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Add maintainVisibleContentPosition support on Android (#35049)
Summary: This adds support for `maintainVisibleContentPosition` on Android. The implementation is heavily inspired from iOS, it works by finding the first visible view and its frame before views are update, then adjusting the scroll position once the views are updated. Most of the logic is abstracted away in MaintainVisibleScrollPositionHelper to be used in both vertical and horizontal scrollview implementations. Note that this only works for the old architecture, I have a follow up ready to add fabric support. ## Changelog <!-- Help reviewers and the release process by writing your own changelog entry. For an example, see: https://reactnative.dev/contributing/changelogs-in-pull-requests --> [Android] [Added] - Add maintainVisibleContentPosition support on Android Pull Request resolved: #35049 Test Plan: Test in RN tester example on Android https://user-images.githubusercontent.com/2677334/197319855-d81ced33-a80b-495f-a688-4106fc699f3c.mov Reviewed By: ryancat Differential Revision: D40642469 Pulled By: skinsshark fbshipit-source-id: d60f3e2d0613d21af5f150ca0d099beeac6feb91
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...id/src/main/java/com/facebook/react/views/scroll/MaintainVisibleScrollPositionHelper.java
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| /* | ||
| * Copyright (c) Meta Platforms, Inc. and affiliates. | ||
| * | ||
| * This source code is licensed under the MIT license found in the | ||
| * LICENSE file in the root directory of this source tree. | ||
| */ | ||
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| package com.facebook.react.views.scroll; | ||
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| import android.graphics.Rect; | ||
| import android.view.View; | ||
| import android.view.ViewGroup; | ||
| import androidx.annotation.Nullable; | ||
| import com.facebook.infer.annotation.Assertions; | ||
| import com.facebook.react.bridge.ReactContext; | ||
| import com.facebook.react.bridge.ReadableMap; | ||
| import com.facebook.react.bridge.UIManager; | ||
| import com.facebook.react.bridge.UIManagerListener; | ||
| import com.facebook.react.bridge.UiThreadUtil; | ||
| import com.facebook.react.uimanager.UIManagerHelper; | ||
| import com.facebook.react.uimanager.common.ViewUtil; | ||
| import com.facebook.react.views.scroll.ReactScrollViewHelper.HasSmoothScroll; | ||
| import com.facebook.react.views.view.ReactViewGroup; | ||
| import java.lang.ref.WeakReference; | ||
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| /** | ||
| * Manage state for the maintainVisibleContentPosition prop. | ||
| * | ||
| * <p>This uses UIManager to listen to updates and capture position of items before and after | ||
| * layout. | ||
| */ | ||
| public class MaintainVisibleScrollPositionHelper<ScrollViewT extends ViewGroup & HasSmoothScroll> | ||
| implements UIManagerListener { | ||
| private final ScrollViewT mScrollView; | ||
| private final boolean mHorizontal; | ||
| private @Nullable Config mConfig; | ||
| private @Nullable WeakReference<View> mFirstVisibleView = null; | ||
| private @Nullable Rect mPrevFirstVisibleFrame = null; | ||
| private boolean mListening = false; | ||
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| public static class Config { | ||
| public final int minIndexForVisible; | ||
| public final @Nullable Integer autoScrollToTopThreshold; | ||
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| Config(int minIndexForVisible, @Nullable Integer autoScrollToTopThreshold) { | ||
| this.minIndexForVisible = minIndexForVisible; | ||
| this.autoScrollToTopThreshold = autoScrollToTopThreshold; | ||
| } | ||
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| static Config fromReadableMap(ReadableMap value) { | ||
| int minIndexForVisible = value.getInt("minIndexForVisible"); | ||
| Integer autoScrollToTopThreshold = | ||
| value.hasKey("autoscrollToTopThreshold") | ||
| ? value.getInt("autoscrollToTopThreshold") | ||
| : null; | ||
| return new Config(minIndexForVisible, autoScrollToTopThreshold); | ||
| } | ||
| } | ||
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| public MaintainVisibleScrollPositionHelper(ScrollViewT scrollView, boolean horizontal) { | ||
| mScrollView = scrollView; | ||
| mHorizontal = horizontal; | ||
| } | ||
