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Endless RecyclerView scroll listener for simple pagination in Android.
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// TODO: put package information here | |
import android.support.v7.widget.GridLayoutManager; | |
import android.support.v7.widget.LinearLayoutManager; | |
import android.support.v7.widget.RecyclerView; | |
import android.support.v7.widget.StaggeredGridLayoutManager; | |
import org.jetbrains.annotations.Contract; | |
/** | |
* | |
* Created by Prem $ on 11/14/2017. | |
*/ | |
public abstract class EndlessRecyclerViewScrollListener extends RecyclerView.OnScrollListener { | |
// The minimum amount of items to have below your current scroll position | |
// before loading more. | |
private int visibleThreshold = 8; | |
// The current offset index of data you have loaded | |
private int currentPage = 1; | |
// The total number of items in the data set after the last load | |
private int previousTotalItemCount = 0; | |
// True if we are still waiting for the last set of data to load. | |
private boolean loading = true; | |
// Sets the starting page index | |
private int startingPageIndex = 1; | |
private RecyclerView.LayoutManager mLayoutManager; | |
protected EndlessRecyclerViewScrollListener(LinearLayoutManager layoutManager) { | |
this.mLayoutManager = layoutManager; | |
loadFirstPage(); | |
} | |
protected EndlessRecyclerViewScrollListener(GridLayoutManager layoutManager) { | |
this.mLayoutManager = layoutManager; | |
visibleThreshold = visibleThreshold * layoutManager.getSpanCount(); | |
} | |
protected EndlessRecyclerViewScrollListener(StaggeredGridLayoutManager layoutManager) { | |
this.mLayoutManager = layoutManager; | |
visibleThreshold = visibleThreshold * layoutManager.getSpanCount(); | |
loadFirstPage(); | |
} | |
@Contract(pure = true) | |
private int getLastVisibleItem(int[] lastVisibleItemPositions) { | |
int maxSize = 0; | |
for (int i = 0; i < lastVisibleItemPositions.length; i++) { | |
if (i == 0) { | |
maxSize = lastVisibleItemPositions[i]; | |
} | |
else if (lastVisibleItemPositions[i] > maxSize) { | |
maxSize = lastVisibleItemPositions[i]; | |
} | |
} | |
return maxSize; | |
} | |
// 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 | |
public void onScrolled(RecyclerView view, int dx, int dy) { | |
int lastVisibleItemPosition = 0; | |
int totalItemCount = mLayoutManager.getItemCount(); | |
if (mLayoutManager instanceof StaggeredGridLayoutManager) { | |
int[] lastVisibleItemPositions = ((StaggeredGridLayoutManager) mLayoutManager).findLastVisibleItemPositions(null); | |
// get maximum element within the list | |
lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions); | |
} else if (mLayoutManager instanceof GridLayoutManager) { | |
lastVisibleItemPosition = ((GridLayoutManager) mLayoutManager).findLastVisibleItemPosition(); | |
} else if (mLayoutManager instanceof LinearLayoutManager) { | |
lastVisibleItemPosition = ((LinearLayoutManager) mLayoutManager).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) { | |
this.currentPage = this.startingPageIndex; | |
this.previousTotalItemCount = totalItemCount; | |
if (totalItemCount == 0) { | |
this.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; | |
previousTotalItemCount = totalItemCount; | |
} | |
// 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 | |
public void resetState() { | |
this.currentPage = this.startingPageIndex; | |
this.previousTotalItemCount = 0; | |
this.loading = true; | |
} | |
// Defines the process for loading the first page | |
public void loadFirstPage(){} | |
// Defines the process for actually loading more data based on page | |
public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view); | |
} |
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