tabs_Activity)getActivity()).setActionBarTitle("Status"); 在onActivityCreated的{{1}}方法中。

当我将它与片段一起使用时，Action Bar会给出空指针异常

1 个答案: