我的需求是多选，不管年级如何切换，只要是选择过的班级，最终拿到所有id

<view class="sold_cents">
  <view class="grade_data flex">
    <view class="flex bot_grade">
      <view>年级</view>
      <view>班级</view>
    </view>
    <view class="flex grade_cent">
      <view class="grade_cent_left">
        <view wx:for="{{items}}" wx:key="index" data-index="{{index}}"
          class="fanwei_check fanwei_left flex {{checkbox_index==index?'checked_class':''}}" data-id="{{item.id}}"
          bindtap="click_checkbox">
          <label>
            <view class="fanwei_check_left">
              {{item.title}}
            </view>
          </label>
          <view class="fanwei_check_right">
            <image mode="widthFix" src="/image/img76.png"></image>
          </view>
        </view>
      </view>
      <view>
        <view class="fanwei_check flex" wx:for="{{items_child}}" wx:key="index">
          <view class="fanwei_check_left flex" data-id="{{item.id}}" bindtap="checkboxChange">
            <image mode="widthFix" src="/image/img71.png" hidden="{{item.checked}}"></image>
            <image mode="widthFix" src="/image/img72.png" hidden="{{!item.checked}}"></image>
            <view>{{item.title}}</view>
          </view>
        </view>
      </view>
    </view>
  </view>
</view>

page{
    background: cornflowerblue;
}
.flex{
    display: flex;
}
.sold_cents {
    width: 100%;
    height: 750rpx;
    background: #FFFFFF;
    border-radius: 40rpx 40rpx 0px 0px;
    position: fixed;
    left: 0;
    bottom: 0;
    z-index: 5;
  }
.bot_grade {
    border-bottom: 1px solid #F2F2F2;
    padding: 18rpx 0 22rpx 0;
  }
  .bot_grade>view {
    width: 50%;
    text-align: center;
    font-size: 32rpx;
    font-weight: 500;
    color: #333333;
  }
  .grade_cent>view{
    width: 50%;
  }
  .grade_cent_left{
    background-color: #F9F9F9;
  }
  .grade_data{
    width: 100%;height: 100%;flex-direction: column;
  }
  .grade_cent{
    flex: 1;
  }
  .fanwei_check{
    padding: 30rpx;
  }
  .fanwei_check_right image{
    width: 15rpx;
    margin-left: 30rpx;
  }
  .hidden_checkbox{
    display: none;
  }
  .fanwei_left{
    justify-content: center;
    align-items: center;
  }
  .checked_class{
    background-color: #FFFFFF;
  }
  .fanwei_check_left image{
    width: 40rpx;margin-right: 20rpx;
  }

Page({
  data: {
    checkbox_index: 0,
    items: [{
      child: [
        {
          checked: false,
          id: 1,
          title: "1班级",
          type: 3
        },
        {
          checked: false,
          id: 2,
          title: "1班级",
          type: 3
        }
      ],
      id: 3,
      title: "2021级",
      type: 2
    }, {
      child: [
        {
          checked: false,
          id: 4,
          title: "3班级",
          type: 3
        },
        {
          checked: false,
          id: 5,
          title: "4班级",
          type: 3
        }
      ],
      id: 6,
      title: "2022级",
      type: 2
    }, {
      child: [
        {
          checked: false,
          id: 7,
          title: "5班级",
          type: 3
        },
        {
          checked: false,
          id: 8,
          title: "FF班级",
          type: 3
        }
      ],
      id: 9,
      title: "2023级",
      type: 2
    }],//所有范围数据
    items_child: [],//当前展示的班级数据  默认显示第一个年级的班级数据
    all_child: [] //最终提交的所有班级id
  },
  click_checkbox(e) {
    // 年级
    let that = this;
    let index = e.currentTarget.dataset.index;
    that.setData({
      checkbox_index: index,
      items_child: that.data.items[index].child  //显示当前年级的班级数据
    });
  },
  checkboxChange(e) {
    let that = this;
    let all_child_val = that.data.all_child;
    let id = e.currentTarget.dataset.id;
    if (all_child_val.includes(id)) {
      // 包含这个id 删除这个id 取消
      all_child_val.splice(all_child_val.findIndex(item => item === id), 1)
    } else {
      // 不包含id  添加这个id 新增
      all_child_val.push(id);
    }
    that.setData({
      all_child: all_child_val
    });

    console.log("当前选中的值", that.data.all_child)

    // 拿最终选中的值去找当前展示的数组，更改checked的状态
    let items_child_val = that.data.items_child;
    for (let k = 0; k < that.data.items_child.length; k++) {
      let id_val = that.data.items_child[k].id;
      if (all_child_val.includes(id_val)) {
        var checked_type = "items_child[" + k + "].checked";
        console.log("000", checked_type)
        that.setData({
          [checked_type]: true
        });
      } else {
        var checked_type = "items_child[" + k + "].checked";
        console.log("000", checked_type)
        that.setData({
          [checked_type]: false
        });
      }
    }
  }
})