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| public void setConfig(@Nullable Config config) { | ||
| mConfig = config; | ||
| } | ||
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| /** Start listening to view hierarchy updates. Should be called when this is created. */ | ||
| public void start() { | ||
| if (mListening) { | ||
| return; | ||
| } | ||
| mListening = true; | ||
| getUIManagerModule().addUIManagerEventListener(this); | ||
| } | ||
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| /** Stop listening to view hierarchy updates. Should be called before this is destroyed. */ | ||
| public void stop() { | ||
| if (!mListening) { | ||
| return; | ||
| } | ||
| mListening = false; | ||
| getUIManagerModule().removeUIManagerEventListener(this); | ||
| } | ||
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| /** | ||
| * Update the scroll position of the managed ScrollView. This should be called after layout has | ||
| * been updated. | ||
| */ | ||
| public void updateScrollPosition() { | ||
| if (mConfig == null || mFirstVisibleView == null || mPrevFirstVisibleFrame == null) { | ||
| return; | ||
| } | ||
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| View firstVisibleView = mFirstVisibleView.get(); | ||
| Rect newFrame = new Rect(); | ||
| firstVisibleView.getHitRect(newFrame); | ||
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| if (mHorizontal) { | ||
| int deltaX = newFrame.left - mPrevFirstVisibleFrame.left; | ||
| if (deltaX != 0) { | ||
| int scrollX = mScrollView.getScrollX(); | ||
| mScrollView.scrollTo(scrollX + deltaX, mScrollView.getScrollY()); | ||
| mPrevFirstVisibleFrame = newFrame; | ||
| if (mConfig.autoScrollToTopThreshold != null | ||
| && scrollX <= mConfig.autoScrollToTopThreshold) { | ||
| mScrollView.reactSmoothScrollTo(0, mScrollView.getScrollY()); | ||
| } | ||
| } | ||
| } else { | ||
| int deltaY = newFrame.top - mPrevFirstVisibleFrame.top; | ||
| if (deltaY != 0) { | ||
| int scrollY = mScrollView.getScrollY(); | ||
| mScrollView.scrollTo(mScrollView.getScrollX(), scrollY + deltaY); | ||
| mPrevFirstVisibleFrame = newFrame; | ||
| if (mConfig.autoScrollToTopThreshold != null | ||
| && scrollY <= mConfig.autoScrollToTopThreshold) { | ||
| mScrollView.reactSmoothScrollTo(mScrollView.getScrollX(), 0); | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| private @Nullable ReactViewGroup getContentView() { | ||
| return (ReactViewGroup) mScrollView.getChildAt(0); | ||
| } | ||
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| private UIManager getUIManagerModule() { | ||
| return Assertions.assertNotNull( | ||
| UIManagerHelper.getUIManager( | ||
| (ReactContext) mScrollView.getContext(), | ||
| ViewUtil.getUIManagerType(mScrollView.getId()))); | ||
| } | ||
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| private void computeTargetView() { | ||
| if (mConfig == null) { | ||
| return; | ||
| } | ||
| ReactViewGroup contentView = getContentView(); | ||
| if (contentView == null) { | ||
| return; | ||
| } | ||
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| int currentScroll = mHorizontal ? mScrollView.getScrollX() : mScrollView.getScrollY(); | ||
| for (int i = mConfig.minIndexForVisible; i < contentView.getChildCount(); i++) { | ||
| View child = contentView.getChildAt(i); | ||
| float position = mHorizontal ? child.getX() : child.getY(); | ||
| if (position > currentScroll || i == contentView.getChildCount() - 1) { | ||
| mFirstVisibleView = new WeakReference<>(child); | ||
| Rect frame = new Rect(); | ||
| child.getHitRect(frame); | ||
| mPrevFirstVisibleFrame = frame; | ||
| break; | ||
| } | ||
| } | ||
| } | ||
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| // UIManagerListener | ||
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| @Override | ||
| public void willDispatchViewUpdates(final UIManager uiManager) { | ||
| UiThreadUtil.runOnUiThread( | ||
| new Runnable() { | ||
| @Override | ||
| public void run() { | ||
| computeTargetView(); | ||
| } | ||
| }); | ||
| } | ||
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| @Override | ||
| public void didDispatchMountItems(UIManager uiManager) { | ||
| // noop | ||
| } | ||
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| @Override | ||
| public void didScheduleMountItems(UIManager uiManager) { | ||
| // noop | ||
| } | ||
| } |
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