EndlessRecyclerScrollListener.java
package br.com.catbag.gifreduxsample.ui;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
/**
at https://gist.github.com/nesquena/d09dc68ff07e845cc622
Credits from this gist to https://gist.github.com/nesquena and https://gist.github.com/rogerhu
**/
public abstract class EndlessRecyclerScrollListener extends RecyclerView.OnScrollListener {
// The minimum amount of items to have below your current scroll position
// before mLoading more.
private int mVisibleThreshold = 5;
// The current offset index of data you have loaded
private int mCurrentPage = 0;
// The total number of items in the dataset after the last load
private int mPreviousTotalItemCount = 0;
// True if we are still waiting for the last set of data to load.
private boolean mLoading = true;
// Sets the starting page index
private int mStartingPageIndex = 0;
private RecyclerView.LayoutManager mLayoutManager;
public EndlessRecyclerScrollListener(LinearLayoutManager layoutManager) {
mLayoutManager = layoutManager;
}
public EndlessRecyclerScrollListener(GridLayoutManager layoutManager) {
mLayoutManager = layoutManager;
mVisibleThreshold = mVisibleThreshold * layoutManager.getSpanCount();
}
public EndlessRecyclerScrollListener(StaggeredGridLayoutManager layoutManager) {
mLayoutManager = layoutManager;
mVisibleThreshold = mVisibleThreshold * layoutManager.getSpanCount();
}
public 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 < mPreviousTotalItemCount) {
mCurrentPage = mStartingPageIndex;
mPreviousTotalItemCount = totalItemCount;
if (totalItemCount == 0) {
mLoading = true;
}
}
// If it’s still mLoading, we check to see if the dataset count has
// changed, if so we conclude it has finished mLoading and update the current page
// number and total item count.
if (mLoading && (totalItemCount > mPreviousTotalItemCount)) {
mLoading = false;
mPreviousTotalItemCount = totalItemCount;
}
// If it isn’t currently mLoading, we check to see if we have breached
// the mVisibleThreshold 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 (!mLoading && (lastVisibleItemPosition + mVisibleThreshold) > totalItemCount) {
mCurrentPage++;
onLoadMore(mCurrentPage, totalItemCount, view);
mLoading = true;
}
}
// Call this method whenever performing new searches
public void resetState() {
mCurrentPage = mStartingPageIndex;
mPreviousTotalItemCount = 0;
mLoading = true;
}
// Defines the process for actually mLoading more data based on page
public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);
}