无法使用 Kotlin 协同程序解析 recyclerview 中的数据

Question

我正在从服务器获取数据并尝试使用 coroutines.Though 在回收站视图中解析它数据已成功获取，但我无法从我的嵌套 json.[= 解析特定键17=]

这里是 JSON 回复：

{
"status": "200",
"message": "Success",
"result": [
    {
        "_id": "60f516fa846e059e2f19c50c",
        "category": "Shirts",
        "sku": [
            {
                "name": "Oxford shirt",
                "brand": "John players",
                "price": "25",
                "color": "Blue",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/shi1.jpg?alt=media&token=64779194-e3b5-484f-a610-c9a20648b64c"
            },
            {
                "name": "Buttoned down",
                "brand": "Gap originals",
                "price": "45",
                "color": "Pink",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/shi2.jpg?alt=media&token=0b207b90-f1bc-4771-b877-809648e6bdc1"
            },
            {
                "name": "Collared",
                "brand": "Arrow",
                "price": "30",
                "color": "White",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/shi3.jpg?alt=media&token=2c1bb3f8-e739-4f09-acbc-aa11fed795e3"
            },
            {
                "name": "Printed",
                "brand": "John players",
                "price": "30",
                "color": "Olive green",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/shi4.jpg?alt=media&token=666f94bf-4769-44fe-a909-3c81ca9262f7"
            },
            {
                "name": "Hoodie",
                "brand": "Levis",
                "price": "44",
                "color": "Yellow",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/shi5.jpg?alt=media&token=65fccef4-a882-4278-b5df-f00eb2785bf1"
            }
        ]
    },
    {
        "_id": "60f51c37846e059e2f19c50f",
        "category": "Shoes",
        "sku": [
            {
                "name": "Sneakers",
                "brand": "Puma",
                "price": "35",
                "color": "Black and white",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/sho1.jpg?alt=media&token=d078988d-9e85-4313-bb4a-c9d46e09f0b9"
            },
            {
                "name": "Running shoe",
                "brand": "Nike",
                "price": "99",
                "color": "Multicolor",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/sho2.jpg?alt=media&token=ed2e7387-3cf6-44df-9f7d-69843eb0bcdf"
            },
            {
                "name": "Yezzy",
                "brand": "Adidas",
                "price": "349",
                "color": "Gray",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/sho3.jpg?alt=media&token=2c37ef76-37bb-4bdd-b36c-dea32857291f"
            },
            {
                "name": "Sneakers",
                "brand": "Puma",
                "price": "79",
                "color": "Black",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/sho4.jpg?alt=media&token=4acd763e-8b93-47cd-ba45-92f34af4cf83"
            },
            {
                "name": "Joyride running",
                "brand": "Nike",
                "price": "80",
                "color": "White",
                "img": "https://firebasestorage.googleapis.com/v0/b/koovs-1ff31.appspot.com/o/sho5.jpg?alt=media&token=e3780dcc-52cb-49d5-9791-e0a44870716c"
            }
        ]
    
       }
    ]
}

我想获取类别。

下面是数据class

Product.kt

data class Product(
  val message: String,
  val result: List<Result>,
  val status: String
)

Result.kt

data class Result(
  val _id: String,
  val category: String,
  val sku: List<Sku>
)

ApiService.kt

interface ApiService {

  @GET("getProducts")
  suspend fun getCategories(): Response<Product>
}

CategoriesViewModel.kt

class CategoriesViewModel: ViewModel() {

private var categoryList: MutableLiveData<List<Result>> = MutableLiveData()

fun getAllCategory(): LiveData<List<Result>> {

    viewModelScope.launch(Dispatchers.IO) {

        val retrofit = RetrofitClient.getRetrofitClient().create(ApiService::class.java)
        val response = retrofit.getCategories()

        if (response.isSuccessful) {
            categoryList.postValue(response.body()!!.result)
        }
    }
    return categoryList
  }
}

CategoryAdapter.kt

class CategoryAdapter(private val context: Context,private val categories:List<Result>): RecyclerView.Adapter<CategoryAdapter.ViewHolder>() {

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CategoryAdapter.ViewHolder {
   return ViewHolder(ParentRowBinding.inflate(LayoutInflater.from(parent.context),parent,false))
}

override fun onBindViewHolder(holder: ViewHolder, position: Int) {

    val model = categories[position]
    holder.binding.catTitle.text = model.category
}

override fun getItemCount(): Int {
    return categories.size
}

class ViewHolder(val binding:ParentRowBinding): RecyclerView.ViewHolder(binding.root)
}

HomeFragment.kt

class HomeFragment : Fragment() {

private var binding: FragmentHomeBinding? = null
private lateinit var adapter: CategoryAdapter

