fix: SlideToConfirm snap-to-end — trackWidthRef+State, no _value/_offset private API, layout guard

components/SlideToConfirm.tsx

@@ -2,10 +2,12 @@
  * SlideToConfirm — pure RN, no RNGH, no Reanimated.
  * PanResponder on handle + Animated(useNativeDriver:false).
  *
- * Fix: live refs break stale closures — disabledRef + onConfirmRef
- * updated on every render so PanResponder always reads current values.
+ * Fix history:
+ * - v1: stale closure fix — disabledRef + onConfirmRef
+ * - v2: trackWidth=0 snap bug — trackWidthRef+State, startPos/currentPos refs,
+ *       eliminated _value/_offset private API, layout guard on gesture start
  */
-import { useRef } from 'react';
+import { useRef, useState } from 'react';
 import {
   Animated,
   PanResponder,
@@ -23,89 +25,132 @@ interface Props {
   color?: string;
 }
 
-const HANDLE_SIZE = 56;
-const THRESHOLD   = 0.80;
+const HANDLE_SIZE   = 56;
+const HANDLE_MARGIN = 3;
+const THRESHOLD     = 0.80;
 
 export function SlideToConfirm({ onConfirm, label = 'Slide to confirm', disabled = false, style, color }: Props) {
-  const trackWidth = useRef(0);
-  const confirmed  = useRef(false);
-  const translateX = useRef(new Animated.Value(0)).current;
+  // trackWidthRef — read inside PanResponder (no stale closure)
+  // trackWidthState — triggers re-render so labelOpacity interpolation updates
+  const trackWidthRef   = useRef(0);
+  const [trackWidthState, setTrackWidthState] = useState(0);
 
-  // ── Live refs: break stale closures inside PanResponder ──────────────────
+  const confirmed   = useRef(false);
+  const translateX  = useRef(new Animated.Value(0)).current;
+
+  // Explicit position tracking — avoids private _value/_offset API
+  const startPos    = useRef(0);   // handle position when gesture starts
+  const currentPos  = useRef(0);   // handle position during/after gesture
+
+  // ── Live refs: break stale closures ──────────────────────────────────────
   const disabledRef  = useRef(disabled);
-  disabledRef.current = disabled;          // updated on every render
+  disabledRef.current = disabled;
   const onConfirmRef = useRef(onConfirm);
-  onConfirmRef.current = onConfirm;        // updated on every render
+  onConfirmRef.current = onConfirm;
 
   const panResponder = useRef(
     PanResponder.create({
-      onStartShouldSetPanResponder: () => !disabledRef.current,
-      // Horizontal-dominance check prevents ScrollView stealing vertical-ish drags on iOS
+      // Block gestures until layout has been measured
+      onStartShouldSetPanResponder: () =>
+        !disabledRef.current && trackWidthRef.current > 0,
+      // Horizontal-dominance — prevents ScrollView stealing on iOS
       onMoveShouldSetPanResponder: (_, gs) =>
-        !disabledRef.current && Math.abs(gs.dx) > Math.abs(gs.dy) * 2,
+        !disabledRef.current &&
+        trackWidthRef.current > 0 &&
+        Math.abs(gs.dx) > Math.abs(gs.dy) * 2,
+
       onPanResponderGrant: () => {
         confirmed.current = false;
-        (translateX as any).setOffset((translateX as any)._value);
-        translateX.setValue(0);
+        // Stop any running spring before starting a new drag
+        translateX.stopAnimation();
+        startPos.current = currentPos.current;
       },
+
       onPanResponderMove: (_, gs) => {
-        const maxX    = Math.max(trackWidth.current - HANDLE_SIZE - 6, 1);
-        const clamped = Math.min(Math.max(gs.dx, 0), maxX);
-        translateX.setValue(clamped - (translateX as any)._offset);
+        const maxX = trackWidthRef.current - HANDLE_SIZE - HANDLE_MARGIN * 2;
+        if (maxX <= 0) return; // safety — layout not ready
+
+        const raw     = startPos.current + gs.dx;
+        const clamped = Math.min(Math.max(raw, 0), maxX);
+        currentPos.current = clamped;
+        translateX.setValue(clamped);
 
