/
ReactHorizontalScrollView.java
1246 lines (1070 loc) · 41.5 KB
/
ReactHorizontalScrollView.java
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/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
package com.facebook.react.views.scroll;
import android.animation.Animator;
import android.animation.ObjectAnimator;
import android.animation.PropertyValuesHolder;
import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Rect;
import android.graphics.drawable.ColorDrawable;
import android.graphics.drawable.Drawable;
import android.view.FocusFinder;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.accessibility.AccessibilityEvent;
import android.widget.HorizontalScrollView;
import android.widget.OverScroller;
import androidx.annotation.Nullable;
import androidx.core.view.AccessibilityDelegateCompat;
import androidx.core.view.ViewCompat;
import androidx.core.view.accessibility.AccessibilityNodeInfoCompat;
import com.facebook.common.logging.FLog;
import com.facebook.infer.annotation.Assertions;
import com.facebook.react.bridge.WritableMap;
import com.facebook.react.bridge.WritableNativeMap;
import com.facebook.react.common.ReactConstants;
import com.facebook.react.common.build.ReactBuildConfig;
import com.facebook.react.modules.i18nmanager.I18nUtil;
import com.facebook.react.uimanager.FabricViewStateManager;
import com.facebook.react.uimanager.MeasureSpecAssertions;
import com.facebook.react.uimanager.PixelUtil;
import com.facebook.react.uimanager.ReactClippingViewGroup;
import com.facebook.react.uimanager.ReactClippingViewGroupHelper;
import com.facebook.react.uimanager.ReactOverflowView;
import com.facebook.react.uimanager.ViewProps;
import com.facebook.react.uimanager.events.NativeGestureUtil;
import com.facebook.react.views.view.ReactViewBackgroundManager;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
/** Similar to {@link ReactScrollView} but only supports horizontal scrolling. */
public class ReactHorizontalScrollView extends HorizontalScrollView
implements ReactClippingViewGroup,
FabricViewStateManager.HasFabricViewStateManager,
ReactOverflowView {
private static boolean DEBUG_MODE = false && ReactBuildConfig.DEBUG;
private static String TAG = ReactHorizontalScrollView.class.getSimpleName();
private static int NO_SCROLL_POSITION = Integer.MIN_VALUE;
private static @Nullable Field sScrollerField;
private static boolean sTriedToGetScrollerField = false;
private static final String CONTENT_OFFSET_LEFT = "contentOffsetLeft";
private static final String CONTENT_OFFSET_TOP = "contentOffsetTop";
private static final String SCROLL_AWAY_PADDING_TOP = "scrollAwayPaddingTop";
private int mLayoutDirection;
private int mScrollXAfterMeasure = NO_SCROLL_POSITION;
private static final int UNSET_CONTENT_OFFSET = -1;
private final OnScrollDispatchHelper mOnScrollDispatchHelper = new OnScrollDispatchHelper();
private final @Nullable OverScroller mScroller;
private final VelocityHelper mVelocityHelper = new VelocityHelper();
private final Rect mRect = new Rect();
private boolean mActivelyScrolling;
private @Nullable Rect mClippingRect;
private @Nullable String mOverflow = ViewProps.HIDDEN;
private boolean mDragging;
private boolean mPagingEnabled = false;
private @Nullable Runnable mPostTouchRunnable;
private boolean mRemoveClippedSubviews;
private boolean mScrollEnabled = true;
private boolean mSendMomentumEvents;
private @Nullable FpsListener mFpsListener = null;
private @Nullable String mScrollPerfTag;
private @Nullable Drawable mEndBackground;
private int mEndFillColor = Color.TRANSPARENT;
private boolean mDisableIntervalMomentum = false;
