当数据库中的单个数据更改时，RecyclerView会设置所有项目

问题描述

我正在使用LiveData这样从数据库中获取30个项目：

@Query("SELECT * FROM table ORDER BY id DESC LIMIT 30")
fun getLast30(): LiveData<List<Person>>

每个回收站视图项都有一个“喜欢”按钮，并且适配器中有一个接口：

interface OnItemClickedAdapter {
    fun onFavButtonClicked(position: Int)
}

结束，单击“赞”按钮时，我正在更新数据库中的单个项目。当我使用LiveData时，它正在获取更新的30个项目。我正在使用观察方法：

设置数据

 viewModel.last30.observe(viewLifecycleOwner,{
      adapter.submitList(it)
 }

问题：

• 单击“喜欢”按钮时，“回收者”视图将刷新其所有内容，并滚动到第一项。

已编辑： SubmitList（list：List）方法：

fun submitList(persons: List<Person>) {
    val diffResult: DiffUtil.DiffResult = DiffUtil.calculateDiff(
        ApodGalleryAdapterDiffCallback(
            this.persons,persons
        )
    )
    this.persons = person
    diffResult.dispatchUpdatesTo(this)
}

DiffUtill类：

class PersonAdapterDiffCallback(var oldList: List<Person>,var newList: List<Person>) :
    DiffUtil.Callback() {

    override fun getOldListSize(): Int {
        return oldList.size
    }

    override fun getNewListSize(): Int {
        return newList.size
    }

    override fun areItemsTheSame(oldItemPosition: Int,newItemPosition: Int): Boolean {
        return oldList[oldItemPosition].url == newList[newItemPosition].url
    }

    override fun areContentsTheSame(oldItemPosition: Int,newItemPosition: Int): Boolean {
        return oldList[oldItemPosition] == newList[newItemPosition]
    }

}

适配器类：

class ApodGalleryAdapter() :
    RecyclerView.Adapter<ApodGalleryAdapter.ApodGalleryViewHolder>() {

    var onItemClickedGalleryAdapter: OnItemClickedGalleryAdapter? = null

    override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): ApodGalleryViewHolder {
        return ApodGalleryViewHolder(
            LayoutInflater.from(parent.context).inflate(R.layout.item_apod_gallery,parent,false),onItemClickedGalleryAdapter
        )
    }

    private var apods: List<Apod> = ArrayList()

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

    override fun onBindViewHolder(holder: ApodGalleryViewHolder,position: Int) {
        holder.bindData(apods[position],position)
    }

    fun submitList(apods: List<Apod>) {

        val diffResult: DiffUtil.DiffResult = DiffUtil.calculateDiff(
            ApodGalleryAdapterDiffCallback(
                this.apods,apods
            )
        )

        this.apods = apods

        diffResult.dispatchUpdatesTo(this)
    }

    class ApodGalleryViewHolder(
        itemView: View,var onItemClickedGalleryAdapter: OnItemClickedGalleryAdapter?
    ) :
        RecyclerView.ViewHolder(itemView) {
        private val apodImage: ImageView = itemView.image_item_apod
        private val apodTitle: TextView = itemView.title_item_apod
        private val apodDescription: TextView = itemView.description_item_apod
        private val apodCopyright: TextView = itemView.copyright_item_apod

        fun bindData(apod: Apod,position: Int) {
            when {
                apod.url.endsWith(".jpg") -> {
                    Glide.with(apodImage.context)
                        .load(apod.url)
                        .placeholder(R.drawable.transparent)
                        .into(apodImage)
                }
                apod.url.contains("youtube") -> {
                    Glide.with(apodImage.context)
                        .load(getThumbnailUrl(apod.url))
                        .placeholder(R.drawable.transparent)
                        .into(apodImage)
                }
                else -> {
                    apodImage.setImageResource(R.drawable.transparent)
                }
            }
            apodTitle.text = apod.title
            apodDescription.text = apod.explanation
            apodCopyright.text = apod.copyright

            if (apod.isLiked) {
                itemView.fav_button_item_apod_gallery.setImageResource(R.drawable.ic_round_favorite_24)
            } else {
                itemView.fav_button_item_apod_gallery.setImageResource(R.drawable.ic_round_favorite_border_24)
            }

            itemView.setOnClickListener {
                onItemClickedGalleryAdapter?.onClick(apod.date)
            }
            itemView.fav_button_item_apod_gallery.setOnClickListener {
                onItemClickedGalleryAdapter?.onFavButtonClicked(position)
            }

        }
    }
}

interface OnItemClickedGalleryAdapter {

    fun onClick(date: String)

    fun onFavButtonClicked(position: Int)
}

class ApodGalleryAdapterDiffCallback(var oldList: List<Apod>,var newList: List<Apod>) :
    DiffUtil.Callback() {

    override fun getOldListSize(): Int {
        return oldList.size
    }

    override fun getNewListSize(): Int {
        return newList.size
    }

    override fun areItemsTheSame(oldItemPosition: Int,newItemPosition: Int): Boolean {
        return oldList[oldItemPosition] == newList[newItemPosition]
    }

}

我已经覆盖了Data类的equals()方法：

override fun equals(other: Any?): Boolean {

    if (javaClass != other?.javaClass)
        return false

    other as Apod

    if (id != other.id)
        return false

    if (copyright != other.copyright)
        return false

    if (date != other.date)
        return false

    if (explanation != other.explanation)
        return false

    if (hdUrl != other.hdUrl)
        return false

    if (media_type != other.media_type)
        return false

    if (service_version != other.service_version)
        return false

    if (url != other.url)
        return false

    if (isLiked != other.isLiked)
        return false

    return true
}

解决方法

在DiffUtil实现中，areContentsTheSame始终返回false。

override fun areContentsTheSame(oldItemPosition: Int,newItemPosition: Int): Boolean {
    return oldList[oldItemPosition] == newList[newItemPosition] // always returns false
}

您必须像这样检查每个变量：

//for example
data class Person(
    val name:String,val age:Int
)

override fun areContentsTheSame(oldItemPosition: Int,newItemPosition: Int): Boolean {
    val oldItem = oldList[oldItemPosition]
    val newItem = newList[newItemPosition]

    return oldItem.name.equals(newItem.name) && 
               oldItem.age == newItem.age
}

,

我非常了解 liveData ， DiffUtill 和adapter.notifyItemChanged(position)

真正的问题在我的观察者栏中：

    viewModel.apod30Days.observe(viewLifecycleOwner,{
        adapter.submitList(it)
        adapter.onItemClickedGalleryAdapter = object : OnItemClickedGalleryAdapter {
            override fun onClick(date: String) {
                val intent =
                    Intent(requireActivity().applicationContext,DetailsActivity::class.java)
                intent.putExtra(DetailsActivity.APOD_DATE_KEY,date)
                startActivity(intent)
            }

            override fun onFavButtonClicked(position: Int) {
                val apod = it[position]
                apod.isLiked = !apod.isLiked
                viewModel.updateApod(apod)
                adapter.notifyItemChanged(position)
            }
        }
        if (it.size < 30)
            viewModel.setLast30Apods()
        binding.apodViewPager.adapter = adapter
    })

在此块的最后一行，当liveData更改时，我一次又一次地设置适配器。 DiffUtill运行得很好。