         if (!confirmed.current && clamped / maxX >= THRESHOLD) {
           confirmed.current = true;
-          (translateX as any).flattenOffset();
           Animated.spring(translateX, {
             toValue: maxX,
             useNativeDriver: false,
             damping: 18,
             stiffness: 220,
-          }).start();
-          onConfirmRef.current();   // always calls latest onConfirm
+          }).start(({ finished }) => {
+            if (finished) currentPos.current = maxX;
+          });
+          onConfirmRef.current();
         }
       },
+
       onPanResponderRelease: () => {
-        (translateX as any).flattenOffset();
         if (!confirmed.current) {
+          currentPos.current = 0;
           Animated.spring(translateX, {
             toValue: 0,
             useNativeDriver: false,
             damping: 18,
             stiffness: 220,
-          }).start();
+          }).start(({ finished }) => {
+            if (finished) currentPos.current = 0;
+          });
         }
       },
+
       onPanResponderTerminate: () => {
-        (translateX as any).flattenOffset();
         if (!confirmed.current) {
+          currentPos.current = 0;
           Animated.spring(translateX, {
             toValue: 0,
             useNativeDriver: false,
-          }).start();
+          }).start(({ finished }) => {
+            if (finished) currentPos.current = 0;
+          });
         }
       },
     })
   ).current;
 
-  const maxXForOpacity = Math.max(trackWidth.current - HANDLE_SIZE - 6, 1);
+  const maxXForOpacity = Math.max(trackWidthState - HANDLE_SIZE - HANDLE_MARGIN * 2, 1);
   const labelOpacity = translateX.interpolate({
-    inputRange:  [0, maxXForOpacity > 0 ? maxXForOpacity * 0.6 : 1],
+    inputRange:  [0, maxXForOpacity * 0.6],
     outputRange: [1, 0],
     extrapolate: 'clamp',
   });
 
   return (
     <View
-      style={[styles.track, disabled && styles.trackDisabled, color && !disabled ? { backgroundColor: color } : undefined, style]}
-      onLayout={e => { trackWidth.current = e.nativeEvent.layout.width; }}
+      style={[
+        styles.track,
+        disabled && styles.trackDisabled,
+        color && !disabled ? { backgroundColor: color } : undefined,
+        style,
+      ]}
+      onLayout={e => {
+        const w = e.nativeEvent.layout.width;
+        trackWidthRef.current = w;   // PanResponder reads this
+        setTrackWidthState(w);       // triggers re-render for labelOpacity
+      }}
     >
-      <Animated.View style={[StyleSheet.absoluteFill, styles.labelWrap, { opacity: labelOpacity }]} pointerEvents="none">
+      <Animated.View
+        style={[StyleSheet.absoluteFill, styles.labelWrap, { opacity: labelOpacity }]}
+        pointerEvents="none"
+      >
         <Text style={styles.label}>{label}</Text>
       </Animated.View>
 
       <Animated.View
-        style={[styles.handle, disabled && styles.handleDisabled, { transform: [{ translateX }] }]}
+        style={[
+          styles.handle,
+          disabled && styles.handleDisabled,
+          { transform: [{ translateX }] },
+        ]}
         {...panResponder.panHandlers}
         collapsable={false}
       >
@@ -138,7 +183,7 @@ const styles = StyleSheet.create({
     backgroundColor: '#fff',
     alignItems: 'center',
     justifyContent: 'center',
-    marginLeft: 3,
+    marginLeft: HANDLE_MARGIN,
     shadowColor: '#000',
     shadowOffset: { width: 0, height: 2 },
     shadowOpacity: 0.18,