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    binding = FragmentHomeBinding.inflate(inflater,container,false)

    binding!!.parentRecycler.setHasFixedSize(true)
    binding!!.parentRecycler.layoutManager = LinearLayoutManager(activity)

    val viewModel = ViewModelProvider(this).get(CategoriesViewModel::class.java)

    viewModel.getAllCategory().observe(viewLifecycleOwner, Observer { t ->

        val len = t.size

        if(len > 0){

            for(i in 0 until len){
                Log.d("hell", t[i].category.toString())
            }
        }
    })

    return binding!!.root
}

override fun onDestroy() {
    super.onDestroy()
    binding = null
}
}

在这里我以某种方式获取了类别，但我不知道如何将其传递给适配器以便我可以在 recyclerview 中显示它。

Answer 1

您必须将 Adapter 分配给 getAllCategory 观察者中的 RecyclerView，如下所示

viewModel.getAllCategory().observe(viewLifecycleOwner, Observer {
    if(!it.isNullOrEmpty()){
        binding!!.parentRecycler.adapter = CategoryAdapter(requireContext(), it)
        // This will bind the Result list received to the recycler view
    }
})

Answer 2

在您的 HomeFragment 中，您需要将 Adapter 设置为您的 RecyclerView

 binding!!.parentRecycler.adapter= CategoryAdapter(requireContext(),t)

HomeFragment完整代码如下

class HomeFragment : Fragment() {

private var binding: FragmentHomeBinding? = null
private lateinit var adapter: CategoryAdapter

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    binding = FragmentHomeBinding.inflate(inflater,container,false)

    binding!!.parentRecycler.setHasFixedSize(true)
    binding!!.parentRecycler.layoutManager = LinearLayoutManager(activity)

    val viewModel = ViewModelProvider(this).get(CategoriesViewModel::class.java)

    viewModel.getAllCategory().observe(viewLifecycleOwner, Observer { t ->

        val len = t.size

        if(len > 0){
            //add this line
            binding!!.parentRecycler.adapter= CategoryAdapter(requireContext(),t) 

            for(i in 0 until len){
                Log.d("hell", t[i].category.toString())
            }
        }
    })

    return binding!!.root
}

override fun onDestroy() {
    super.onDestroy()
    binding = null
}
}

Answer 3

我想最好的方法是从 ListAdapter 继承您的适配器。因为与 RecyclerView.Adapter 不同，它内置了对提交新列表的支持。

这样更高效、更快速，并且不需要创建新的适配器对象或完全更新 RecyclerView 中的所有项目。由于 DiffUtil，只会更新实际更改的项目。

所以你 CategoryAdapter 应该变成：

class CategoryAdapter : ListAdapter<Result, CategoryAdapter.ViewHolder>(DIFF_CALLBACK) {

    companion object {
        val DIFF_CALLBACK = object : DiffUtil.ItemCallback<Result>() {
            override fun areItemsTheSame(oldItem: Inspection.Type, newItem: Inspection.Type) = oldItem._id == newItem._id
            override fun areContentsTheSame(oldItem: Inspection.Type, newItem: Inspection.Type) = oldItem == newItem
        }
    }

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CategoryAdapter.ViewHolder {
   return ViewHolder(ParentRowBinding.inflate(LayoutInflater.from(parent.context),parent,false))
}

override fun onBindViewHolder(holder: ViewHolder, position: Int) {

    val model = getItem(position)
    holder.binding.catTitle.text = model.category
}

class ViewHolder(val binding:ParentRowBinding): RecyclerView.ViewHolder(binding.root)
}

并且在您的 onCreateView 中：

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    binding = FragmentHomeBinding.inflate(inflater,container,false)

    binding!!.parentRecycler.setHasFixedSize(true)
    binding!!.parentRecycler.layoutManager = LinearLayoutManager(activity)
    adapter = CategoryAdapter()
    binding!!.parentRecycler.adapter = adapter

    val viewModel = ViewModelProvider(this).get(CategoriesViewModel::class.java)

    viewModel.getAllCategory().observe(viewLifecycleOwner, Observer { categories ->
        adapter.submitList(categories)
    })

    return binding!!.root
}

请注意，在上面的代码中，您根本没有创建适配器实例，也没有将其分配给回收器。所以它根本不会显示任何东西。

在我的示例中，我在 onCreateView 中创建了一个适配器并将其分配给回收器。在 Observer 中，我们将从 ViewModel 接收到的数据传递给适配器。

Answer 4

是的，正如@dhiraj-uchil 提到的，这里的问题不是设置丢失的适配器。我也会制作 binding lateinit 或本地。我也会提取 context，并在其他地方使用它。

 val binding = FragmentHomeBinding.inflate(inflater, container, false)
 val context = requireContext()
 binding.parentRecycler.adapter= CategoryAdapter(context, t)

关于从 JSON 制作数据 class 对象，我制作了一个工具，除其他外，生成这样的 classes:

https://kt.academy/json

无法使用 Kotlin 协同程序解析 recyclerview 中的数据

Unable to parse data in recycler view using Kotlin co-routines

android

json

kotlin

android-mvvm

kotlin-coroutines