Import Android SDK Platform P [4697573]
/google/data/ro/projects/android/fetch_artifact \
--bid 4697573 \
--target sdk_phone_armv7-win_sdk \
sdk-repo-linux-sources-4697573.zip
AndroidVersion.ApiLevel has been modified to appear as 28
Change-Id: If80578c3c657366cc9cf75f8db13d46e2dd4e077
diff --git a/androidx/recyclerview/widget/PagerSnapHelper.java b/androidx/recyclerview/widget/PagerSnapHelper.java
new file mode 100644
index 0000000..d162e52
--- /dev/null
+++ b/androidx/recyclerview/widget/PagerSnapHelper.java
@@ -0,0 +1,256 @@
+/*
+ * Copyright 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package androidx.recyclerview.widget;
+
+import android.graphics.PointF;
+import android.util.DisplayMetrics;
+import android.view.View;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.viewpager.widget.ViewPager;
+
+/**
+ * Implementation of the {@link SnapHelper} supporting pager style snapping in either vertical or
+ * horizontal orientation.
+ *
+ * <p>
+ *
+ * PagerSnapHelper can help achieve a similar behavior to {@link ViewPager}.
+ * Set both {@link RecyclerView} and the items of the
+ * {@link RecyclerView.Adapter} to have
+ * {@link android.view.ViewGroup.LayoutParams#MATCH_PARENT} height and width and then attach
+ * PagerSnapHelper to the {@link RecyclerView} using {@link #attachToRecyclerView(RecyclerView)}.
+ */
+public class PagerSnapHelper extends SnapHelper {
+ private static final int MAX_SCROLL_ON_FLING_DURATION = 100; // ms
+
+ // Orientation helpers are lazily created per LayoutManager.
+ @Nullable
+ private OrientationHelper mVerticalHelper;
+ @Nullable
+ private OrientationHelper mHorizontalHelper;
+
+ @Nullable
+ @Override
+ public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager,
+ @NonNull View targetView) {
+ int[] out = new int[2];
+ if (layoutManager.canScrollHorizontally()) {
+ out[0] = distanceToCenter(layoutManager, targetView,
+ getHorizontalHelper(layoutManager));
+ } else {
+ out[0] = 0;
+ }
+
+ if (layoutManager.canScrollVertically()) {
+ out[1] = distanceToCenter(layoutManager, targetView,
+ getVerticalHelper(layoutManager));
+ } else {
+ out[1] = 0;
+ }
+ return out;
+ }
+
+ @Nullable
+ @Override
+ public View findSnapView(RecyclerView.LayoutManager layoutManager) {
+ if (layoutManager.canScrollVertically()) {
+ return findCenterView(layoutManager, getVerticalHelper(layoutManager));
+ } else if (layoutManager.canScrollHorizontally()) {
+ return findCenterView(layoutManager, getHorizontalHelper(layoutManager));
+ }
+ return null;
+ }
+
+ @Override
+ public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager, int velocityX,
+ int velocityY) {
+ final int itemCount = layoutManager.getItemCount();
+ if (itemCount == 0) {
+ return RecyclerView.NO_POSITION;
+ }
+
+ View mStartMostChildView = null;
+ if (layoutManager.canScrollVertically()) {
+ mStartMostChildView = findStartView(layoutManager, getVerticalHelper(layoutManager));
+ } else if (layoutManager.canScrollHorizontally()) {
+ mStartMostChildView = findStartView(layoutManager, getHorizontalHelper(layoutManager));
+ }
+
+ if (mStartMostChildView == null) {
+ return RecyclerView.NO_POSITION;
+ }
+ final int centerPosition = layoutManager.getPosition(mStartMostChildView);
+ if (centerPosition == RecyclerView.NO_POSITION) {
+ return RecyclerView.NO_POSITION;
+ }
+
+ final boolean forwardDirection;
+ if (layoutManager.canScrollHorizontally()) {
+ forwardDirection = velocityX > 0;
+ } else {
+ forwardDirection = velocityY > 0;
+ }
+ boolean reverseLayout = false;
+ if ((layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
+ RecyclerView.SmoothScroller.ScrollVectorProvider vectorProvider =
+ (RecyclerView.SmoothScroller.ScrollVectorProvider) layoutManager;
+ PointF vectorForEnd = vectorProvider.computeScrollVectorForPosition(itemCount - 1);
+ if (vectorForEnd != null) {
+ reverseLayout = vectorForEnd.x < 0 || vectorForEnd.y < 0;
+ }
+ }
+ return reverseLayout
+ ? (forwardDirection ? centerPosition - 1 : centerPosition)
+ : (forwardDirection ? centerPosition + 1 : centerPosition);
+ }
+
+ @Override
+ protected LinearSmoothScroller createSnapScroller(RecyclerView.LayoutManager layoutManager) {
+ if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
+ return null;
+ }
