PagedSnapHelper.java revision b226d4dcc396fe8837876dfa113143702dd23c26
1b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen/* 2b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Copyright (C) 2017 The Android Open Source Project 3b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 4b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Licensed under the Apache License, Version 2.0 (the "License"); 5b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * you may not use this file except in compliance with the License. 6b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * You may obtain a copy of the License at 7b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 8b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * http://www.apache.org/licenses/LICENSE-2.0 9b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 10b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Unless required by applicable law or agreed to in writing, software 11b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * distributed under the License is distributed on an "AS IS" BASIS, 12b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * See the License for the specific language governing permissions and 14b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * limitations under the License. 15b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 16b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 17b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenpackage androidx.car.widget; 18b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 19b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenimport android.support.annotation.NonNull; 20b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenimport android.support.annotation.Nullable; 21b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenimport android.support.v7.widget.LinearSnapHelper; 22b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenimport android.support.v7.widget.OrientationHelper; 23b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenimport android.support.v7.widget.RecyclerView; 24b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenimport android.view.View; 25b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 26b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen/** 27b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Extension of a {@link LinearSnapHelper} that will snap to the start of the target child view to 28b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * the start of the attached {@link RecyclerView}. The start of the view is defined as the top 29b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * if the RecyclerView is scrolling vertically; it is defined as the left (or right if RTL) if the 30b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * RecyclerView is scrolling horizontally. 31b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 32b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chenpublic class PagedSnapHelper extends LinearSnapHelper { 33b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** 34b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * The percentage of a View that needs to be completely visible for it to be a viable snap 35b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * target. 36b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 37b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private static final float VIEW_VISIBLE_THRESHOLD = 0.5f; 38b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 39b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private RecyclerView mRecyclerView; 40b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 41b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // Orientation helpers are lazily created per LayoutManager. 42b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Nullable 43b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private OrientationHelper mVerticalHelper; 44b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 45b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Nullable 46b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private OrientationHelper mHorizontalHelper; 47b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 48b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Override 49b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager, 50b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @NonNull View targetView) { 51b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int[] out = new int[2]; 52b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 53b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen out[0] = layoutManager.canScrollHorizontally() 54b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen ? getHorizontalHelper(layoutManager).getDecoratedStart(targetView) 55b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen : 0; 56b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 57b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen out[1] = layoutManager.canScrollVertically() 58b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen ? getVerticalHelper(layoutManager).getDecoratedStart(targetView) 59b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen : 0; 60b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 61b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return out; 62b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 63b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 64b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** 65b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Finds the view to snap to. The view to snap to is the child of the LayoutManager that is 66b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * closest to the start of the RecyclerView. The "start" depends on if the LayoutManager 67b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * is scrolling horizontally or vertically. If it is horizontally scrolling, then the 68b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * start is the view on the left (right if RTL). Otherwise, it is the top-most view. 69b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 70b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param layoutManager The current {@link RecyclerView.LayoutManager} for the attached 71b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * RecyclerView. 72b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @return The View closest to the start of the RecyclerView. 73b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 74b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Override 75b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Nullable 76b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen public View findSnapView(RecyclerView.LayoutManager layoutManager) { 77b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int childCount = layoutManager.getChildCount(); 78b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (childCount == 0) { 79b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return null; 80b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 81b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 82b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // If there's only one child, then that will be the snap target. 83b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (childCount == 1) { 84b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return layoutManager.getChildAt(0); 85b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 86b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 87b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen OrientationHelper orientationHelper = layoutManager.canScrollVertically() 88b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen ? getVerticalHelper(layoutManager) 89b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen : getHorizontalHelper(layoutManager); 90b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 91b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen View lastVisibleChild = layoutManager.getChildAt(childCount - 1); 92b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 93b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // Check if the last child visible is the last item in the list. 94b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen boolean lastItemVisible = 95b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen layoutManager.getPosition(lastVisibleChild) == layoutManager.getItemCount() - 1; 96b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 97b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // If it is, then check how much of that view is visible. 