无法使用房间数据库中的视图 model 更新我的 recyclerView，每个项目都会编辑前一个，而不是它在 recyclerView 中的项目 ID

Question

当我尝试用房间数据库中的视图 model 更新我的 recyclerView 时，每个 id 都会编辑前一个，而不是它在 recyclerView 中的项目 id。 我使用 adapterposition 将数据从 (EditCartFragment) 中的 recyclerView 项目传递到单击按钮上的 (EditSingleItemFragment)。

EditCartFragment.kt

class EditCartFragment : Fragment(), CommunicatorEdit{
    //Then MyCart data is ignored and we took our data from local database
    private val myCartItems = ArrayList<MyCartItemsDatabase>()
    private val myCartEditAdapter = MyCartEditAdapter(myCartItems, this)
    //Our ViewModel instance
    private lateinit var cartViewModel: CartViewModel
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        myCartDynamic.layoutManager = LinearLayoutManager(context, RecyclerView.VERTICAL, false)
        myCartDynamic.adapter = myCartEditAdapter
        //addData()
        //Setting my view model and my dynamic list
        cartViewModel = ViewModelProvider(this)[CartViewModel::class.java]
        cartViewModel.readAllData.observe(viewLifecycleOwner) { cart ->
            myCartEditAdapter.setData(cart)
        }
    }

    override fun passData(position: Int, title: String, image: Bitmap, price: Double, priceI: Double, num: Int, des: String) {
        val bundle = Bundle()
        bundle.putInt("edit_pos", position)
        bundle.putString("edit_name", title)
        bundle.putString("edit_image", getImageUri(requireContext(), image).toString())
        bundle.putDouble("edit_price", price)
        bundle.putDouble("edit_priceI", priceI)
        bundle.putInt("edit_num", num)
        bundle.putString("edit_des", des)

        val transaction = this.parentFragmentManager.beginTransaction()
        val editSingleItemFragment = EditSingleItemFragment()
        editSingleItemFragment.arguments = bundle

        transaction.replace(R.id.fragment_container, editSingleItemFragment)
        transaction.addToBackStack("editSI_fragment").setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
        transaction.commit()
    }

    //Converting bitmap image to URL
    private fun getImageUri(inContext: Context, inImage: Bitmap): Uri? {
        val bytes = ByteArrayOutputStream()
        inImage.compress(Bitmap.CompressFormat.JPEG, 100, bytes)
        val path = MediaStore.Images.Media.insertImage(
            inContext.contentResolver,
            inImage,
            "Title",
            null
        )
        return Uri.parse(path)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_edit_cart, container, false)
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment MyCartFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            EditCartFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

CartEditAdapter.kt

class CartEditAdapter(private var cartItems: List<CartItemsDatabase>, private val listener: CommunicatorEdit):
    RecyclerView.Adapter<CartEditAdapter.MyViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val cartView = LayoutInflater.from(parent.context).inflate(R.layout.edit_cart_items, parent, false)
        return MyViewHolder(cartView)
    }

    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        val newCart = cartItems[position]
        holder.cartedImg.load(newCart.cartImage){
            crossfade(true)
            transformations(CircleCropTransformation())
            placeholder(R.drawable.ic_launcher_foreground)
        }
        holder.cartedTitle.text = newCart.cartTitle.toString()
        holder.cartedItemNum.text = newCart.cartNum.toString()
        holder.cartedLPriceValue.text = newCart.cartPriceL.toString()
        holder.cartedIPriceValue.text = newCart.cartPriceI.toString()
        holder.cartedDes.text = newCart.cartDes.toString()
    }

    //Setting data from database
    fun setData(myCartComingItem: List<CartItemsDatabase>){
        this.cartItems = myCartComingItem
        notifyDataSetChanged()
    }

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

    inner class MyViewHolder constructor(itemView: View): RecyclerView.ViewHolder(itemView), View.OnClickListener{

        init {
            //Setting decrease items
            itemView.editMyItem.setOnClickListener(this)
        }

        override fun onClick(v: View?) {
            val position = adapterPosition
            val image = cartItems[adapterPosition].cartImage
            val name =  cartItems[adapterPosition].cartTitle
            val price = cartItems[adapterPosition].cartPriceL
            val priceI = cartItems[adapterPosition].cartPriceI
            val num = cartItems[adapterPosition].cartNum
            val des = cartItems[adapterPosition].cartDes
            if (position != RecyclerView.NO_POSITION) {
                listener.passData(position,name!!, image!!, price!!, priceI!!, num!!, des!!)
            }
        }

        val cartedImg: ShapeableImageView = itemView.myCartedImg
        val cartedTitle: TextView = itemView.myCartedTitle
        val cartedItemNum: TextView = itemView.myCartItemNum
        val cartedLPriceValue: TextView = itemView.localPriceCart
        val cartedIPriceValue: TextView = itemView.localPriceCartA
        val cartedDes: TextView = itemView.myCartedDes
    }
}