private int mSnapInterval = 0;
private float mDecelerationRate = 0.985f;
private @Nullable List<Integer> mSnapOffsets;
private boolean mSnapToStart = true;
private boolean mSnapToEnd = true;
private ReactViewBackgroundManager mReactBackgroundManager;
private boolean mPagedArrowScrolling = false;
private int pendingContentOffsetX = UNSET_CONTENT_OFFSET;
private int pendingContentOffsetY = UNSET_CONTENT_OFFSET;
private final FabricViewStateManager mFabricViewStateManager = new FabricViewStateManager();
private @Nullable ValueAnimator mScrollAnimator;
private int mFinalAnimatedPositionScrollX = 0;
private int mFinalAnimatedPositionScrollY = 0;
private int mLastStateUpdateScrollX = -1;
private int mLastStateUpdateScrollY = -1;
private final Rect mTempRect = new Rect();
public ReactHorizontalScrollView(Context context) {
this(context, null);
}
public ReactHorizontalScrollView(Context context, @Nullable FpsListener fpsListener) {
super(context);
mReactBackgroundManager = new ReactViewBackgroundManager(this);
mFpsListener = fpsListener;
ViewCompat.setAccessibilityDelegate(
this,
new AccessibilityDelegateCompat() {
@Override
public void onInitializeAccessibilityEvent(View host, AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(host, event);
event.setScrollable(mScrollEnabled);
}
@Override
public void onInitializeAccessibilityNodeInfo(
View host, AccessibilityNodeInfoCompat info) {
super.onInitializeAccessibilityNodeInfo(host, info);
info.setScrollable(mScrollEnabled);
}
});
mScroller = getOverScrollerFromParent();
mLayoutDirection =
I18nUtil.getInstance().isRTL(context)
? ViewCompat.LAYOUT_DIRECTION_RTL
: ViewCompat.LAYOUT_DIRECTION_LTR;
}
@Nullable
private OverScroller getOverScrollerFromParent() {
OverScroller scroller;
if (!sTriedToGetScrollerField) {
sTriedToGetScrollerField = true;
try {
sScrollerField = HorizontalScrollView.class.getDeclaredField("mScroller");
sScrollerField.setAccessible(true);
} catch (NoSuchFieldException e) {
FLog.w(
TAG,
"Failed to get mScroller field for HorizontalScrollView! "
+ "This app will exhibit the bounce-back scrolling bug :(");
}
}
if (sScrollerField != null) {
try {
Object scrollerValue = sScrollerField.get(this);
if (scrollerValue instanceof OverScroller) {
scroller = (OverScroller) scrollerValue;
} else {
FLog.w(
TAG,
"Failed to cast mScroller field in HorizontalScrollView (probably due to OEM changes to AOSP)! "
+ "This app will exhibit the bounce-back scrolling bug :(");
scroller = null;
}
} catch (IllegalAccessException e) {
throw new RuntimeException("Failed to get mScroller from HorizontalScrollView!", e);
}
} else {
scroller = null;
}
return scroller;
}
public void setScrollPerfTag(@Nullable String scrollPerfTag) {
mScrollPerfTag = scrollPerfTag;
}
@Override
public void setRemoveClippedSubviews(boolean removeClippedSubviews) {
if (removeClippedSubviews && mClippingRect == null) {
mClippingRect = new Rect();
}
mRemoveClippedSubviews = removeClippedSubviews;
updateClippingRect();
}
@Override
public boolean getRemoveClippedSubviews() {
return mRemoveClippedSubviews;
}
public void setDisableIntervalMomentum(boolean disableIntervalMomentum) {
mDisableIntervalMomentum = disableIntervalMomentum;
}
public void setSendMomentumEvents(boolean sendMomentumEvents) {
mSendMomentumEvents = sendMomentumEvents;
}
public void setScrollEnabled(boolean scrollEnabled) {
mScrollEnabled = scrollEnabled;
}
public void setPagingEnabled(boolean pagingEnabled) {
mPagingEnabled = pagingEnabled;
}
public void setDecelerationRate(float decelerationRate) {
mDecelerationRate = decelerationRate;
