fix: fixed a computed error

fix #291, fix #294

Author: dohooo

src/hooks/computeNewIndexWhenDataChanges.ts

@@ -1,3 +1,11 @@
+export function omitZero(a: number, b: number) {
+  "worklet";
+  if (a === 0)
+    return 0;
+
+  return b;
+}
+
 export function computeNewIndexWhenDataChanges(params: {
   direction: number
   handlerOffset: number
@@ -16,14 +24,15 @@ export function computeNewIndexWhenDataChanges(params: {
 
   if (isPositive) {
     positionIndex = (Math.abs(handlerOffset)) / size;
-    round = parseInt(String(positionIndex / previousLength));
+    round = parseInt(String(omitZero(previousLength, positionIndex / previousLength)));
   }
   else {
     positionIndex = (Math.abs(handlerOffset) - size) / size;
-    round = parseInt(String(positionIndex / previousLength)) + 1;
+    round = parseInt(String(omitZero(previousLength, positionIndex / previousLength))) + 1;
   }
 
-  const prevIndex = isPositive ? (positionIndex) % previousLength : previousLength - (positionIndex) % previousLength - 1;
+  const prevOffset = omitZero(previousLength, positionIndex % previousLength);
+  const prevIndex = isPositive ? prevOffset : previousLength - prevOffset - 1;
   const changedLength = round * (currentLength - previousLength);
   const changedOffset = changedLength * size;
   if (prevIndex > currentLength - 1 && currentLength < previousLength) {

src/hooks/index.test.ts

@@ -68,4 +68,15 @@ describe("should work as expected", () => {
 
     expect(handlerOffset / size).toBe(4 * negative);
   });
+
+  it("Changing length of data set from 0 to 3, the index remains original.", async () => {
+    const handlerOffset = computeNewIndexWhenDataChanges(params({
+      currentIndex: 0,
+      direction: "positive",
+      previousLength: 0,
+      currentLength: 3,
+    }));
+
+    expect(handlerOffset / size).toBe(0 * positive);
+  });
 });

src/hooks/useCommonVariables.ts

@@ -37,14 +37,19 @@ export function useCommonVariables(
   }, [vertical, handlerOffset, defaultHandlerOffsetValue]);
 
   useAnimatedReaction(() => {
+    const _data = data.slice();
     const previousLength = prevData.value.length;
-    const currentLength = data.length;
+    const currentLength = _data.length;
     const isLengthChanged = previousLength !== currentLength;
+    const shouldComputed = isLengthChanged && loop;
+
+    if (shouldComputed)
+      prevData.value = _data;
+
     return {
-      shouldComputed: isLengthChanged && loop,
+      shouldComputed,
       previousLength,
       currentLength,
-      data,
     };
   }, ({ shouldComputed, previousLength, currentLength }) => {
     if (shouldComputed) {
@@ -58,12 +63,8 @@ export function useCommonVariables(
         size,
         handlerOffset: handlerOffset.value,
       });
-
-      prevData.value = data;
     }
-  }, [
-    data, loop,
-  ]);
+  }, [data, loop]);
 
   return {
     size,