EditSingleItemFragment.kt 文件

class EditSingleItemFragment : Fragment() {
    //First, we have to initialize our view model
    private lateinit var cartViewModel: CartViewModel
    private var editPos: Int?= null
    private var editTitle: String = ""
    private var editImage: String = ""
    private var editPriceL: Double = 0.0
    private var editPriceI: Double = 0.0
    private var editNum: Int = 0
    private var editDes: String = ""
    // TODO: Rename and change types of parameters
    private var param1: String? = null
    private var param2: String? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        arguments?.let {
            param1 = it.getString(ARG_PARAM1)
            param2 = it.getString(ARG_PARAM2)
        }
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        editPos = arguments?.getInt("edit_pos")
        editTitle = arguments?.getString("edit_name").toString()
        editImage = requireArguments().getString("edit_image").toString()
        editPriceL = requireArguments().getDouble("edit_price")
        editPriceI = requireArguments().getDouble("edit_priceI")
        editNum = requireArguments().getInt("edit_num")
        editDes = arguments?.getString("edit_des").toString()

        editSTitle.text = editTitle
        editSImg.load(editImage){
            crossfade(true)
            transformations(CircleCropTransformation())
            placeholder(R.drawable.ic_launcher_foreground)
        }
        editSLPrice.text = editPriceL.toString()
        editSIPrice.text = editPriceI.toString()
        editSNum.text = editNum.toString()
        editSDes.text = editDes
        //Edit our items number
        incDecNum()
        //View Model Calling
        cartViewModel = ViewModelProvider(this)[CartViewModel::class.java]
        //Update Cart listener
        editSUpdate.setOnClickListener {
            lifecycleScope.launch {
                updateDatabase()
                Toast.makeText(context, "Item is updated", Toast.LENGTH_SHORT).show()
            }
        }
    }
    //Add data to database
    private suspend fun updateDatabase(){
        val cartedTitle = editSTitle.text.toString()
        val cartedImage = getBitmap(editImage)
        val cartedPrice = editSLPrice.text.toString().toDouble()
        val cartedPriceI = editSIPrice.text.toString().toDouble()
        val cartedItemNum = editSNum.text.toString().toInt()
        val cartedDes = editSDes.text.toString()
        val item = MyCartItemsDatabase(editPos!!, cartedTitle, cartedImage,
            cartedPrice, cartedPriceI, cartedItemNum, cartedDes)
        cartViewModel.updateCart(item)
    }
    //Converting image url to bitMap
    private suspend fun getBitmap(img: String): Bitmap {
        val loading = ImageLoader(requireContext())
        val request = ImageRequest.Builder(requireContext())
            .data(img).build()
        val result: Drawable = (loading.execute(request) as SuccessResult).drawable
        return (result as BitmapDrawable).bitmap
    }

    //Increase or decrease items' number
    private fun incDecNum(){
        //Initializing the price value
        val myPrice = editSLPrice.text.toString().toDouble()
        //Initializing the incDec value
        var numberOfItems = editSNum.text.toString().toInt()
        editSDec.setOnClickListener {
            if (numberOfItems > 1){
                numberOfItems -= 1
                val newVal = numberOfItems.toString()
                editSNum.text = newVal
                val price = myPrice*numberOfItems
                editSIPrice.text = price.toString()
            }
        }
        editSInc.setOnClickListener {
            numberOfItems += 1
            val newVal = numberOfItems.toString()
            editSNum.text = newVal
            val price = myPrice*numberOfItems
            editSIPrice.text = price.toString()
        }
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_edit_single_item, container, false)
    }

    companion object {
        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment EditSingleItemFragment.
         */
        // TODO: Rename and change types and number of parameters
        @JvmStatic
        fun newInstance(param1: String, param2: String) =
            EditSingleItemFragment().apply {
                arguments = Bundle().apply {
                    putString(ARG_PARAM1, param1)
                    putString(ARG_PARAM2, param2)
                }
            }
    }
}

我正在尝试更新在 recyclerView 中查看的我的房间数据库列。

Answer 1

我将从一些可以帮助您解决问题的建议开始，您的代码将变得非常易于理解和执行。

1. 将变量 myCartItems 从 Fragment 移动到 ViewModel 。 ViewModel 是保存状态和您在 UI 上使用的所有数据的正确位置。

2. 使用 LiveData观察 myCartItems 列表上的变化。 不要忘记保护您的财产，请遵循以下模式：

class MyViewModel: ViewModel() {

    private val _myCartItems = MutableLiveData<List<MyCartItemsDatabase>>(emptyList())
    val myCartItems: LiveData<List<MyCartItemsDatabase>>
        get() = _myCartItems

}

3. 观察 fragment 上 myCartItems 的变化。 当 myCartItems 在 ViewModel 上更新时，观察者将收到通知，然后您可以将您在观察者上收到的更新列表发送到适配器

class MyFragment: Fragment()  {

    private val viewModel: MyViewModel by viewModel()

    private lateinit var adapter: MyAdapter

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

        // set the adapter to your recycler view
        // observe changes of your live data
        viewModel.myCartItems.observe(viewLifecycleOwner) { myCartItems ->
            // You will send the myCartItems that you receive to your adapter here
        }
    }
}

4. 你在使用 RecyclerView 吗？ 更喜欢始终使用 RecyclerView而不是 ListView 或 GridView，因为它的性能要好得多。

5. 对于 Adapter 实现，总是更喜欢使用 ListAdapter ，它有一种更有效的方法来比较当前列表和新列表并更新它。 你可以按照这个例子：

abstract class MyAdapter: ListAdapter<MyCartItemsDatabase, MyAdapter.MyAdapterViewHolder>(DIFF_CALLBACK) {
   
     // ...

    class MyAdapterViewHolder(
        private val binding: ItemSimplePosterBinding
    ): RecyclerView.ViewHolder(binding.root) {
     // ...
     }

    companion object {
        private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<MyCartItemsDatabase>() {
            override fun areItemsTheSame(oldItem: MyCartItemsDatabase, newItem: MyCartItemsDatabase): Boolean {
                // need a unique identifier to have sure they are the same item. could be a comparison of ids. In this case, that is just a list of strings just compare like this below
                return oldItem.id == newItem.id
            }

            override fun areContentsTheSame(oldItem: MyCartItemsDatabase, newItem: MyCartItemsDatabase): Boolean {
                // compare the objects
                return oldItem.items == newItem.items
            }

        }
    }
}