if (mScroller != null) {
mScroller.setFriction(1.0f - mDecelerationRate);
}
}
public void setSnapInterval(int snapInterval) {
mSnapInterval = snapInterval;
}
public void setSnapOffsets(List<Integer> snapOffsets) {
mSnapOffsets = snapOffsets;
}
public void setSnapToStart(boolean snapToStart) {
mSnapToStart = snapToStart;
}
public void setSnapToEnd(boolean snapToEnd) {
mSnapToEnd = snapToEnd;
}
public void flashScrollIndicators() {
awakenScrollBars();
}
public void setOverflow(String overflow) {
mOverflow = overflow;
invalidate();
}
@Override
public @Nullable String getOverflow() {
return mOverflow;
}
@Override
protected void onDraw(Canvas canvas) {
if (DEBUG_MODE) {
FLog.i(TAG, "onDraw[%d]", getId());
}
getDrawingRect(mRect);
switch (mOverflow) {
case ViewProps.VISIBLE:
break;
default:
canvas.clipRect(mRect);
break;
}
super.onDraw(canvas);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
MeasureSpecAssertions.assertExplicitMeasureSpec(widthMeasureSpec, heightMeasureSpec);
int measuredWidth = MeasureSpec.getSize(widthMeasureSpec);
int measuredHeight = MeasureSpec.getSize(heightMeasureSpec);
if (DEBUG_MODE) {
FLog.i(
TAG,
"onMeasure[%d] measured width: %d measured height: %d",
getId(),
measuredWidth,
measuredHeight);
}
boolean measuredHeightChanged = getMeasuredHeight() != measuredHeight;
setMeasuredDimension(measuredWidth, measuredHeight);
// See how `mScrollXAfterMeasure` is used in `onLayout`, and why we only enable the
// hack if the height has changed.
if (measuredHeightChanged && mScroller != null) {
mScrollXAfterMeasure = mScroller.getCurrX();
}
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (DEBUG_MODE) {
FLog.i(TAG, "onLayout[%d] l %d t %d r %d b %d", getId(), l, t, r, b);
}
// Has the scrollX changed between the last onMeasure and this layout?
// If so, cancel the animation.
// Essentially, if the height changes (due to keyboard popping up, for instance) the
// underlying View.layout method will in some cases scroll to an incorrect X position -
// see also the hacks in `fling`. The order of layout is called in the order of: onMeasure,
// layout, onLayout.
// We cannot override `layout` but we can detect the sequence of events between onMeasure
// and onLayout.
if (mScrollXAfterMeasure != NO_SCROLL_POSITION
&& mScroller != null
&& mScrollXAfterMeasure != mScroller.getFinalX()
&& !mScroller.isFinished()) {
if (DEBUG_MODE) {
FLog.i(
TAG,
"onLayout[%d] scroll hack enabled: reset to previous scrollX position of %d",
getId(),
mScrollXAfterMeasure);
}
mScroller.startScroll(mScrollXAfterMeasure, mScroller.getFinalY(), 0, 0);
mScroller.forceFinished(true);
mScrollXAfterMeasure = NO_SCROLL_POSITION;
}
// Call with the present values in order to re-layout if necessary
// If a "pending" value has been set, we restore that value.
// That value gets cleared by reactScrollTo.
int scrollToX =
pendingContentOffsetX != UNSET_CONTENT_OFFSET ? pendingContentOffsetX : getScrollX();
int scrollToY =
pendingContentOffsetY != UNSET_CONTENT_OFFSET ? pendingContentOffsetY : getScrollY();
scrollTo(scrollToX, scrollToY);
ReactScrollViewHelper.emitLayoutEvent(this);
}
/**
* Since ReactHorizontalScrollView handles layout changes on JS side, it does not call
* super.onlayout due to which mIsLayoutDirty flag in HorizontalScrollView remains true and
* prevents scrolling to child when requestChildFocus is called. Overriding this method and
* scrolling to child without checking any layout dirty flag. This will fix focus navigation issue
* for KeyEvents which are not handled in HorizontalScrollView, for example: KEYCODE_TAB.
