Android Fragment中调用requireView()抛出「did not return a View from onCreateView() or this was called before onCreateView()」错误的原因咨询

Problem Description #

I'm working on a project where the code has no syntax errors, but when building and running the app, I get the error "did not return a View from onCreateView() or this was called before onCreateView()" when executing viewPager2 = requireView().findViewById(R.id.vpager) in my MyFragment's onCreateView method. Here's my Fragment code:

class MyFragment : Fragment(R.layout.fragment_my) {
    lateinit var viewPager2: ViewPager2
    lateinit var adapter: VideoAdapter

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        /**set find id*/
        viewPager2 = requireView().findViewById(R.id.vpager)
        /**set database*/
        val mDataBase = Firebase.database.getReference("videos")
        val options = FirebaseRecyclerOptions.Builder<VideoModel>()
            .setQuery(mDataBase,VideoModel::class.java)
            .build()
        /**set adapter*/
        adapter = VideoAdapter(options)
        viewPager2.adapter = adapter
        return view
    }

    override fun onStart() {
        super.onStart()
        adapter.startListening()
    }

    override fun onStop() {
        super.onStop()
        adapter.stopListening()
    }
}

Root Cause #

Let's break down why this error pops up:

1. You're using the Fragment(R.layout.fragment_my) constructor, which automatically handles inflating your layout. When you override onCreateView, the super.onCreateView() call already returns the inflated view.
2. The critical issue is that you're calling requireView() before returning the view from onCreateView. requireView() is meant to fetch the Fragment's already attached view, but at this point in the lifecycle, the view hasn't been fully linked to the Fragment yet—since onCreateView hasn't finished executing and returned the view.
3. On top of that, your current code returns view without properly initializing it from the super call, which adds to the lifecycle mismatch.

Fixes & Solutions #

Solution 1: Use onViewCreated (Recommended) #

The onViewCreated lifecycle method runs right after onCreateView returns the view, so the Fragment's view is fully attached and safe to interact with. This is the cleanest approach for view-related setup:

class MyFragment : Fragment(R.layout.fragment_my) {
    lateinit var viewPager2: ViewPager2
    lateinit var adapter: VideoAdapter

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        // Use the provided view parameter directly (no need for requireView())
        viewPager2 = view.findViewById(R.id.vpager)
        
        // Initialize Firebase and adapter
        val mDataBase = Firebase.database.getReference("videos")
        val options = FirebaseRecyclerOptions.Builder<VideoModel>()
            .setQuery(mDataBase, VideoModel::class.java)
            .build()
        
        adapter = VideoAdapter(options)
        viewPager2.adapter = adapter
    }

    override fun onStart() {
        super.onStart()
        adapter.startListening()
    }

    override fun onStop() {
        super.onStop()
        adapter.stopListening()
    }
}

Solution 2: Fix onCreateView to Use the Inflated View #

If you prefer to keep initialization within onCreateView, first capture the view returned by super.onCreateView(), then use that view to find your ViewPager2:

class MyFragment : Fragment(R.layout.fragment_my) {
    lateinit var viewPager2: ViewPager2
    lateinit var adapter: VideoAdapter

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Get the inflated view from the super call
        val view = super.onCreateView(inflater, container, savedInstanceState)
        
        // Use this view to find your ViewPager2 (no requireView() needed)
        viewPager2 = view!!.findViewById(R.id.vpager)
        
        // Initialize Firebase and adapter
        val mDataBase = Firebase.database.getReference("videos")
        val options = FirebaseRecyclerOptions.Builder<VideoModel>()
            .setQuery(mDataBase, VideoModel::class.java)
            .build()
        
        adapter = VideoAdapter(options)
        viewPager2.adapter = adapter
        
        return view
    }

    override fun onStart() {
        super.onStart()
        adapter.startListening()
    }

    override fun onStop() {
        super.onStop()
        adapter.stopListening()
    }
}

Why Solution 1 is Preferred #

onViewCreated is explicitly designed for post-view-creation setup. It separates layout inflation logic (handled by the Fragment(R.layout.fragment_my) constructor) from view initialization, making your code more organized and aligned with Android's Fragment lifecycle best practices.

内容的提问来源于stack exchange，提问作者user10991969