98b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen float lastItemPercentageVisible = lastItemVisible 99b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen ? getPercentageVisible(lastVisibleChild, orientationHelper) : 0; 100b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 101b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen View closestChild = null; 102b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int closestDistanceToStart = Integer.MAX_VALUE; 103b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen float closestPercentageVisible = 0.f; 104b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 105b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen for (int i = 0; i < childCount; i++) { 106b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen View child = layoutManager.getChildAt(i); 107b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int startOffset = orientationHelper.getDecoratedStart(child); 108b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 109b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (Math.abs(startOffset) < closestDistanceToStart) { 110b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen float percentageVisible = getPercentageVisible(child, orientationHelper); 111b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 112b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // Only snap to the child that is closest to the top and is more than 113b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // half-way visible. 114b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (percentageVisible > VIEW_VISIBLE_THRESHOLD 115b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen && percentageVisible > closestPercentageVisible) { 116b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen closestDistanceToStart = startOffset; 117b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen closestChild = child; 118b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen closestPercentageVisible = percentageVisible; 119b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 120b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 121b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 122b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 123b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // Snap to the last child in the list if it's the last item in the list, and it's more 124b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // visible than the closest item to the top of the list. 125b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return (lastItemVisible && lastItemPercentageVisible > closestPercentageVisible) 126b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen ? lastVisibleChild 127b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen : closestChild; 128b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 129b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 130b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** 131b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Returns the percentage of the given view that is visible, relative to its containing 132b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * RecyclerView. 133b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 134b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param view The View to get the percentage visible of. 135b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param helper An {@link OrientationHelper} to aid with calculation. 136b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @return A float indicating the percentage of the given view that is visible. 137b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 138b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private float getPercentageVisible(View view, OrientationHelper helper) { 139b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int start = 0; 140b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int end = helper.getEnd(); 141b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 142b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int viewStart = helper.getDecoratedStart(view); 143b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int viewEnd = helper.getDecoratedEnd(view); 144b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 145b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (viewStart >= start && viewEnd <= end) { 146b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // The view is within the bounds of the RecyclerView, so it's fully visible. 147b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return 1.f; 148b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } else if (viewStart <= start && viewEnd >= end) { 149b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // The view is larger than the height of the RecyclerView. 150b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int viewHeight = helper.getDecoratedMeasurement(view); 151b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return 1.f - ((float) (Math.abs(viewStart) + Math.abs(viewEnd)) / viewHeight); 152b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } else if (viewStart < start) { 153b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // The view is above the start of the RecyclerView, so subtract the start offset 154b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // from the total height. 155b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return 1.f - ((float) Math.abs(viewStart) / helper.getDecoratedMeasurement(view)); 156b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } else { 157b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // The view is below the end of the RecyclerView, so subtract the end offset from the 158b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // total height. 159b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return 1.f - ((float) Math.abs(viewEnd) / helper.getDecoratedMeasurement(view)); 160b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 161b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 162b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 163b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Override 164b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen public void attachToRecyclerView(@Nullable RecyclerView recyclerView) { 165b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen super.attachToRecyclerView(recyclerView); 166b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen mRecyclerView = recyclerView; 167b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 168b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 169b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** 170b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Calculate the estimated scroll distance in each direction given velocities on both axes. 171b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * This method will clamp the maximum scroll distance so that a single fling will never scroll 172b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * more than one page. 173b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 174b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param velocityX Fling velocity on the horizontal axis. 175b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param velocityY Fling velocity on the vertical axis. 176b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @return An array holding the calculated distances in x and y directions respectively. 