*/
@Override
public void requestChildFocus(View child, View focused) {
if (focused != null && !mPagingEnabled) {
scrollToChild(focused);
}
super.requestChildFocus(child, focused);
}
@Override
public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {
if (mPagingEnabled && !mPagedArrowScrolling) {
// Only add elements within the current page to list of focusables
ArrayList<View> candidateViews = new ArrayList<View>();
super.addFocusables(candidateViews, direction, focusableMode);
for (View candidate : candidateViews) {
// We must also include the currently focused in the focusables list or focus search will
// always
// return the first element within the focusables list
if (isScrolledInView(candidate)
|| isPartiallyScrolledInView(candidate)
|| candidate.isFocused()) {
views.add(candidate);
}
}
} else {
super.addFocusables(views, direction, focusableMode);
}
}
/** Calculates the x delta required to scroll the given descendent into view */
private int getScrollDelta(View descendent) {
descendent.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(descendent, mTempRect);
return computeScrollDeltaToGetChildRectOnScreen(mTempRect);
}
/** Returns whether the given descendent is scrolled fully in view */
private boolean isScrolledInView(View descendent) {
return getScrollDelta(descendent) == 0;
}
/** Returns whether the given descendent is partially scrolled in view */
private boolean isPartiallyScrolledInView(View descendent) {
int scrollDelta = getScrollDelta(descendent);
descendent.getDrawingRect(mTempRect);
return scrollDelta != 0 && Math.abs(scrollDelta) < mTempRect.width();
}
/** Returns whether the given descendent is "mostly" (>50%) scrolled in view */
private boolean isMostlyScrolledInView(View descendent) {
int scrollDelta = getScrollDelta(descendent);
descendent.getDrawingRect(mTempRect);
return scrollDelta != 0 && Math.abs(scrollDelta) < (mTempRect.width() / 2);
}
private void scrollToChild(View child) {
int scrollDelta = getScrollDelta(child);
if (scrollDelta != 0) {
scrollBy(scrollDelta, 0);
}
}
@Override
protected void onScrollChanged(int x, int y, int oldX, int oldY) {
if (DEBUG_MODE) {
FLog.i(TAG, "onScrollChanged[%d] x %d y %d oldx %d oldy %d", getId(), x, y, oldX, oldY);
}
super.onScrollChanged(x, y, oldX, oldY);
mActivelyScrolling = true;
if (mOnScrollDispatchHelper.onScrollChanged(x, y)) {
if (mRemoveClippedSubviews) {
updateClippingRect();
}
// Race an UpdateState with every onScroll. This makes it more likely that, in Fabric,
// when JS processes the scroll event, the C++ ShadowNode representation will have a
// "more correct" scroll position. It will frequently be /incorrect/ but this decreases
// the error as much as possible.
updateStateOnScroll();
ReactScrollViewHelper.emitScrollEvent(
this,
mOnScrollDispatchHelper.getXFlingVelocity(),
mOnScrollDispatchHelper.getYFlingVelocity());
}
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (!mScrollEnabled) {
return false;
}
try {
if (super.onInterceptTouchEvent(ev)) {
NativeGestureUtil.notifyNativeGestureStarted(this, ev);
ReactScrollViewHelper.emitScrollBeginDragEvent(this);
mDragging = true;
enableFpsListener();
return true;
}
} catch (IllegalArgumentException e) {
// Log and ignore the error. This seems to be a bug in the android SDK and
// this is the commonly accepted workaround.
