为什么在Android中应用首先调用的ViewModel观察者?

问题描述

查看代码:

class ProductFragment : Fragment(R.layout.fragment_product) {
    private val viewModel by viewModels<ProductViewModel>()
    private lateinit var adapter: ProductAdapter
    private var productList: List<Products> = ArrayList()

    private var _binding: FragmentProductBinding? = null
    private val binding get() = _binding!!

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

        _binding = FragmentProductBinding.bind(view)

        adapter = ProductAdapter(context, productList)

        binding.apply {
            recyclerView.setHasFixedSize(true)
            recyclerView.adapter = adapter
            showLog("LIST1: "+ productList.size)
        }

        viewModel.product().observe(viewLifecycleOwner) {
            productList = it
            adapter.notifyDataSetChanged()
        }
    }

在"it"内部我的尺寸正确，但问题是"recyclerView.adapter = adapter"首先调用而不是观察者，所以适配器中getItemCount的大小始终为0.

Inside "it" I'm getting correct size, but the thing is "recyclerView.adapter = adapter" is calling first instead of observer, so getItemCount size is always coming 0 inside adapter.

推荐答案

已解决:

@AndroidEntryPoint
class ProductFragment : Fragment(R.layout.fragment_product) {
    private val viewModel by viewModels<ProductViewModel>()
    private var _binding: FragmentProductBinding? = null
    private val binding get() = _binding!!

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        _binding = FragmentProductBinding.bind(view)

        viewModel.product().observe(viewLifecycleOwner, Observer { productList ->
            binding.recyclerView.also {
                it.setHasFixedSize(true)
                it.adapter = ProductAdapter(context, productList)
            }
        })
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

}

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