fix(ui): 拖动松手从手指位置平滑契合到目标 tab

- 拖动状态与位置状态分离
- 松手先恢复过渡但保留手指位置，下一帧再吸附到目标 tab，避免从旧位置跳变

dist/custom-tab-bar/index.js

@@ -1 +1 @@
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src/custom-tab-bar/index.tsx

@@ -41,6 +41,8 @@ export default function CustomTabBar() {
   // 微信自定义 tabBar 不会自动感知 page 路由变化，用 state 保持选中态响应式
   const [activeTab, setActiveTab] = useState<string>(currentTabPath)
   const [dragPercent, setDragPercent] = useState<number | null>(null)
+  const [isDragging, setIsDragging] = useState<boolean>(false)
+  const isDraggingRef = useRef<boolean>(false)
   const dragPercentRef = useRef<number | null>(null)
   const startXRef = useRef<number>(0)
   const barFrameRef = useRef<{ left: number; width: number } | null>(null)
@@ -105,6 +107,8 @@ export default function CustomTabBar() {
     const frame = getTabBarFrame(Taro.getSystemInfoSync().windowWidth)
     barFrameRef.current = frame
     startXRef.current = touch.clientX
+    isDraggingRef.current = false
+    setIsDragging(false)
     dragPercentRef.current = null
     setDragPercent(null)
   }
@@ -113,8 +117,10 @@ export default function CustomTabBar() {
     const frame = barFrameRef.current
     const touch = e.touches && e.touches[0]
     if (!frame || !touch) return
-    if (dragPercentRef.current === null && !hasDragged(startXRef.current, touch.clientX, DRAG_THRESHOLD_PX)) {
+    if (!isDraggingRef.current) {
-      return
+      if (!hasDragged(startXRef.current, touch.clientX, DRAG_THRESHOLD_PX)) return
+      isDraggingRef.current = true
+      setIsDragging(true)
     }
     const nextPercent = clampPercent(((touch.clientX - frame.left) / frame.width) * 100)
     dragPercentRef.current = nextPercent
@@ -125,8 +131,14 @@ export default function CustomTabBar() {
     const frame = barFrameRef.current
     if (!frame) return
     let targetIndex: number
-    if (dragPercentRef.current !== null) {
+    if (isDraggingRef.current) {
-      targetIndex = tabIndexAtPercent(dragPercentRef.current, TABS.length)
+      targetIndex = tabIndexAtPercent(dragPercentRef.current ?? 0, TABS.length)
+      isDraggingRef.current = false
+      setIsDragging(false)
+      Taro.nextTick(() => {
+        dragPercentRef.current = null
+        setDragPercent(null)
+      })
     } else {
       const touch = e.changedTouches && e.changedTouches[0]
       const x = touch ? touch.clientX : startXRef.current
@@ -136,13 +148,13 @@ export default function CustomTabBar() {
     if (target && target.pagePath !== activeTab) switchTab(target.pagePath)
     barFrameRef.current = null
     startXRef.current = 0
-    dragPercentRef.current = null
-    setDragPercent(null)
   }
 
   const cancelDrag = () => {
     barFrameRef.current = null
     startXRef.current = 0
+    isDraggingRef.current = false
+    setIsDragging(false)
     dragPercentRef.current = null
     setDragPercent(null)
   }
@@ -163,7 +175,7 @@ export default function CustomTabBar() {
         <View className='tab-bar-caustic' />
         <View className='tab-bar-rim' />
         <View
-          className={`tab-indicator ${dragPercent !== null ? 'dragging' : ''}`}
+          className={`tab-indicator ${isDragging ? 'dragging' : ''}`}
           style={{ left: dragPercent === null ? `${(activeIndex + 0.5) * TAB_CENTER_STEP}%` : `${dragPercent}%` }}
         />
         {TABS.map((tab) => {

tools/custom-tab-bar.test.mjs

@@ -1,7 +1,12 @@
 import test from 'node:test'
 import assert from 'node:assert/strict'
+import { readFileSync } from 'node:fs'
+import { fileURLToPath } from 'node:url'
+import path from 'node:path'
 import { clampPercent, getTabBarFrame, hasDragged, tabIndexAtPercent } from '../src/custom-tab-bar/tabBarGeometry.js'
 
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..')
+
 test('maps a drag percent to the tab under the finger', () => {
   assert.equal(tabIndexAtPercent(10, 5), 0)
   assert.equal(tabIndexAtPercent(30, 5), 1)
@@ -28,3 +33,11 @@ test('derives the floating bar frame from window width', () => {
   assert.deepEqual(getTabBarFrame(375), { left: 18, width: 339 })
   assert.deepEqual(getTabBarFrame(750), { left: 36, width: 678 })
 })
+
+test('enables the slide transition before snapping the indicator to the target', () => {
+  const source = readFileSync(path.join(root, 'src/custom-tab-bar/index.tsx'), 'utf8')
+  assert.match(
+    source,
+    /isDraggingRef\.current = false\s+setIsDragging\(false\)\s+Taro\.nextTick\(\(\) => \{[\s\S]*?setDragPercent\(null\)/
+  )
+})