// https://tinyurl.com/mw6qkod (Stack Overflow)
FLog.w(ReactConstants.TAG, "Error intercepting touch event.", e);
}
return false;
}
@Override
public boolean pageScroll(int direction) {
boolean handled = super.pageScroll(direction);
if (mPagingEnabled && handled) {
handlePostTouchScrolling(0, 0);
}
return handled;
}
@Override
public boolean arrowScroll(int direction) {
boolean handled = false;
if (mPagingEnabled) {
mPagedArrowScrolling = true;
if (getChildCount() > 0) {
View currentFocused = findFocus();
View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);
View rootChild = getContentView();
if (rootChild != null && nextFocused != null && nextFocused.getParent() == rootChild) {
if (!isScrolledInView(nextFocused) && !isMostlyScrolledInView(nextFocused)) {
smoothScrollToNextPage(direction);
}
nextFocused.requestFocus();
handled = true;
} else {
smoothScrollToNextPage(direction);
handled = true;
}
}
mPagedArrowScrolling = false;
} else {
handled = super.arrowScroll(direction);
}
return handled;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (!mScrollEnabled) {
return false;
}
mVelocityHelper.calculateVelocity(ev);
int action = ev.getAction() & MotionEvent.ACTION_MASK;
if (action == MotionEvent.ACTION_UP && mDragging) {
updateStateOnScroll();
float velocityX = mVelocityHelper.getXVelocity();
float velocityY = mVelocityHelper.getYVelocity();
ReactScrollViewHelper.emitScrollEndDragEvent(this, velocityX, velocityY);
mDragging = false;
// After the touch finishes, we may need to do some scrolling afterwards either as a result
// of a fling or because we need to page align the content
handlePostTouchScrolling(Math.round(velocityX), Math.round(velocityY));
}
return super.onTouchEvent(ev);
}
@Override
public boolean executeKeyEvent(KeyEvent event) {
int eventKeyCode = event.getKeyCode();
if (!mScrollEnabled
&& (eventKeyCode == KeyEvent.KEYCODE_DPAD_LEFT
|| eventKeyCode == KeyEvent.KEYCODE_DPAD_RIGHT)) {
return false;
}
return super.executeKeyEvent(event);
}
@Override
public void fling(int velocityX) {
if (DEBUG_MODE) {
FLog.i(TAG, "fling[%d] velocityX %d", getId(), velocityX);
}
// Workaround.
// On Android P if a ScrollView is inverted, we will get a wrong sign for
// velocityX (see https://issuetracker.google.com/issues/112385925).
// At the same time, mOnScrollDispatchHelper tracks the correct velocity direction.
//
// Hence, we can use the absolute value from whatever the OS gives
// us and use the sign of what mOnScrollDispatchHelper has tracked.
final int correctedVelocityX =
(int) (Math.abs(velocityX) * Math.signum(mOnScrollDispatchHelper.getXFlingVelocity()));
if (mPagingEnabled) {
flingAndSnap(correctedVelocityX);
} else if (mScroller != null) {
// FB SCROLLVIEW CHANGE
// We provide our own version of fling that uses a different call to the standard OverScroller
// which takes into account the possibility of adding new content while the ScrollView is
// animating. Because we give essentially no max X for the fling, the fling will continue as
// long
// as there is content. See #onOverScrolled() to see the second part of this change which
// properly
// aborts the scroller animation when we get to the bottom of the ScrollView content.
int scrollWindowWidth =
getWidth() - ViewCompat.getPaddingStart(this) - ViewCompat.getPaddingEnd(this);
mScroller.fling(
getScrollX(), // startX
getScrollY(), // startY
correctedVelocityX, // velocityX
0, // velocityY
0, // minX
Integer.MAX_VALUE, // maxX
0, // minY
0, // maxY
scrollWindowWidth / 2, // overX
0 // overY
);
ViewCompat.postInvalidateOnAnimation(this);
// END FB SCROLLVIEW CHANGE
} else {
super.fling(correctedVelocityX);
}
handlePostTouchScrolling(correctedVelocityX, 0);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
if (mRemoveClippedSubviews) {
updateClippingRect();
}
}
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
if (mRemoveClippedSubviews) {
updateClippingRect();
}
}
@Override
public void updateClippingRect() {
if (!mRemoveClippedSubviews) {
return;
}
Assertions.assertNotNull(mClippingRect);
ReactClippingViewGroupHelper.calculateClippingRect(this, mClippingRect);
View contentView = getContentView();
if (contentView instanceof ReactClippingViewGroup) {
((ReactClippingViewGroup) contentView).updateClippingRect();
}
}
@Override
public void getClippingRect(Rect outClippingRect) {
outClippingRect.set(Assertions.assertNotNull(mClippingRect));
}
@Override
public boolean getChildVisibleRect(View child, Rect r, android.graphics.Point offset) {
return super.getChildVisibleRect(child, r, offset);
}
private int getSnapInterval() {
if (mSnapInterval != 0) {
return mSnapInterval;
}
return getWidth();
}
private View getContentView() {
View contentView = getChildAt(0);
return contentView;
}
public void setEndFillColor(int color) {
if (color != mEndFillColor) {
mEndFillColor = color;
mEndBackground = new ColorDrawable(mEndFillColor);
}
}
@Override
protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX, boolean clampedY) {
if (DEBUG_MODE) {
FLog.i(
TAG,
"onOverScrolled[%d] scrollX %d scrollY %d clampedX %b clampedY %b",
getId(),
scrollX,
scrollY,
clampedX,
clampedY);
}
if (mScroller != null) {
// FB SCROLLVIEW CHANGE
// This is part two of the reimplementation of fling to fix the bounce-back bug. See #fling()
// for
// more information.
