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RecyclerView position helper to get first and last visible positions
/**
* Custom Scroll listener for RecyclerView.
* Based on implementation https://gist.github.com/ssinss/e06f12ef66c51252563e
*/
public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener {
public static String TAG = "EndlessScrollListener";
private int previousTotal = 0; // The total number of items in the dataset after the last load
private boolean loading = true; // True if we are still waiting for the last set of data to load.
private int visibleThreshold = 5; // The minimum amount of items to have below your current scroll position before loading more.
int firstVisibleItem, visibleItemCount, totalItemCount;
private int currentPage = 1;
RecyclerViewPositionHelper mRecyclerViewHelper;
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
mRecyclerViewHelper = RecyclerViewPositionHelper.createHelper(recyclerView);
visibleItemCount = recyclerView.getChildCount();
totalItemCount = mRecyclerViewHelper.getItemCount();
firstVisibleItem = mRecyclerViewHelper.findFirstVisibleItemPosition();
if (loading) {
if (totalItemCount > previousTotal) {
loading = false;
previousTotal = totalItemCount;
}
}
if (!loading && (totalItemCount - visibleItemCount)
<= (firstVisibleItem + visibleThreshold)) {
// End has been reached
// Do something
currentPage++;
onLoadMore(currentPage);
loading = true;
}
}
//Start loading
public abstract void onLoadMore(int currentPage);
}
/**
* RecyclerView position helper class for any LayoutManager.
*
* compile 'com.android.support:recyclerview-v7:22.0.0'
*/
import android.support.v7.widget.OrientationHelper;
import android.support.v7.widget.RecyclerView;
import android.view.View;
public class RecyclerViewPositionHelper {
final RecyclerView recyclerView;
final RecyclerView.LayoutManager layoutManager;
RecyclerViewPositionHelper(RecyclerView recyclerView) {
this.recyclerView = recyclerView;
this.layoutManager = recyclerView.getLayoutManager();
}
public static RecyclerViewPositionHelper createHelper(RecyclerView recyclerView) {
if (recyclerView == null) {
throw new NullPointerException("Recycler View is null");
}
return new RecyclerViewPositionHelper(recyclerView);
}
/**
* Returns the adapter item count.
*
* @return The total number on items in a layout manager
*/
public int getItemCount() {
return layoutManager == null ? 0 : layoutManager.getItemCount();
}
/**
* Returns the adapter position of the first visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
*
* @return The adapter position of the first visible item or {@link RecyclerView#NO_POSITION} if
* there aren't any visible items.
*/
public int findFirstVisibleItemPosition() {
final View child = findOneVisibleChild(0, layoutManager.getChildCount(), false, true);
return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
}
/**
* Returns the adapter position of the first fully visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
*
* @return The adapter position of the first fully visible item or
* {@link RecyclerView#NO_POSITION} if there aren't any visible items.
*/
public int findFirstCompletelyVisibleItemPosition() {
final View child = findOneVisibleChild(0, layoutManager.getChildCount(), true, false);
return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
}
/**
* Returns the adapter position of the last visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
*
* @return The adapter position of the last visible view or {@link RecyclerView#NO_POSITION} if
* there aren't any visible items
*/
public int findLastVisibleItemPosition() {
final View child = findOneVisibleChild(layoutManager.getChildCount() - 1, -1, false, true);
return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
}
/**
* Returns the adapter position of the last fully visible view. This position does not include
* adapter changes that were dispatched after the last layout pass.
*
* @return The adapter position of the last fully visible view or
* {@link RecyclerView#NO_POSITION} if there aren't any visible items.
*/
public int findLastCompletelyVisibleItemPosition() {
final View child = findOneVisibleChild(layoutManager.getChildCount() - 1, -1, true, false);
return child == null ? RecyclerView.NO_POSITION : recyclerView.getChildAdapterPosition(child);
}
View findOneVisibleChild(int fromIndex, int toIndex, boolean completelyVisible,
boolean acceptPartiallyVisible) {
OrientationHelper helper;
if (layoutManager.canScrollVertically()) {
helper = OrientationHelper.createVerticalHelper(layoutManager);
} else {
helper = OrientationHelper.createHorizontalHelper(layoutManager);
}
final int start = helper.getStartAfterPadding();
final int end = helper.getEndAfterPadding();
final int next = toIndex > fromIndex ? 1 : -1;
View partiallyVisible = null;
for (int i = fromIndex; i != toIndex; i += next) {
final View child = layoutManager.getChildAt(i);
final int childStart = helper.getDecoratedStart(child);
final int childEnd = helper.getDecoratedEnd(child);
if (childStart < end && childEnd > start) {
if (completelyVisible) {
if (childStart >= start && childEnd <= end) {
return child;
} else if (acceptPartiallyVisible && partiallyVisible == null) {
partiallyVisible = child;
}
} else {
return child;
}
}
}
return partiallyVisible;
}
}
@carlonzo

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carlonzo commented Apr 10, 2017

why are you creating an helper while you scroll? https://gist.github.com/mustafasevgi/7dcb18166aaf9944e6450ec2878a646a#file-endlessrecycleronscrolllistener-java-L20

allocating a new objects while you scroll is a very bad approach.

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