Android Jetpack：如何使用PagingDataAdapter在回收器视图中进行多重选择？

问题描述

我想在我的Android应用中进行多项选择。 我以前做过，但是只能用ArrayAdapter。

我有一个Flow作为我的数据集，并且使用了带有ViewHolder的PagingDataAdapter。

我的问题是，如果数据集不仅是列表，而且我真的不能那么容易地访问它，该如何进行多重选择。

如果您想查找代码，请重新编码：

Fragment Adapter ViewHolder ViewModel

解决方法

我已经实现了一种自定义方式。

我在适配器中使用了一个可观察的列表，并将方法公开给视图持有者以选择他们自己。

我的代码：

Adapter

class PhotoAdapter(
    private val context: Context,private val photoRepository: PhotoRepository,private val viewPhotoCallback: KFunction1<Int,Unit>,val lifecycleOwner: LifecycleOwner
) : PagingDataAdapter<Photo,PhotoViewHolder>(differCallback) {

    /**
     * Holds the layout positions of the selected items.
     */
    val selectedItems = ObservableArrayList<Int>()

    /**
     * Holds a Boolean indicating if multi selection is enabled. In a LiveData.
     */
    var isMultiSelectMode: MutableLiveData<Boolean> = MutableLiveData(false)

    var isEmpty: MutableLiveData<Boolean> = MutableLiveData(true)

    override fun onBindViewHolder(holder: PhotoViewHolder,position: Int) {
        holder.bindTo(this,getItem(position))
    }

    override fun onCreateViewHolder(parent: ViewGroup,viewType: Int): PhotoViewHolder =
        PhotoViewHolder(parent,context,photoRepository)


    fun viewPhoto(position: Int) {
        viewPhotoCallback.invoke(getItem(position)?.id!!)
    }

    fun disableSelection() {
        selectedItems.clear()
        isMultiSelectMode.postValue(false)
    }

    fun enableSelection() {
        isMultiSelectMode.postValue(true)
    }

    fun addItemToSelection(position: Int): Boolean = selectedItems.add(position)

    fun removeItemFromSelection(position: Int) = selectedItems.remove(position)

    fun isItemSelected(position: Int) = selectedItems.contains(position)

    fun isLastSelectedItem(position: Int) = isItemSelected(position) && selectedItems.size == 1

    fun selectAll() {
        for (i in 0 until itemCount) {
            if (!isItemSelected(i)) {
                addItemToSelection(i)
            }
        }
    }

    companion object {
        /**
         * Callback to check if items differ. Needed by [PagingDataAdapter].
         */
        private val differCallback = object : DiffUtil.ItemCallback<Photo>() {

            override fun areItemsTheSame(oldItem: Photo,newItem: Photo): Boolean =
                oldItem.id == newItem.id

            override fun areContentsTheSame(oldItem: Photo,newItem: Photo): Boolean =
                oldItem == newItem

        }
    }

}

ViewHolder

class PhotoViewHolder(
    parent: ViewGroup,private val context: Context,private val photoRepository: PhotoRepository
) : RecyclerView.ViewHolder(
    LayoutInflater.from(parent.context).inflate(R.layout.photo_item,parent,false)
) {
    private val imageView: ImageView = itemView.findViewById(R.id.photoItemImageView)
    private val checkBox: CheckBox = itemView.findViewById(R.id.photoItemCheckBox)

    var photo: Photo? = null
    private lateinit var adapter: PhotoAdapter

    fun bindTo(adapter: PhotoAdapter,photo: Photo?) {
        this.photo = photo
        this.adapter = adapter
        imageView.setOnClickListener {
            if (adapter.isMultiSelectMode.value!!) {
                // If the item clicked is the last selected item
                if (adapter.isLastSelectedItem(layoutPosition)) {
                    adapter.disableSelection()
                    return@setOnClickListener
                }
                // Set checked if not already checked
                setItemChecked(!adapter.isItemSelected(layoutPosition))
            } else {
                adapter.viewPhoto(layoutPosition)
            }
        }

        imageView.setOnLongClickListener {
            if (!adapter.isMultiSelectMode.value!!) {
                adapter.enableSelection()
                setItemChecked(true)
            }
            true
        }

        adapter.isMultiSelectMode.observe(adapter.lifecycleOwner,{
            if (it) { // When selection gets enabled,show the checkbox
                checkBox.visibility = View.VISIBLE
            } else {
                checkBox.visibility = View.GONE
            }
        })

        adapter.selectedItems.addOnListChangedCallback(onSelectedItemsChanged)

        listChanged()
        loadThumbnail()
    }

    /**
     * Listener for changes in selected images.
     * Calls [listChanged] whatever happens.
     */
    private val onSelectedItemsChanged =
        object : ObservableList.OnListChangedCallback<ObservableList<Int>>() {

            // No implementation needed
            override fun onChanged(sender: ObservableList<Int>?) {
                listChanged()
            }

            override fun onItemRangeChanged(
                sender: ObservableList<Int>?,positionStart: Int,itemCount: Int
            ) {
                listChanged()
            }

            override fun onItemRangeInserted(
                sender: ObservableList<Int>?,itemCount: Int
            ) {
                listChanged()
            }

            override fun onItemRangeMoved(
                sender: ObservableList<Int>?,fromPosition: Int,toPosition: Int,itemCount: Int
            ) {
                listChanged()
            }

            override fun onItemRangeRemoved(
                sender: ObservableList<Int>?,itemCount: Int
            ) {
                listChanged()
            }

        }

    private fun listChanged() {
        checkBox.isChecked = adapter.isItemSelected(layoutPosition)
    }

    private fun setItemChecked(checked: Boolean) {
        layoutPosition.let {
            if (checked) {
                adapter.addItemToSelection(it)
            } else {
                adapter.removeItemFromSelection(it)
            }
        }
    }