if (!mScroller.isFinished() && mScroller.getCurrX() != mScroller.getFinalX()) {
int scrollRange = computeHorizontalScrollRange() - getWidth();
if (scrollX >= scrollRange) {
mScroller.abortAnimation();
scrollX = scrollRange;
}
}
// END FB SCROLLVIEW CHANGE
}
super.onOverScrolled(scrollX, scrollY, clampedX, clampedY);
}
private void enableFpsListener() {
if (isScrollPerfLoggingEnabled()) {
Assertions.assertNotNull(mFpsListener);
Assertions.assertNotNull(mScrollPerfTag);
mFpsListener.enable(mScrollPerfTag);
}
}
private void disableFpsListener() {
if (isScrollPerfLoggingEnabled()) {
Assertions.assertNotNull(mFpsListener);
Assertions.assertNotNull(mScrollPerfTag);
mFpsListener.disable(mScrollPerfTag);
}
}
private boolean isScrollPerfLoggingEnabled() {
return mFpsListener != null && mScrollPerfTag != null && !mScrollPerfTag.isEmpty();
}
@Override
public void draw(Canvas canvas) {
if (mEndFillColor != Color.TRANSPARENT) {
final View content = getContentView();
if (mEndBackground != null && content != null && content.getRight() < getWidth()) {
mEndBackground.setBounds(content.getRight(), 0, getWidth(), getHeight());
mEndBackground.draw(canvas);
}
}
super.draw(canvas);
}
/**
* This handles any sort of scrolling that may occur after a touch is finished. This may be
* momentum scrolling (fling) or because you have pagingEnabled on the scroll view. Because we
* don't get any events from Android about this lifecycle, we do all our detection by creating a
* runnable that checks if we scrolled in the last frame and if so assumes we are still scrolling.
*/
private void handlePostTouchScrolling(int velocityX, int velocityY) {
if (DEBUG_MODE) {
FLog.i(
TAG,
"handlePostTouchScrolling[%d] velocityX %d velocityY %d",
getId(),
velocityX,
velocityY);
}
// Check if we are already handling this which may occur if this is called by both the touch up
// and a fling call
if (mPostTouchRunnable != null) {
return;
}
if (mSendMomentumEvents) {
ReactScrollViewHelper.emitScrollMomentumBeginEvent(this, velocityX, velocityY);
}
mActivelyScrolling = false;
mPostTouchRunnable =
new Runnable() {
private boolean mSnappingToPage = false;
private boolean mRunning = true;
private int mStableFrames = 0;
@Override
public void run() {
if (mActivelyScrolling) {
// We are still scrolling.
mActivelyScrolling = false;
mStableFrames = 0;
mRunning = true;
} else {
// There has not been a scroll update since the last time this Runnable executed.
updateStateOnScroll();
// We keep checking for updates until the ScrollView has "stabilized" and hasn't
// scrolled for N consecutive frames. This number is arbitrary: big enough to catch
// a number of race conditions, but small enough to not cause perf regressions, etc.