+ return new LinearSmoothScroller(mRecyclerView.getContext()) {
+ @Override
+ protected void onTargetFound(View targetView, RecyclerView.State state, Action action) {
+ int[] snapDistances = calculateDistanceToFinalSnap(mRecyclerView.getLayoutManager(),
+ targetView);
+ final int dx = snapDistances[0];
+ final int dy = snapDistances[1];
+ final int time = calculateTimeForDeceleration(Math.max(Math.abs(dx), Math.abs(dy)));
+ if (time > 0) {
+ action.update(dx, dy, time, mDecelerateInterpolator);
+ }
+ }
+
+ @Override
+ protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
+ return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
+ }
+
+ @Override
+ protected int calculateTimeForScrolling(int dx) {
+ return Math.min(MAX_SCROLL_ON_FLING_DURATION, super.calculateTimeForScrolling(dx));
+ }
+ };
+ }
+
+ private int distanceToCenter(@NonNull RecyclerView.LayoutManager layoutManager,
+ @NonNull View targetView, OrientationHelper helper) {
+ final int childCenter = helper.getDecoratedStart(targetView)
+ + (helper.getDecoratedMeasurement(targetView) / 2);
+ final int containerCenter;
+ if (layoutManager.getClipToPadding()) {
+ containerCenter = helper.getStartAfterPadding() + helper.getTotalSpace() / 2;
+ } else {
+ containerCenter = helper.getEnd() / 2;
+ }
+ return childCenter - containerCenter;
+ }
+
+ /**
+ * Return the child view that is currently closest to the center of this parent.
+ *
+ * @param layoutManager The {@link RecyclerView.LayoutManager} associated with the attached
+ * {@link RecyclerView}.
+ * @param helper The relevant {@link OrientationHelper} for the attached {@link RecyclerView}.
+ *
+ * @return the child view that is currently closest to the center of this parent.
+ */
+ @Nullable
+ private View findCenterView(RecyclerView.LayoutManager layoutManager,
+ OrientationHelper helper) {
+ int childCount = layoutManager.getChildCount();
+ if (childCount == 0) {
+ return null;
+ }
+
+ View closestChild = null;
+ final int center;
+ if (layoutManager.getClipToPadding()) {
+ center = helper.getStartAfterPadding() + helper.getTotalSpace() / 2;
+ } else {
+ center = helper.getEnd() / 2;
+ }
+ int absClosest = Integer.MAX_VALUE;
+
+ for (int i = 0; i < childCount; i++) {
+ final View child = layoutManager.getChildAt(i);
+ int childCenter = helper.getDecoratedStart(child)
+ + (helper.getDecoratedMeasurement(child) / 2);
+ int absDistance = Math.abs(childCenter - center);
+
+ /** if child center is closer than previous closest, set it as closest **/
+ if (absDistance < absClosest) {
+ absClosest = absDistance;
+ closestChild = child;
+ }
+ }
+ return closestChild;
+ }
+
+ /**
+ * Return the child view that is currently closest to the start of this parent.
+ *
+ * @param layoutManager The {@link RecyclerView.LayoutManager} associated with the attached
+ * {@link RecyclerView}.
+ * @param helper The relevant {@link OrientationHelper} for the attached {@link RecyclerView}.
+ *
+ * @return the child view that is currently closest to the start of this parent.
+ */
+ @Nullable
+ private View findStartView(RecyclerView.LayoutManager layoutManager,
+ OrientationHelper helper) {
+ int childCount = layoutManager.getChildCount();
+ if (childCount == 0) {
+ return null;
+ }
+
+ View closestChild = null;
+ int startest = Integer.MAX_VALUE;
+
+ for (int i = 0; i < childCount; i++) {
+ final View child = layoutManager.getChildAt(i);
+ int childStart = helper.getDecoratedStart(child);
+
+ /** if child is more to start than previous closest, set it as closest **/
+ if (childStart < startest) {
+ startest = childStart;
+ closestChild = child;
+ }
+ }
+ return closestChild;
+ }
+
+ @NonNull
+ private OrientationHelper getVerticalHelper(@NonNull RecyclerView.LayoutManager layoutManager) {
+ if (mVerticalHelper == null || mVerticalHelper.mLayoutManager != layoutManager) {
+ mVerticalHelper = OrientationHelper.createVerticalHelper(layoutManager);
+ }
+ return mVerticalHelper;
+ }
+
+ @NonNull
+ private OrientationHelper getHorizontalHelper(
+ @NonNull RecyclerView.LayoutManager layoutManager) {
+ if (mHorizontalHelper == null || mHorizontalHelper.mLayoutManager != layoutManager) {
+ mHorizontalHelper = OrientationHelper.createHorizontalHelper(layoutManager);
+ }
+ return mHorizontalHelper;
+ }
+}
