1.前言

2.工具類要點(diǎn)

2.1 聲明并初始化AsyncListDiffer

private val mDiffer: AsyncListDiffer<T> 

2.2 創(chuàng)建DiffUtil.ItemCallback<T>，實(shí)現(xiàn)抽象方法

abstract fun areItemsTheSame(oldItem: T, newItem: T): Boolean
abstract fun areContentsTheSame(oldItem: T, newItem: T): Boolean

2.3 更新數(shù)據(jù)

fun setData(list: MutableList<T>?) {
    val newList: MutableList<T> = ArrayList()
    newList.addAll(list ?: ArrayList())
    mDiffer.submitList(newList) // 更新數(shù)據(jù)(setData()+notify())
}

3. 注意事項(xiàng)

3.1 不能重復(fù)提交同一個(gè)列表

• 更新數(shù)據(jù)前(調(diào)用submitList(List<T> newList))，請(qǐng)勿對(duì)"已被設(shè)置進(jìn)DiffUtil的list數(shù)據(jù)"進(jìn)行操作。
• 需重新創(chuàng)建list，以便DiffUtil進(jìn)行兩個(gè)新舊列表間對(duì)比。如舉例。

3.2 錯(cuò)誤示范

mData.add(...)
mAdapter.submitList(mData)

3.3 引發(fā)此問題原因

public class AsyncListDiffer<T> {
    // 更新數(shù)據(jù)
    public void submitList(@Nullable final List<T> newList, @Nullable final Runnable commitCallback) {
        // incrementing generation means any currently-running diffs are discarded when they finish
        final int runGeneration = ++mMaxScheduledGeneration;
        if (newList == mList) { // 此處進(jìn)行了過濾
            // nothing to do (Note - still had to inc generation, since may have ongoing work)
            if (commitCallback != null) {
                commitCallback.run();
            }
            return;
        }
        ...
    }
}

4. 基類封裝實(shí)現(xiàn)

使用DiffUtil進(jìn)行RecyclerView數(shù)據(jù)的對(duì)比&刷新，把相關(guān)api進(jìn)行二次封裝，以便為了更簡單調(diào)用。

4.1 BaseRecyclerDifferItemCallBack

• 對(duì)DiffUtil.ItemCallback<T>進(jìn)行二次封裝。
• RecyclerView的dapter作為參數(shù)，把對(duì)比函數(shù)回調(diào)到Adapter進(jìn)行實(shí)現(xiàn)。

class BaseRecyclerDifferItemCallBack<T>(adapter: BaseRecyclerDifferAdapter<T>?) :
        DiffUtil.ItemCallback<T>() {

    private var mAdapter: BaseRecyclerDifferAdapter<T>? = adapter

    override fun areItemsTheSame(oldItem: T, newItem: T): Boolean {
        return mAdapter?.areItemsTheSame(oldItem, newItem)?: false
    }

    override fun areContentsTheSame(oldItem: T, newItem: T): Boolean {
        return mAdapter?.areContentsTheSame(oldItem, newItem)?: false
    }
}

4.2 BaseRecyclerDifferAdapter

• 對(duì)RecyclerView.Adapter進(jìn)行二次封裝，初始化AsyncListDiffer變量用于數(shù)據(jù)操作。
• 創(chuàng)建數(shù)據(jù)對(duì)比抽象方法，用于此Adapter子類實(shí)現(xiàn)

abstract class BaseRecyclerDifferAdapter<T> : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    private val mDiffer: AsyncListDiffer<T> by lazy {
        // 數(shù)據(jù)的操作由AsyncListDiffer實(shí)現(xiàn)
        AsyncListDiffer(this, BaseRecyclerDifferItemCallBack<T>(this))
    }

    fun getCurrentData(): MutableList<T> {
        return mDiffer.currentList
    }

    /**
     * 設(shè)置數(shù)據(jù)
     * @param list MutableList<T>?
     */
    fun setData(list: MutableList<T>?){
        val newList: MutableList<T> = ArrayList()
        newList.addAll(list?: ArrayList())
        mDiffer.submitList(newList)
    }


    /**
     * 添加數(shù)據(jù)
     * @param beans Array<out T>
     */
    fun addData(vararg beans: T) {
        val newList: MutableList<T> = ArrayList()
        newList.addAll(mDiffer.currentList)
        beans.forEach { bean ->
            newList.add(bean)
        }
        mDiffer.submitList(newList)
    }

    /**
     * 加載更多
     * @param list MutableList<T>?
     */
    fun loadMore(list: MutableList<T>?){
        val newList: MutableList<T> = ArrayList()
        newList.addAll(mDiffer.currentList)
        newList.addAll(list?: ArrayList())
        mDiffer.submitList(newList)
    }

    /**
     * 刪除數(shù)據(jù)
     * @param index Int
     */
    fun removeData(index: Int) {
        val newList: MutableList<T> = ArrayList()
        val currentList = mDiffer.currentList
        if (currentList.isNotEmpty() && index in 0 until currentList.size) {
            newList.addAll(currentList)
            newList.removeAt(index)
            mDiffer.submitList(newList)
        }
    }

    /**
     * 清空數(shù)據(jù)
     */
    fun clear() {
        mDiffer.submitList(null)
    }

    abstract fun areItemsTheSame(oldItem: T, newItem: T): Boolean
    abstract fun areContentsTheSame(oldItem: T, newItem: T): Boolean

4.2 業(yè)務(wù)Adapter實(shí)現(xiàn)

• 舉例說明BaseRecyclerDifferAdapter使用方式
• 以下為偽代碼，僅包含關(guān)鍵實(shí)現(xiàn)

class RVDifferAdapter(context: Context) : BaseRecyclerDifferAdapter<RVDifferBean>() {
    
    private var mContext: Context = context

    /**
     * Item對(duì)比
     */
    override fun areItemsTheSame(oldItem: RVDifferBean, newItem: RVDifferBean): Boolean {
        return oldItem.id == newItem.id // 比較邏輯自行實(shí)現(xiàn)
    }
    
    /**
     * Content對(duì)比
     */
    override fun areContentsTheSame(oldItem: RVDifferBean, newItem: RVDifferBean): Boolean {
        return oldItem.name == newItem.name // 比較邏輯自行實(shí)現(xiàn)
    }

    private var mInflater: LayoutInflater = LayoutInflater.from(context)

    /**
     * 獲取單條item數(shù)據(jù)
     *
     * @param position
     * @return
     */
    private fun getItemAtPosition(position: Int): RVDifferBean? {
        val itemCount: Int = itemCount
        return if (itemCount != 0 && position in 0 until itemCount) {
            getCurrentData()[position]
        } else {
            null
        }
    }

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

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {}

    override fun onBindViewHolder(
        holder: RecyclerView.ViewHolder,
        position: Int,
        payloads: MutableList<Any>
    ) {
        super.onBindViewHolder(holder, position, payloads)
    }

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

參考文檔：

官方文檔地址：[https://developer.android.google.cn/reference/kotlin/androidx/recyclerview/widget/DiffUtil]