Created
November 7, 2022 10:52
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Helper class for pagination
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package com.rex50.mausam.utils | |
import androidx.recyclerview.widget.GridLayoutManager | |
import androidx.recyclerview.widget.LinearLayoutManager | |
import androidx.recyclerview.widget.RecyclerView | |
import androidx.recyclerview.widget.StaggeredGridLayoutManager | |
/* | |
* Usage in Kotlin | |
* addOnScrollListener(object: EndlessRecyclerOnScrollListener(layoutManager){ | |
* override fun onLoadMore(page: Int, totalItemsCount: Int, view: RecyclerView?) { | |
* viewModel.getPhotosOf(page) | |
* } | |
* }.also { | |
* it.setInitialPage(INITIAL_PAGE) | |
* it.setVisibleThreshold(4) | |
* it.setVisibleThreshold(4) | |
* }) | |
*/ | |
abstract class EndlessRecyclerOnScrollListener : RecyclerView.OnScrollListener { | |
// The minimum amount of items to have below your current scroll position | |
// before loading more. | |
private var visibleThreshold = 5 | |
// The current offset index of data you have loaded | |
private var currentPage = 1 | |
// The total number of items in the dataset after the last load | |
private var previousTotalItemCount = 0 | |
private var lastPreviousTotalItemCount = previousTotalItemCount | |
// True if we are still waiting for the last set of data to load. | |
private var loading = true | |
// Sets the starting page index | |
private var startingPageIndex = 1 | |
// Sets how many elements will be added each time. | |
private var loadItemFreq = 20 | |
private var mLayoutManager: RecyclerView.LayoutManager? = null | |
private constructor() | |
constructor(layoutManager: LinearLayoutManager?) { | |
mLayoutManager = layoutManager | |
} | |
constructor(layoutManager: GridLayoutManager) { | |
mLayoutManager = layoutManager | |
visibleThreshold *= layoutManager.spanCount | |
} | |
constructor(layoutManager: StaggeredGridLayoutManager) { | |
mLayoutManager = layoutManager | |
visibleThreshold *= layoutManager.spanCount | |
} | |
fun getLastVisibleItem(lastVisibleItemPositions: IntArray): Int { | |
var maxSize = 0 | |
for (i in lastVisibleItemPositions.indices) { | |
if (i == 0) { | |
maxSize = lastVisibleItemPositions[i] | |
} else if (lastVisibleItemPositions[i] > maxSize) { | |
maxSize = lastVisibleItemPositions[i] | |
} | |
} | |
return maxSize | |
} | |
//Call this method if last list request failed | |
fun lastRequestFailed() { | |
currentPage-- | |
previousTotalItemCount = lastPreviousTotalItemCount | |
} | |
//Call this method to set visible threshold | |
fun setVisibleThreshold(threshold: Int) { | |
visibleThreshold = threshold | |
} | |
//call this method to set numbers of items will loaded at once | |
open fun setLoadItemsFrequency(loadItemFreq: Int) { | |
this.loadItemFreq = loadItemFreq | |
} | |
// This happens many times a second during a scroll, so be wary of the code you place here. | |
// We are given a few useful parameters to help us work out if we need to load some more data, | |
// but first we check if we are waiting for the previous load to finish. | |
override fun onScrolled(view: RecyclerView, dx: Int, dy: Int) { | |
var lastVisibleItemPosition = 0 | |
val totalItemCount = mLayoutManager!!.itemCount | |
if (mLayoutManager is StaggeredGridLayoutManager) { | |
val lastVisibleItemPositions = (mLayoutManager as StaggeredGridLayoutManager).findLastVisibleItemPositions(null) | |
// get maximum element within the list | |
lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions) | |
} else if (mLayoutManager is GridLayoutManager) { | |
lastVisibleItemPosition = (mLayoutManager as GridLayoutManager).findLastVisibleItemPosition() | |
} else if (mLayoutManager is LinearLayoutManager) { | |
lastVisibleItemPosition = (mLayoutManager as LinearLayoutManager).findLastVisibleItemPosition() | |
} | |
// If the total item count is zero and the previous isn't, assume the | |
// list is invalidated and should be reset back to initial state | |
if (totalItemCount < previousTotalItemCount) { | |
currentPage = startingPageIndex | |
previousTotalItemCount = totalItemCount | |
if (totalItemCount == 0) { | |
loading = true | |
} | |
} | |
// If it’s still loading, we check to see if the dataset count has | |
// changed, if so we conclude it has finished loading and update the current page | |
// number and total item count. | |
if (loading && totalItemCount > previousTotalItemCount) { | |
loading = false | |
lastPreviousTotalItemCount = previousTotalItemCount | |
previousTotalItemCount = totalItemCount | |
} | |
if(totalItemCount - lastPreviousTotalItemCount == loadItemFreq) { | |
// If it isn’t currently loading, we check to see if we have breached | |
// the visibleThreshold and need to reload more data. | |
// If we do need to reload some more data, we execute onLoadMore to fetch the data. | |
// threshold should reflect how many total columns there are too | |
if (!loading && (lastVisibleItemPosition + visibleThreshold) >= totalItemCount) { | |
currentPage++; | |
onLoadMore(currentPage, totalItemCount, view); | |
loading = true; | |
} | |
} | |
} | |
// Call this method whenever performing new searches | |
fun resetState() { | |
currentPage = startingPageIndex | |
previousTotalItemCount = 0 | |
loading = true | |
} | |
fun setInitialPage(initialPage: Int){ | |
startingPageIndex = initialPage | |
currentPage = initialPage | |
} | |
// Defines the process for actually loading more data based on page | |
abstract fun onLoadMore(page: Int, totalItemsCount: Int, view: RecyclerView?) | |
} |
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