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import React, {useEffect, useState, useMemo} from 'react'
import {FlatList, StyleSheet, View} from 'react-native'
import {GestureDetector, Gesture} from 'react-native-gesture-handler'
import {useSharedValue, withTiming, runOnJS} from 'react-native-reanimated'
import {Selector} from './Selector'
const HEADER_ITEM = {_reactKey: '__header__'}
const SELECTOR_ITEM = {_reactKey: '__selector__'}
const STICKY_HEADER_INDICES = [1]
const SWIPE_GESTURE_MAX_DISTANCE = 200
const SWIPE_GESTURE_VEL_TRIGGER = 2000
const SWIPE_GESTURE_HIT_SLOP = {left: -50, top: 0, right: 0, bottom: 0} // we ignore the left 20 pixels to avoid conflicts with the page-nav gesture
export function ViewSelector({
sections,
items,
refreshing,
swipeEnabled,
renderHeader,
renderItem,
onSelectView,
onRefresh,
onEndReached,
}: {
sections: string[]
items: any[]
refreshing?: boolean
swipeEnabled?: boolean
renderHeader?: () => JSX.Element
renderItem: (item: any) => JSX.Element
onSelectView?: (viewIndex: number) => void
onRefresh?: () => void
onEndReached?: (info: {distanceFromEnd: number}) => void
}) {
const [selectedIndex, setSelectedIndex] = useState<number>(0)
const swipeGestureInterp = useSharedValue<number>(0)
// events
// =
const onPressSelection = (index: number) => setSelectedIndex(index)
useEffect(() => {
onSelectView?.(selectedIndex)
}, [selectedIndex])
// gestures
// =
const swipeGesture = useMemo(() => {
if (!swipeEnabled) return undefined
return Gesture.Pan()
.hitSlop(SWIPE_GESTURE_HIT_SLOP)
.onUpdate(e => {
// calculate [-1, 1] range for the gesture
const clamped = Math.min(e.translationX, SWIPE_GESTURE_MAX_DISTANCE)
const reversed = clamped * -1
const scaled = reversed / SWIPE_GESTURE_MAX_DISTANCE
swipeGestureInterp.value = scaled
})
.onEnd(e => {
const vx = e.velocityX
if (
swipeGestureInterp.value >= 0.5 ||
(vx < 0 && Math.abs(vx) > SWIPE_GESTURE_VEL_TRIGGER)
) {
// swiped to next
if (selectedIndex < sections.length - 1) {
// interp to the next item's position...
swipeGestureInterp.value = withTiming(1, {duration: 100}, () => {
// ...then update the index, which triggers the useEffect() below [1]
runOnJS(setSelectedIndex)(selectedIndex + 1)
})
} else {
swipeGestureInterp.value = withTiming(0, {duration: 100})
}
} else if (
swipeGestureInterp.value <= -0.5 ||
(vx > 0 && Math.abs(vx) > SWIPE_GESTURE_VEL_TRIGGER)
) {
// swiped to prev
if (selectedIndex > 0) {
// interp to the prev item's position...
swipeGestureInterp.value = withTiming(-1, {duration: 100}, () => {
// ...then update the index, which triggers the useEffect() below [1]
runOnJS(setSelectedIndex)(selectedIndex - 1)
})
} else {
swipeGestureInterp.value = withTiming(0, {duration: 100})
}
} else {
swipeGestureInterp.value = withTiming(0, {duration: 100})
}
})
}, [swipeEnabled, swipeGestureInterp, selectedIndex, sections.length])
useEffect(() => {
// [1] completes the swipe gesture animation by resetting the interp value
// this has to be done as an effect so that it occurs *after* the selectedIndex has been updated
swipeGestureInterp.value = 0
}, [swipeGestureInterp, selectedIndex])
// rendering
// =
const renderItemInternal = ({item}: {item: any}) => {
if (item === HEADER_ITEM) {
if (renderHeader) {
return renderHeader()
}
return <View />
} else if (item === SELECTOR_ITEM) {
return (
<Selector
items={sections}
selectedIndex={selectedIndex}
swipeGestureInterp={swipeGestureInterp}
onSelect={onPressSelection}
/>
)
} else {
return renderItem(item)
}
}
const data = [HEADER_ITEM, SELECTOR_ITEM, ...items]
const listEl = (
<FlatList
data={data}
keyExtractor={item => item._reactKey}
renderItem={renderItemInternal}
stickyHeaderIndices={STICKY_HEADER_INDICES}
refreshing={refreshing}
onRefresh={onRefresh}
onEndReached={onEndReached}
/>
)
if (swipeEnabled) {
return <GestureDetector gesture={swipeGesture}>{listEl}</GestureDetector>
}
return listEl
}
const styles = StyleSheet.create({})
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