177b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 178b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @Override 179b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen public int[] calculateScrollDistance(int velocityX, int velocityY) { 180b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int[] outDist = super.calculateScrollDistance(velocityX, velocityY); 181b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 182b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (mRecyclerView == null) { 183b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return outDist; 184b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 185b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 186b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen RecyclerView.LayoutManager layoutManager = mRecyclerView.getLayoutManager(); 187b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (layoutManager == null || layoutManager.getChildCount() == 0) { 188b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return outDist; 189b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 190b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 191b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int lastChildPosition = isAtEnd(layoutManager) ? 0 : layoutManager.getChildCount() - 1; 192b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 193b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // The max and min distance is the total height of the RecyclerView minus the height of 194b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // the last child. This ensures that each scroll will never scroll more than a single 195b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // page on the RecyclerView. That is, the max scroll will make the last child the 196b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // first child and vice versa when scrolling the opposite way. 197b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int maxDistance = layoutManager.getHeight() - layoutManager.getDecoratedMeasuredHeight( 198b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen layoutManager.getChildAt(lastChildPosition)); 199b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int minDistance = -maxDistance; 200b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 201b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen outDist[0] = clamp(outDist[0], minDistance, maxDistance); 202b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen outDist[1] = clamp(outDist[1], minDistance, maxDistance); 203b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 204b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return outDist; 205b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 206b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 207b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** Returns {@code true} if the RecyclerView is completely displaying the first item. */ 208b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen public boolean isAtStart(RecyclerView.LayoutManager layoutManager) { 209b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (layoutManager == null || layoutManager.getChildCount() == 0) { 210b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return true; 211b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 212b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 213b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen View firstChild = layoutManager.getChildAt(0); 214b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen OrientationHelper orientationHelper = layoutManager.canScrollVertically() 215b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen ? getVerticalHelper(layoutManager) 216b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen : getHorizontalHelper(layoutManager); 217b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 218b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // Check that the first child is completely visible and is the first item in the list. 219b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return orientationHelper.getDecoratedStart(firstChild) >= 0 220b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen && layoutManager.getPosition(firstChild) == 0; 221b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 222b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 223b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** Returns {@code true} if the RecyclerView is completely displaying the last item. */ 224b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen public boolean isAtEnd(RecyclerView.LayoutManager layoutManager) { 225b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (layoutManager == null || layoutManager.getChildCount() == 0) { 226b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return true; 227b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 228b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 229b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen int childCount = layoutManager.getChildCount(); 230b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen View lastVisibleChild = layoutManager.getChildAt(childCount - 1); 231b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 232b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // The list has reached the bottom if the last child that is visible is the last item 233b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen // in the list and it's fully shown. 234b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return layoutManager.getPosition(lastVisibleChild) == (layoutManager.getItemCount() - 1) 235b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen && layoutManager.getDecoratedBottom(lastVisibleChild) <= layoutManager.getHeight(); 236b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 237b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 238b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @NonNull 239b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private OrientationHelper getVerticalHelper(@NonNull RecyclerView.LayoutManager layoutManager) { 240b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (mVerticalHelper == null || mVerticalHelper.getLayoutManager() != layoutManager) { 241b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen mVerticalHelper = OrientationHelper.createVerticalHelper(layoutManager); 242b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 243b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return mVerticalHelper; 244b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 245b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 246b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @NonNull 247b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private OrientationHelper getHorizontalHelper( 248b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen @NonNull RecyclerView.LayoutManager layoutManager) { 249b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen if (mHorizontalHelper == null || mHorizontalHelper.getLayoutManager() != layoutManager) { 250b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen mHorizontalHelper = OrientationHelper.createHorizontalHelper(layoutManager); 251b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 252b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return mHorizontalHelper; 253b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 254b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen 255b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen /** 256b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * Ensures that the given value falls between the range given by the min and max values. This 257b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * method does not check that the min value is greater than or equal to the max value. If the 258b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * parameters are not well-formed, this method's behavior is undefined. 259b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * 260b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param value The value to clamp. 261b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param min The minimum value the given value can be. 262b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @param max The maximum value the given value can be. 263b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * @return A number that falls between {@code min} or {@code max} or one of those values if the 264b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen * given value is less than or greater than {@code min} and {@code max} respectively. 265b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen */ 266b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen private static int clamp(int value, int min, int max) { 267b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen return Math.max(min, Math.min(max, value)); 268b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen } 269b226d4dcc396fe8837876dfa113143702dd23c26Anthony Chen} 270