// In anecdotal testing, it seemed like a decent number.
// Without this check, sometimes this Runnable stops executing too soon - it will
// fire before the first scroll event of an animated scroll/fling, and stop
// immediately.
mStableFrames++;
mRunning = (mStableFrames < 3);
if (mPagingEnabled && !mSnappingToPage) {
// Only if we have pagingEnabled and we have not snapped to the page do we
// need to continue checking for the scroll. And we cause that scroll by asking for
// it
mSnappingToPage = true;
flingAndSnap(0);
ViewCompat.postOnAnimationDelayed(
ReactHorizontalScrollView.this, this, ReactScrollViewHelper.MOMENTUM_DELAY);
} else {
if (mSendMomentumEvents) {
ReactScrollViewHelper.emitScrollMomentumEndEvent(ReactHorizontalScrollView.this);
}
disableFpsListener();
}
}
// We are still scrolling so we just post to check again a frame later
if (mRunning) {
ViewCompat.postOnAnimationDelayed(
ReactHorizontalScrollView.this, this, ReactScrollViewHelper.MOMENTUM_DELAY);
} else {
mPostTouchRunnable = null;
}
}
};
ViewCompat.postOnAnimationDelayed(
this, mPostTouchRunnable, ReactScrollViewHelper.MOMENTUM_DELAY);
}
/** Get current X position or position after current animation finishes, if any. */
private int getPostAnimationScrollX() {
return mScrollAnimator != null && mScrollAnimator.isRunning()
? mFinalAnimatedPositionScrollX
: getScrollX();
}
/** Get current X position or position after current animation finishes, if any. */
private int getPostAnimationScrollY() {
return mScrollAnimator != null && mScrollAnimator.isRunning()
? mFinalAnimatedPositionScrollY
: getScrollY();
}
private int predictFinalScrollPosition(int velocityX) {
// ScrollView can *only* scroll for 250ms when using smoothScrollTo and there's
// no way to customize the scroll duration. So, we create a temporary OverScroller
// so we can predict where a fling would land and snap to nearby that point.
OverScroller scroller = new OverScroller(getContext());
scroller.setFriction(1.0f - mDecelerationRate);
// predict where a fling would end up so we can scroll to the nearest snap offset
int maximumOffset = Math.max(0, computeHorizontalScrollRange() - getWidth());
int width = getWidth() - ViewCompat.getPaddingStart(this) - ViewCompat.getPaddingEnd(this);
scroller.fling(
getPostAnimationScrollX(), // startX
getPostAnimationScrollY(), // startY
velocityX, // velocityX
0, // velocityY
0, // minX
maximumOffset, // maxX
0, // minY
0, // maxY
width / 2, // overX
0 // overY
);
return scroller.getFinalX();
}
/**
* This will smooth scroll us to the nearest snap offset point. It currently just looks at where
* the content is and slides to the nearest point. It is intended to be run after we are done
* scrolling, and handling any momentum scrolling.
