fix: 修复 ImagePreview 无法动态设置 startPosition 的问题 (#562)

Author: 3lang3

packages/react-vant/src/components/image-preview/ImagePreview.tsx

@@ -37,7 +37,7 @@ const ImagePreview = React.forwardRef<ImagePreviewRef, ImagePreviewProps>(
         {props.images && (
           <Slides
             ref={slidesRef}
-            defaultIndex={active}
+            defaultIndex={props.startPosition}
             onIndexChange={onSwipeChange}
             images={props.images}
             onTap={() => {

packages/react-vant/src/components/image-preview/slides.tsx

@@ -5,6 +5,7 @@ import { Slide } from './slide'
 import { bound } from '../utils/bound'
 import { createNamespace, unitToPx } from '../utils'
 import clsx from 'clsx'
+import { useUpdateEffect } from '../hooks'
 
 export type SlidesType = {
   images: string[]
@@ -29,6 +30,10 @@ export const Slides = forwardRef<SlidesRef, SlidesType>((props, ref) => {
 
   const count = props.images.length
 
+  useUpdateEffect(() => {
+    swipeTo(props.defaultIndex, true)
+  }, [props.defaultIndex])
+
   function swipeTo(index: number, immediate = false) {
     const i = bound(index, 0, count - 1)
     props.onIndexChange?.(i)