From 0080e9c26e80f44d2d9c4fe30045b4bad1c2a4a7 Mon Sep 17 00:00:00 2001
From: TsMask <340112800@qq.com>
Date: Tue, 3 Sep 2024 11:00:00 +0800
Subject: [PATCH] =?UTF-8?q?feat:=20=E5=85=AC=E5=85=B1=E7=BB=84=E4=BB=B6-?=
 =?UTF-8?q?=E8=99=9A=E6=8B=9F=E6=BB=9A=E5=8A=A8=E5=88=97=E8=A1=A8?=
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---
 src/components/VirtualList/index.vue | 204 +++++++++++++++++++++++++++
 1 file changed, 204 insertions(+)
 create mode 100644 src/components/VirtualList/index.vue

diff --git a/src/components/VirtualList/index.vue b/src/components/VirtualList/index.vue
new file mode 100644
index 00000000..63e003e8
--- /dev/null
+++ b/src/components/VirtualList/index.vue
@@ -0,0 +1,204 @@
+<script lang="ts" setup>
+import { reactive, ref, computed, unref, onUpdated, watchEffect } from 'vue';
+
+const props = defineProps({
+  /**列表高度 */
+  height: {
+    type: Number,
+    default: 300,
+  },
+  /**列表项高度 */
+  itemHeight: {
+    type: Number,
+    default: 30,
+  },
+  /**数据 */
+  data: {
+    type: Array,
+    default: () => [],
+  },
+  /**预先兜底缓存数量 */
+  cache: {
+    type: Number,
+    default: 2,
+  },
+  /**是否动态加载 */
+  dynamic: {
+    type: Boolean,
+    default: false,
+  },
+});
+
+const state = reactive<any>({
+  start: 0,
+  end: 10,
+  scrollOffset: 0,
+  cacheData: [],
+});
+const virtualListRef = ref();
+
+const getWrapperStyle = computed(() => {
+  const { height } = props;
+  return {
+    height: `${height}px`,
+  };
+});
+
+const getInnerStyle = computed(() => {
+  return {
+    height: `${unref(getTotalHeight)}px`,
+    width: '100%',
+  };
+});
+
+const getListStyle = computed(() => {
+  return {
+    willChange: 'transform',
+    transform: `translateY(${state.scrollOffset}px)`,
+  };
+});
+
+// 数据数量
+const total = computed(() => {
+  return props.data.length;
+});
+
+// 总体高度
+const getTotalHeight = computed(() => {
+  if (!props.dynamic) return unref(total) * props.itemHeight;
+  return getCurrentTop(unref(total));
+});
+
+// 当前屏幕显示的数量
+const clientCount = computed(() => {
+  return Math.ceil(props.height / props.itemHeight);
+});
+
+// 当前屏幕显示的数据
+const clientData = computed(() => {
+  return props.data.slice(state.start, state.end);
+});
+
+const onScroll = (e: any) => {
+  const { scrollTop } = e.target;
+  if (state.scrollOffset === scrollTop) return;
+  const { cache, dynamic, itemHeight } = props;
+  const cacheCount = Math.max(1, cache);
+
+  let startIndex = dynamic
+    ? getStartIndex(scrollTop)
+    : Math.floor(scrollTop / itemHeight);
+
+  const endIndex = Math.max(
+    0,
+    Math.min(unref(total), startIndex + unref(clientCount) + cacheCount)
+  );
+
+  if (startIndex > cacheCount) {
+    startIndex = startIndex - cacheCount;
+  }
+
+  // 偏移量
+  const offset = dynamic
+    ? getCurrentTop(startIndex)
+    : scrollTop - (scrollTop % itemHeight);
+
+  Object.assign(state, {
+    start: startIndex,
+    end: endIndex,
+    scrollOffset: offset,
+  });
+};
+
+// 二分法去查找对应的index
+const getStartIndex = (scrollTop = 0): number => {
+  let low = 0;
+  let high = state.cacheData.length - 1;
+  while (low <= high) {
+    const middle = low + Math.floor((high - low) / 2);
+    const middleTopValue = getCurrentTop(middle);
+    const middleBottomValue = getCurrentTop(middle + 1);
+
+    if (middleTopValue <= scrollTop && scrollTop <= middleBottomValue) {
+      return middle;
+    } else if (middleBottomValue < scrollTop) {
+      low = middle + 1;
+    } else if (middleBottomValue > scrollTop) {
+      high = middle - 1;
+    }
+  }
+  return Math.min(
+    unref(total) - unref(clientCount),
+    Math.floor(scrollTop / props.itemHeight)
+  );
+};
+
+const getCurrentTop = (index: number) => {
+  const lastIndex = state.cacheData.length - 1;
+
+  if (Object.hasOwn(state.cacheData, index)) {
+    return state.cacheData[index].top;
+  } else if (Object.hasOwn(state.cacheData, index - 1)) {
+    return state.cacheData[index - 1].bottom;
+  } else if (index > lastIndex) {
+    return (
+      state.cacheData[lastIndex].bottom +
+      Math.max(0, index - state.cacheData[lastIndex].index) * props.itemHeight
+    );
+  } else {
+    return index * props.itemHeight;
+  }
+};
+
+onUpdated(() => {
+  if (!props.dynamic) return;
+  const childrenList = virtualListRef.value.children || [];
+  [...childrenList].forEach((node: any, index: number) => {
+    const height = node.getBoundingClientRect().height;
+    const currentIndex = state.start + index;
+    if (state.cacheData[currentIndex].height === height) return;
+
+    state.cacheData[currentIndex].height = height;
+    state.cacheData[currentIndex].top = getCurrentTop(currentIndex);
+    state.cacheData[currentIndex].bottom =
+      state.cacheData[currentIndex].top + state.cacheData[currentIndex].height;
+  });
+});
+
+watchEffect(() => {
+  clientData.value.forEach((_, index) => {
+    const currentIndex = state.start + index;
+    if (Object.hasOwn(state.cacheData, currentIndex)) return;
+    state.cacheData[currentIndex] = {
+      top: currentIndex * props.itemHeight,
+      height: props.itemHeight,
+      bottom: (currentIndex + 1) * props.itemHeight,
+      index: currentIndex,
+    };
+  });
+});
+</script>
+
+<template>
+  <div
+    class="virtual-list-wrapper"
+    ref="wrapperRef"
+    :style="getWrapperStyle"
+    @scroll="onScroll"
+  >
+    <div class="virtual-list-inner" ref="innerRef" :style="getInnerStyle">
+      <div class="virtual-list" :style="getListStyle" ref="virtualListRef">
+        <div v-for="(item, index) in clientData" :key="index + state.start">
+          <slot name="default" :item="item"></slot>
+        </div>
+      </div>
+    </div>
+  </div>
+</template>
+
+<style lang="css" scoped>
+.virtual-list-wrapper {
+  position: relative;
+  overflow-y: auto;
+}
+</style>