Java setViewPager返回NullPointerException

所以我遇到了这个问题。我正在尝试用一些选项卡制作简单的操作栏。不知何故，我得到了NullPointerException，但我不知道如何修复它。下面是一些代码：

MainActivity.java

public class MainActivity extends FragmentActivity {
    ViewPager Tab;
    TabPagerAdapter TabAdapter;
    ActionBar actionBar;
    PagerSlidingTabStrip tabs;

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

        tabs = (PagerSlidingTabStrip) findViewById(R.id.tabs);
        Tab = (ViewPager) findViewById(R.id.pager);
        TabAdapter = new TabPagerAdapter(getSupportFragmentManager());

        Tab.setAdapter(TabAdapter);
        tabs.setViewPager(Tab); //line 27 where the error appears

        tabs.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {

                actionBar = getActionBar();
                actionBar.setSelectedNavigationItem(position);
            }
        });
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <com.astuetz.PagerSlidingTabStrip
        android:id="@+id/tabs"
        android:layout_width="match_parent"
        android:layout_height="48dip" />

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity" />

</RelativeLayout>

这是我的适配器：

TabPagerAdapter.java

public class TabPagerAdapter extends FragmentStatePagerAdapter {
    public TabPagerAdapter(FragmentManager fm) {
        super(fm);
        // TODO Auto-generated constructor stub
    }

    @Override
    public Fragment getItem(int i) {
        switch (i) {
        case 0:
            //Fragement for Stories Tab
            return new Stories();
        case 1:
           //Fragment for Legends Tab
            return new Legends();
        case 2:
            //Fragment for Multimedia Tab
            return new Multimedia();

        case 3:
            //Fragment for Books Tab
            return new Books();
        }
        return null;

    }

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return 4; //No of Tabs
    }
}

---

提前感谢您的帮助

您需要覆盖

PagerAdapter

中的

getPageTitle（）

，并提供

PagerSlidingTastrip

可以获得的标题。

错误，因为适配器中没有数据。。我应该在适配器中输入哪些数据？我为它编辑了代码。

public CharSequence getPageTitle(int position) {

            if (position == 0)
            {
                return "Stories";
            }
            if (position == 1)
            {
                return "Legends";
            }
            if (position == 2)
            {
                return "Multimedia";
            }
            if (position == 3)
            {
                return "Books";
            } 
            return null;
        }

public CharSequence getPageTitle(int position) {

            if (position == 0)
            {
                return "Stories";
            }
            if (position == 1)
            {
                return "Legends";
            }
            if (position == 2)
            {
                return "Multimedia";
            }
            if (position == 3)
            {
                return "Books";
            } 
            return null;
        }