.scrollView{
 padding: 0 20rpx;
 white-space: nowrap;
 box-sizing: border-box;
}
.item{
 display: inline-block;
 margin-right: 20rpx;
 width: calc(100% / 3);
 height: 100rpx;
 background: #ff00ff;
}

.scrollView1{
 display: flex;
 margin-top: 40rpx;
 padding: 0 20rpx;
 width: 100%;
 flex-wrap: nowrap;
 box-sizing: border-box;
}
.item1{
 margin-right: 20rpx;
 width: calc(100% / 3);
 height: 100rpx;
 background: #ff00ff;
}
.scrollView2{
 margin-top: 40rpx;
 padding: 0 20rpx;
 width: 100%;
 box-sizing: border-box;
}
.itemContainer{
 display: flex;
 width: 100%;
 flex-wrap: nowrap;
}
.scrollItem{
 margin-right: 20rpx;
}

.scrollView3{
 margin-top: 40rpx;
 padding: 0 20rpx;
 width: 100%;
 box-sizing: border-box;
}
.item3{
 margin-right: 20rpx;
 /* width: calc(100% / 3); */
 width: 240rpx;
 height: 100rpx;
 background: #aa22dd;
}

<!-- 要想使用flex布局实现横向滚动，就要在scroll-view里加一层容器包裹，并且使用子组件才会出现滚动效果 -->
<scroll-view scroll-x class="scrollView2">
 <view class="itemContainer">
  <block wx:for="{{4}}" wx:key="{{index}}">
   <view-item class="scrollItem" />
  </block>
 </view>
</scroll-view>

<scroll-view scroll-x class="scrollView">
 <block wx:for="{{4}}" wx:key="{{index}}">
  <view class="item"></view>
 </block>
</scroll-view>