android - TabLayout设置ViewPager时出现空指针异常

Question

我有一个 fragment 将包含另外两个可以通过 TabLayout 访问的 fragment

我有以下 Kotlin 代码:

class TutorialFragment : Fragment() {

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {

        val tutorialview = inflater.inflate(R.layout.fragment_tutorial, container, false )

        tutorialview.tutorialViewPager.adapter = TutorialFragmentPagerAdapter(context!!, fragmentManager!!)

        //Null Pointer Exception on this line 
        tabBar.setupWithViewPager(tutorialview.tutorialViewPager)


        return tutorialview
    }

    companion object {
        fun newInstance() = TutorialFragment()
    }
}

我的代码因异常而崩溃:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.TabLayout.setupWithViewPager(android.support.v4.view.ViewPager)' on a null object reference
        at com.vedantroy.animefacekeyboard.home.tutorial.TutorialFragment.onCreateView(TutorialFragment.kt:23) 

更新 1 -

根据Tuby的建议，

我将我的代码更改为:

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {

    Log.d("KEYBOARD-APP","Inside tutorial fragment onCreate()...")
    val tutorialView = inflater.inflate(R.layout.fragment_tutorial, container, false )
    tutorialView.tutorialViewPager.adapter = TutorialFragmentPagerAdapter(fragmentManager!!)
    tutorialView.tabBar.setupWithViewPager(tutorialView.tutorialViewPager)

    return tutorialView
}

但是，虽然 fragment 本身现在正在显示，但选项卡并未显示。

Answer 1

错误清楚地表明 TabLayout 为空

尝试改变

tabBar.setupWithViewPager(tutorialview.tutorialViewPager)

到

tutorialview.tabBar.setupWithViewPager(tutorialview.tutorialViewPager)