[bugfix] Tabs：回滚使用IntersectionObserver实现的sticky效果

example/pages/tab/index.js

@@ -25,5 +25,11 @@ Page({
       title: `点击标签 ${event.detail.index + 1}`,
       icon: 'none'
     });
+  },
+
+  onPageScroll(event) {
+    this.setData({
+      scrollTop: event.scrollTop
+    });
   }
 });

example/pages/tab/index.wxml

@@ -87,7 +87,7 @@
 </demo-block>
 
 <demo-block title="粘性布局">
-  <van-tabs sticky>
+  <van-tabs sticky scroll-top="{{ scrollTop }}">
     <van-tab
       wx:for="1234"
       wx:key="index"
@@ -107,7 +107,7 @@
       wx:key="index"
       title="{{ '标签' + item }}"
     >
-      <view class="content">
+      <view class="content" style="height: 400px;">
         {{ '内容' + item }}
       </view>
     </van-tab>

packages/tabs/index.ts

@@ -67,6 +67,10 @@ VantComponent({
     offsetTop: {
       type: Number,
       value: 0
+    },
+    scrollTop: {
+      type: Number,
+      value: 0
     }
   },
 
@@ -91,6 +95,7 @@ VantComponent({
     lineHeight: 'setLine',
     active: 'setActiveTab',
     animated: 'setTrack',
+    scrollTop: 'onScroll',
     offsetTop: 'setWrapStyle'
   },
 
@@ -102,8 +107,6 @@ VantComponent({
     this.setLine();
     this.setTrack();
     this.scrollIntoView();
-    this.observerTabScroll();
-    this.observerContentScroll();
   },
 
   destroyed() {
@@ -319,55 +322,39 @@ VantComponent({
       });
     },
 
-    observerTabScroll() {
+    // adjust tab position
+    onScroll(scrollTop) {
       if (!this.data.sticky) return;
 
       const { offsetTop } = this.data;
-      wx.createIntersectionObserver(this, {
-        thresholds: [1]
-      }).relativeToViewport().observe('.van-tabs', result => {
-        const { top } = result.boundingClientRect;
-        let position = '';
 
-        if (offsetTop > top) {
-          position = 'top';
-        }
+      this.getRect('.van-tabs').then(rect => {
+        const { top, height } = rect;
 
-        this.$emit('scroll', {
-          scrollTop: top + offsetTop,
-          isFixed: position === 'top'
+        this.getRect('.van-tabs__wrap').then(rect => {
+          const { height: wrapHeight } = rect;
+          let position = '';
+
+          if (offsetTop > top + height - wrapHeight) {
+            position = 'bottom';
+          } else if (offsetTop > top) {
+            position = 'top';
+          }
+
+          this.$emit('scroll', {
+            scrollTop: scrollTop + offsetTop,
+            isFixed: position === 'top'
+          });
+
+          if (position !== this.data.position) {
+            this.set({
+              position
+            }, () => {
+              this.setWrapStyle();
+            });
+          }
         });
-
-        this.setPosition(position);
       });
-    },
-
-    observerContentScroll() {
-      if (!this.data.sticky) return;
-
-      const { offsetTop } = this.data;
-      wx.createIntersectionObserver(this).relativeToViewport().observe('.van-tabs__content', result => {
-        const { top } = result.boundingClientRect;
-        let position = '';
-
-        if (result.intersectionRatio <= 0) {
-          position = 'bottom';
-        } else if (offsetTop > top) {
-          position = 'top';
-        }
-
-        this.setPosition(position);
-      });
-    },
-
-    setPosition(position) {
-      if (position !== this.data.position) {
-        this.set({
-          position
-        }, () => {
-          this.setWrapStyle();
-        });
-      }
     }
   }
 });