片段中的ViewPager和TabLayout。一个空对象的setAdapter参考

我试图在片段中添加viewPager。但是，当我开始我的应用程序收到此：片段中的ViewPager和TabLayout。一个空对象的setAdapter参考

显示java.lang.NullPointerException：试图调用虚拟方法无效android.support.v4.view.ViewPager.setAdapter（android.support.v4.view.PagerAdapter ）”上的空对象引用

我MainFragment：

public class YourTasksFragment extends Fragment { 

@Bind(R.id.viewpager) 
ViewPager viewPager; 

@Bind(R.id.tabs) 
TabLayout tabLayout; 

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    View v = inflater.inflate(R.layout.fragment_your_tasks, container, false); 
    return v; 
} 

@Override 
public void onViewCreated(View view, Bundle savedInstanceState) { 
    super.onViewCreated(view, savedInstanceState); 
    setupViewPager(viewPager); 
    tabLayout.setupWithViewPager(viewPager); 
} 

private void setupViewPager(ViewPager viewPager) { 
    ViewPagerAdapter adapter = new ViewPagerAdapter(getChildFragmentManager()); 
    adapter.addFragment(new OneFragment(), "ONE"); 
    adapter.addFragment(new TwoFragment(), "TWO"); 
    viewPager.setAdapter(adapter); 
} 

class ViewPagerAdapter extends FragmentPagerAdapter { 
    private final List<Fragment> fragmentList = new ArrayList<>(); 
    private final List<String> fragmentTitleList = new ArrayList<>(); 

    public ViewPagerAdapter(FragmentManager childFragmentManager) { 
     super(childFragmentManager); 
    } 

    @Override 
    public Fragment getItem(int position) { 
     return fragmentList.get(position); 
    } 

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

    public void addFragment(Fragment fragment, String title) { 
     fragmentList.add(fragment); 
     fragmentTitleList.add(title); 
    } 

    @Override 
    public CharSequence getPageTitle(int position) { 
     return fragmentTitleList.get(position); 
    } 
} 
}

布局：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:app="http://schemas.android.com/apk/res-auto" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 

    <android.support.design.widget.TabLayout 
     android:id="@+id/tabs" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     app:tabMode="fixed" 
     app:tabGravity="fill"/> 

<android.support.v4.view.ViewPager 
    android:id="@+id/viewpager" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    app:layout_behavior="@string/appbar_scrolling_view_behavior" />

来源

2016-04-22 MobileDev

尝试手动链接viewpager，并验证它是否是正确的布局。 –

请参阅http://www.gadgetsaint.com/android/create-viewpager-tabs-android/#.WPuppVN97BI – ASP

你忘了在onCreateView（）中设置Butterknife，因此变量永远不会被初始化。

这样做：

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    View v = inflater.inflate(R.layout.fragment_your_tasks, container, false); 
    Butterknife.bind(this,v); 
    return v; 
}

希望它能帮助！

来源

2016-04-22 22:37:45

这是什么错误！我很盲目:)谢谢。问题已解决。 – MobileDev

你忘了在方法onCreateView上添加Butterknife.bind（this，v）。这是绑定视图所必需的。

@Nullable 
@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    View v = inflater.inflate(R.layout.fragment_your_tasks, container, false); 
    Butterknife.bind(this,v); 
    return v; 
}

来源

2016-04-22 21:58:10

片段中的ViewPager和TabLayout。一个空对象的setAdapter参考

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