1 files changed, 62 insertions, 5 deletions
diff --git a/src/view/com/pager/Pager.tsx b/src/view/com/pager/Pager.tsx
index 39ba29bda..531a41ee2 100644
--- a/src/view/com/pager/Pager.tsx
+++ b/src/view/com/pager/Pager.tsx
@@ -1,6 +1,10 @@
 import React, {forwardRef} from 'react'
 import {Animated, View} from 'react-native'
-import PagerView, {PagerViewOnPageSelectedEvent} from 'react-native-pager-view'
+import PagerView, {
+  PagerViewOnPageSelectedEvent,
+  PagerViewOnPageScrollEvent,
+  PageScrollStateChangedNativeEvent,
+} from 'react-native-pager-view'
 import {s} from 'lib/styles'
 
 export type PageSelectedEvent = PagerViewOnPageSelectedEvent
@@ -21,6 +25,7 @@ interface Props {
   initialPage?: number
   renderTabBar: RenderTabBarFn
   onPageSelected?: (index: number) => void
+  onPageSelecting?: (index: number) => void
   testID?: string
 }
 export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
@@ -31,11 +36,15 @@ export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
       initialPage = 0,
       renderTabBar,
       onPageSelected,
+      onPageSelecting,
       testID,
     }: React.PropsWithChildren<Props>,
     ref,
   ) {
     const [selectedPage, setSelectedPage] = React.useState(0)
+    const lastOffset = React.useRef(0)
+    const lastDirection = React.useRef(0)
+    const scrollState = React.useRef('')
     const pagerView = React.useRef<PagerView>(null)
 
     React.useImperativeHandle(ref, () => ({
@@ -50,15 +59,61 @@ export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
       [setSelectedPage, onPageSelected],
     )
 
+    const onPageScroll = React.useCallback(
+      (e: PagerViewOnPageScrollEvent) => {
+        const {position, offset} = e.nativeEvent
+        if (offset === 0) {
+          // offset hits 0 in some awkward spots so we ignore it
+          return
+        }
+        // NOTE
+        // we want to call `onPageSelecting` as soon as the scroll-gesture
+        // enters the "settling" phase, which means the user has released it
+        // we can't infer directionality from the scroll information, so we
+        // track the offset changes. if the offset delta is consistent with
+        // the existing direction during the settling phase, we can say for
+        // certain where it's going and can fire
+        // -prf
+        if (scrollState.current === 'settling') {
+          if (lastDirection.current === -1 && offset < lastOffset.current) {
+            onPageSelecting?.(position)
+            lastDirection.current = 0
+          } else if (
+            lastDirection.current === 1 &&
+            offset > lastOffset.current
+          ) {
+            onPageSelecting?.(position + 1)
+            lastDirection.current = 0
+          }
+        } else {
+          if (offset < lastOffset.current) {
+            lastDirection.current = -1
+          } else if (offset > lastOffset.current) {
+            lastDirection.current = 1
+          }
+        }
+        lastOffset.current = offset
+      },
+      [lastOffset, lastDirection, onPageSelecting],
+    )
+
+    const onPageScrollStateChanged = React.useCallback(
+      (e: PageScrollStateChangedNativeEvent) => {
+        scrollState.current = e.nativeEvent.pageScrollState
+      },
+      [scrollState],
+    )
+
     const onTabBarSelect = React.useCallback(
       (index: number) => {
         pagerView.current?.setPage(index)
+        onPageSelecting?.(index)
       },
-      [pagerView],
+      [pagerView, onPageSelecting],
     )
 
     return (
-      <View testID={testID}>
+      <View testID={testID} style={s.flex1}>
         {tabBarPosition === 'top' &&
           renderTabBar({
             selectedPage,
@@ -66,9 +121,11 @@ export const Pager = forwardRef<PagerRef, React.PropsWithChildren<Props>>(
           })}
         <AnimatedPagerView
           ref={pagerView}
-          style={s.h100pct}
+          style={s.flex1}
           initialPage={initialPage}
-          onPageSelected={onPageSelectedInner}>
+          onPageScrollStateChanged={onPageScrollStateChanged}
+          onPageSelected={onPageSelectedInner}
+          onPageScroll={onPageScroll}>
           {children}
         </AnimatedPagerView>
         {tabBarPosition === 'bottom' &&