Android RecyclerView page/paging load,kotlin（3）

布满荆棘的人生 2023-10-10 19:05 42阅读 0赞

Android GridLayoutManager RecyclerView page load/paging load，by calculate screen position from already loaded item's position，kotlin（3）

package my.application
    
    import android.os.Bundle
    import android.util.Log
    import androidx.appcompat.app.AppCompatActivity
    import androidx.recyclerview.widget.GridLayoutManager
    import androidx.recyclerview.widget.RecyclerView
    import androidx.recyclerview.widget.RecyclerView.OnScrollListener
    
    class MainActivity : AppCompatActivity() {
        companion object {
            val TAG = "fly"
        }
    
        val PAGE_SIZE = 50 //每一页的数据总数
        var PAGE_COUNT = 0 //记录已经加载的页数
    
        val mAdapter = MyAdapter()
    
        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
    
            val recyclerView = findViewById<RecyclerView>(R.id.recycler_view)
            recyclerView.layoutManager = GridLayoutManager(this, 4).apply {
                orientation = GridLayoutManager.VERTICAL
            }
    
            //假设已经知道全量数据，后续的分段是把源数据一片一片的截出来，装到新的分页数据集里面
            val ITEMS = ArrayList<MyData>()
            for (i in 0..1000) {
                var data = MyData("$i", "@$i")
                ITEMS.add(data)
            }
    
            recyclerView.adapter = mAdapter
    
            var mIsLoading = false
            var rang = IntArray(2) { 0 }
            recyclerView.addOnScrollListener(object : OnScrollListener() {
                override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                    if (mIsLoading) {
                        Log.d(TAG, "正在加载!")
                        return
                    }
    
                    getOutRange(recyclerView, rang)
    
                    var pos = ITEMS.size - PAGE_SIZE * PAGE_COUNT
                    Log.d(TAG, "onScrolled ${rang[0]}->${rang[1]} $pos")
                    if (rang[0] - pos < PAGE_SIZE) {
                        mIsLoading = true
    
                        PAGE_COUNT++
    
                        Log.d(TAG, "load $PAGE_COUNT ->")
                        paging(ITEMS, PAGE_SIZE, PAGE_COUNT)
                        Log.d(TAG, "load $PAGE_COUNT <-")
    
                        mIsLoading = false
                    }
                }
            })
    
            PAGE_COUNT = 1
            paging(ITEMS, PAGE_SIZE, PAGE_COUNT)
    
            //recyclerView启动后默认滚到最底部
            recyclerView.scrollToPosition(mAdapter.getItemCount() - 1)
        }
    
        fun paging(
            sourceItems: ArrayList<MyData>,
            pageSize: Int,
            pageCount: Int
        ) {
            Log.d(TAG, "加载第 $pageCount 页")
    
            //新的分页数据集
            var pageItems: ArrayList<MyData>? = ArrayList()
    
            var count = pageCount * pageSize
            if (count > sourceItems.size) {
                //因为分页是基于整数PAGE_SIZE分页的，很可能PAGE_SIZE * PAGE_COUNT大于实际sourceItems长度
                pageItems = sourceItems.toList() as ArrayList<MyData>
            } else {
                var pos = sourceItems.size - pageSize * pageCount
                for (i in 0 until pos) {
                    //上部分加入占位数据
                    pageItems?.add(MyData("-1", "-1"))
                }
    
                for (i in 0 until count) {
                    //截取真实的源数据到新的分页数据items里面
                    pageItems?.add(sourceItems.get(pos + i)!!)
                }
            }
    
            mAdapter.onChange(pageItems!!)
        }
    
        fun getOutRange(rv: RecyclerView, outRange: IntArray) {
            outRange[0] = (rv.layoutManager as GridLayoutManager?)!!.findFirstVisibleItemPosition()
            outRange[1] = (rv.layoutManager as GridLayoutManager?)!!.findLastVisibleItemPosition()
        }
    }

<?xml version="1.0" encoding="utf-8"?>
    <androidx.recyclerview.widget.RecyclerView xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity" />

package my.application
    
    import android.view.LayoutInflater
    import android.view.View
    import android.view.ViewGroup
    import android.widget.TextView
    import androidx.recyclerview.widget.RecyclerView
    
    class MyAdapter() : RecyclerView.Adapter<MyViewHolder>() {
        var items: ArrayList<MyData>? = ArrayList()
    
        fun onChange(items: ArrayList<MyData>) {
            this.items?.clear()
    
            this.items = items
    
            this.notifyDataSetChanged()
        }
    
        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
            val view = LayoutInflater.from(parent.context)
                .inflate(android.R.layout.simple_list_item_2, parent, false)
            return MyViewHolder(view)
        }
    
        override fun getItemCount(): Int {
            return items?.size!!
        }
    
        override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
            holder.name.text = items?.get(position)?.name
            holder.desc.text = items?.get(position)?.desc
        }
    }
    
    class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val name: TextView = itemView.findViewById(android.R.id.text1)
        val desc: TextView = itemView.findViewById(android.R.id.text2)
    }
    
    data class MyData(var name: String, var desc: String)

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