*/
private void smoothScrollAndSnap(int velocity) {
if (DEBUG_MODE) {
FLog.i(TAG, "smoothScrollAndSnap[%d] velocity %d", getId(), velocity);
}
double interval = (double) getSnapInterval();
double currentOffset = (double) (getPostAnimationScrollX());
double targetOffset = (double) predictFinalScrollPosition(velocity);
int previousPage = (int) Math.floor(currentOffset / interval);
int nextPage = (int) Math.ceil(currentOffset / interval);
int currentPage = (int) Math.round(currentOffset / interval);
int targetPage = (int) Math.round(targetOffset / interval);
if (velocity > 0 && nextPage == previousPage) {
nextPage++;
} else if (velocity < 0 && previousPage == nextPage) {
previousPage--;
}
if (
// if scrolling towards next page
velocity > 0
&&
// and the middle of the page hasn't been crossed already
currentPage < nextPage
&&
// and it would have been crossed after flinging
targetPage > previousPage) {
currentPage = nextPage;
} else if (
// if scrolling towards previous page
velocity < 0
&&
// and the middle of the page hasn't been crossed already
currentPage > previousPage
&&
// and it would have been crossed after flinging
targetPage < nextPage) {
currentPage = previousPage;
}
targetOffset = currentPage * interval;
if (targetOffset != currentOffset) {
mActivelyScrolling = true;
reactSmoothScrollTo((int) targetOffset, getScrollY());
}
}
private void flingAndSnap(int velocityX) {
if (DEBUG_MODE) {
FLog.i(TAG, "smoothScrollAndSnap[%d] velocityX %d", getId(), velocityX);
}
if (getChildCount() <= 0) {
return;
}
// pagingEnabled only allows snapping one interval at a time
if (mSnapInterval == 0 && mSnapOffsets == null) {
smoothScrollAndSnap(velocityX);
return;
}
int maximumOffset = Math.max(0, computeHorizontalScrollRange() - getWidth());
int targetOffset = predictFinalScrollPosition(velocityX);
if (mDisableIntervalMomentum) {
targetOffset = getScrollX();
}
int smallerOffset = 0;
int largerOffset = maximumOffset;
int firstOffset = 0;
int lastOffset = maximumOffset;
int width = getWidth() - ViewCompat.getPaddingStart(this) - ViewCompat.getPaddingEnd(this);
// offsets are from the right edge in RTL layouts
if (mLayoutDirection == LAYOUT_DIRECTION_RTL) {
targetOffset = maximumOffset - targetOffset;
velocityX = -velocityX;
}
// get the nearest snap points to the target offset
if (mSnapOffsets != null && !mSnapOffsets.isEmpty()) {
firstOffset = mSnapOffsets.get(0);
lastOffset = mSnapOffsets.get(mSnapOffsets.size() - 1);
for (int i = 0; i < mSnapOffsets.size(); i++) {
int offset = mSnapOffsets.get(i);
if (offset <= targetOffset) {
if (targetOffset - offset < targetOffset - smallerOffset) {
smallerOffset = offset;
}
}
if (offset >= targetOffset) {
if (offset - targetOffset < largerOffset - targetOffset) {
largerOffset = offset;
}
}
}
} else {
double interval = (double) getSnapInterval();
double ratio = (double) targetOffset / interval;
smallerOffset = (int) (Math.floor(ratio) * interval);
largerOffset = Math.min((int) (Math.ceil(ratio) * interval), maximumOffset);
}
// Calculate the nearest offset
int nearestOffset =
targetOffset - smallerOffset < largerOffset - targetOffset ? smallerOffset : largerOffset;
// if scrolling after the last snap offset and snapping to the
// end of the list is disabled, then we allow free scrolling
int currentOffset = getScrollX();
if (mLayoutDirection == LAYOUT_DIRECTION_RTL) {
currentOffset = maximumOffset - currentOffset;
}
if (!mSnapToEnd && targetOffset >= lastOffset) {
if (currentOffset >= lastOffset) {
// free scrolling
} else {
// snap to end
targetOffset = lastOffset;
}
} else if (!mSnapToStart && targetOffset <= firstOffset) {
if (currentOffset <= firstOffset) {
// free scrolling
} else {
// snap to beginning
targetOffset = firstOffset;
}
} else if (velocityX > 0) {
// when snapping velocity can feel sluggish for slow swipes
velocityX += (int) ((largerOffset - targetOffset) * 10.0);
targetOffset = largerOffset;
} else if (velocityX < 0) {
// when snapping velocity can feel sluggish for slow swipes
velocityX -= (int) ((targetOffset - smallerOffset) * 10.0);
targetOffset = smallerOffset;
} else {
targetOffset = nearestOffset;
}
// Make sure the new offset isn't out of bounds
targetOffset = Math.min(Math.max(0, targetOffset), maximumOffset);
if (mLayoutDirection == LAYOUT_DIRECTION_RTL) {
targetOffset = maximumOffset - targetOffset;