Fragment中RecyclerView报‘No adapter attached’警告的解决方法

问题原因 #

当前代码中，你仅在kanjiViewModel.kanjiList的观察者回调里为RecyclerView设置adapter，但LiveData的数据回调是异步的——Fragment初始化RecyclerView后，LiveData还未返回数据的这段时间里，RecyclerView已经开始执行布局流程，发现未绑定adapter，就会抛出该警告。虽然后续数据返回后能正常显示，但警告源于布局时机早于adapter绑定时机。

解决办法 #

在初始化RecyclerView的阶段（initUI方法内）就直接给两个RecyclerView绑定adapter，数据更新时仅调用submitList更新adapter的数据即可，无需重复设置adapter。

修改后的代码示例 #

class SpacedFragment : Fragment() {
    private lateinit var kanjiViewModel : KanjiViewModel
    private lateinit var spacedRecyclerAdapter : SpacedRecyclerAdapter
    private lateinit var day1Adapter: SpacedRecyclerAdapter
    private var _binding : FragmentSpacedBinding? = null
    private val binding get() = _binding!!
    
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View {
        _binding = FragmentSpacedBinding.inflate(inflater,container,false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        initUI()
    }

    private fun initUI() {
        val dao = KanjiDatabase.getInstance(requireContext()).dao()
        val repository = KanjiRepository(dao)
        val factory = KanjiViewModelFactory(repository)
        kanjiViewModel = ViewModelProvider(this,factory)[KanjiViewModel::class.java]
        
        // 初始化adapter
        spacedRecyclerAdapter = SpacedRecyclerAdapter()
        day1Adapter = SpacedRecyclerAdapter()
        
        // 绑定layoutManager和adapter
        binding.spacedRecyclerview.apply {
            layoutManager = GridLayoutManager(context,5)
            adapter = spacedRecyclerAdapter
        }
        
        binding.spacedRecyclerviewDay1.apply {
            layoutManager = GridLayoutManager(context,5)
            adapter = day1Adapter
        }
        
        getData()
    }

    private fun getData() {
        kanjiViewModel.kanjiList.observe(viewLifecycleOwner, { data ->
            // 仅更新数据集合
            spacedRecyclerAdapter.submitList(data.filter { it.spacedstatus == 0 })
            day1Adapter.submitList(data.filter { it.Japanese_Language_Proficiency_Test == 4 })
        })
    }
    
    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }
}

额外说明 #

• 该做法符合RecyclerView的使用规范：adapter应在RecyclerView布局前完成绑定，后续仅更新数据集合即可，既避免警告也能减少不必要的布局刷新。
• 重复设置adapter可能引发潜在的性能问题或布局异常，仅更新数据是更高效的操作方式。

内容的提问来源于stack exchange，提问作者Bradboyee