最近项目里有个需求要做个滚动选择器，在网上找了半天也没找到合适的demo，没办法只能发挥我的聪明才智创造一个，不哔哔上代码。
js:
// pages/xuanzeqi/xuanzeqi.jsPage({/*** 页面的初始数据*/data: {list: ['0分', '1分', '2分', '3分', '4分', '5分', '6分', '7分', '8分', '9分', '10分', '11分', '12分', '13分', '14分', '15分', '16分', '17分', '18分', '19分', '20分', '21分', '22分', '23分', '24分', '25分', '26分', '27分', '28分', '29分', '30分', '31分', '32分', '33分', '34分', '35分', '36分', '37分', '38分', '39分', '40分', '41分', '42分', '43分', '44分', '45分', '46分', '47分', '48分', '49分', '50分', '51分', '52分', '53分', '54分', '55分', '56分', '57分', '58分', '59分'],box_height: 0,//选择器的高度（非控制项，自动计算），单位pxpicker:{ //选择器的控制变量box_width: 200,//选择器宽度，单位pxchoose_item_height: 30,//选择器中每一项选项的高度，单位pxchoose_item_font_size:25,//选择器中每一项选项字体大小，单位pxscroll_animation: true,//是否使用动画过渡choose_item_number: 13,//选择器内选项的个数(要求为单数)bgColor:'#01356f',//选择器的背景颜色choose_item_font_color:'white',//选择器选项的字体颜色},mid_item:0,scroll_into_view:'item_0',//滚动到选项的iditem_height_list:[],//存储每一项距离顶端的y轴数据picker_value:null,//选择器的值opacity_list:[],//透明阶梯cover_list: [],//遮盖层属性列表touchY: -1,scrollTop:0,},touchMove: function (e) {let that = thislet touY = e.touches[0].pageY;if(that.data.touchY == -1){that.data.touchY = touY} else{let cha = that.data.touchY - touYthat.setData({scrollTop: that.data.scrollTop + cha})that.data.touchY = touY}if (that.coverEndTimer) {clearTimeout(that.coverEndTimer);that.coverEndTimer = null;}that.coverEndTimer = setTimeout(function () {that.data.touchY = -1}, 200);},//监听选择器滚动事件bindscrollevent:function(e){let that = this// that.flashOpacity(e.detail.scrollTop)console.log(e)if (that.scrollEndTimer) {clearTimeout(that.scrollEndTimer);that.scrollEndTimer = null;}that.scrollEndTimer = setTimeout(function () {console.log("滑动结束");// that.flashOpacity(e.detail.scrollTop)that.itemToMid(e.detail.scrollTop)that.data.scrollTop = e.detail.scrollTop}, 200);},//更新透明度flashOpacity:function(e){let that = thisthat.setData({item_height_list: that.data.item_height_list})for (let i in that.data.item_height_list) {if (that.data.item_height_list[i].bottom > e && that.data.item_height_list[i].top >= e) {for(let j = 0; j < that.data.opacity_list.length; j++){if(i - (j + 1) >= 0){that.data.item_height_list[i - (j + 1)].opacity = that.data.opacity_list[j]}let a = parseInt(i)if(a + (j + 1) < that.data.list.length){that.data.item_height_list[a + (j + 1)].opacity = that.data.opacity_list[j]}}let a = parseInt(i)for (let j in that.data.item_height_list) {if (!(j >= a - that.data.opacity_list.length && j <= a + that.data.opacity_list.length)){that.data.item_height_list[j].opacity = 0}}that.setData({item_height_list: that.data.item_height_list})break;}}},//根据滚动距离滚动到选项中间itemToMid:function(e){let that = thisconsole.log("执行了",e)for (let i in that.data.item_height_list) {if (that.data.item_height_list[i].bottom > e && that.data.item_height_list[i].top <= e) {console.log(that.data.item_height_list[i].bottom, that.data.item_height_list[i].top)if (i < that.data.mid_item - 1) {that.setData({scroll_into_view: 'cushion_top_' + i})} else {console.log(parseInt(i) - that.data.mid_item + 1)that.setData({scroll_into_view: 'item_' + (parseInt(i) - that.data.mid_item + 1)})}that.setData({picker_value : that.data.list[i]})break;}}},//初始化init:function(e){let that = this//先计算该选择器的高度（根据每项高度和项目个数计算）单位px//如果选择器个数填写为双数，则强制-1变为单数if (that.data.picker.choose_item_number % 2 == 0){that.setData({['picker.choose_item_number'] : that.data.picker.choose_item_number - 1})}//通过乘积计算选择器高度that.setData({box_height : that.data.picker.choose_item_number * that.data.picker.choose_item_height})//计算选择器中间项应该是第几项that.setData({mid_item : (that.data.picker.choose_item_number + 1) / 2 })//初始化遮盖层透明阶梯透明度从（0.1到0.9）let unit = Math.round(80 / (that.data.mid_item - 1)) /**阶梯单元 */for(let i = 0; i < that.data.mid_item - 1; i++){that.data.opacity_list.push((80 - i * unit) / 100)}that.setData({opacity_list: that.data.opacity_list})//初始化遮盖层列表for(let i = 0; i < that.data.opacity_list.length; i++){let row = {opacity: that.data.opacity_list[i]}that.data.cover_list.push(row)}that.data.cover_list.push({ opacity: 0 })for(let i = 0; i < that.data.opacity_list.length; i++){let row = { opacity: that.data.opacity_list[that.data.opacity_list.length - 1 - i] }that.data.cover_list.push(row)}that.setData({cover_list: that.data.cover_list})//初始化选择器中每一项高度//初始化选项透明度，用于突出选中选项for(let i in that.data.list){let row = { top: 0, bottom: 0};// let topBase = (that.data.mid_item - 1) * that.data.picker.choose_item_height//顶端空白区域占用大小let topBase = 0row.top = topBase + i * that.data.picker.choose_item_heightif(i == that.data.list.length - 1){row.bottom = topBase + (parseInt(i) + 1) * that.data.picker.choose_item_height + 100}else{row.bottom = topBase + (parseInt(i) + 1) * that.data.picker.choose_item_height}that.data.item_height_list.push(row)that.setData({item_height_list: that.data.item_height_list})}},/*** 生命周期函数--监听页面加载*/onLoad: function (options) {let that = thisthat.init();},/*** 生命周期函数--监听页面初次渲染完成*/onReady: function () {},/*** 生命周期函数--监听页面显示*/onShow: function () {},/*** 生命周期函数--监听页面隐藏*/onHide: function () {},/*** 生命周期函数--监听页面卸载*/onUnload: function () {},/*** 页面相关事件处理函数--监听用户下拉动作*/onPullDownRefresh: function () {},/*** 页面上拉触底事件的处理函数*/onReachBottom: function () {},/*** 用户点击右上角分享*/onShareAppMessage: function () {}})
WXML:
<view class="box" style="height:{{box_height}}px;width:{{picker.box_width}}px;background:{{picker.bgColor}};"><scroll-view class="scroll_box" scroll-y="{{true}}" scroll-with-animation="{{picker.scroll_animation}}" bindscroll="bindscrollevent" scroll-into-view="{{scroll_into_view}}" scrollTop='{{scrollTop}}'><view wx:for="{{mid_item - 1}}" class="cushion" style="height:{{picker.choose_item_height}}px;line-height:{{picker.choose_item_height}}px;font-size:{{picker.choose_item_font_size}}px;color:{{picker.bgColor}}" id="cushion_top_{{index}}">·</view><view wx:for="{{list}}" class="choose_item" style="height:{{picker.choose_item_height}}px;line-height:{{picker.choose_item_height}}px;font-size:{{picker.choose_item_font_size}}px;color:{{picker.choose_item_font_color}}" id="item_{{index}}">{{item}}</view><view wx:for="{{mid_item - 1}}" class="cushion" style="height:{{picker.choose_item_height}}px;line-height:{{picker.choose_item_height}}px;font-size:{{picker.choose_item_font_size}}px;color:{{picker.bgColor}};" id="cushion_bottom_{{index}}">·</view></scroll-view><!-- 透明度遮盖 --><view style="position: fixed;top: 0;left: 70px;width:60px;z-index:9" bindtouchmove="touchMove" ><view wx:for='{{cover_list}}' style="height: {{picker.choose_item_height}}px;width: 100%;background: {{picker.bgColor}};opacity: {{item.opacity}}" ></view></view></view><view>{{picker_value}}</view>
wxss:
.box{}.scroll_box{height: 100%;width: 100%;}.choose_item{width: 100%;text-align: center;}.cushion{width: 100%;text-align: center;}.zhegai{height: 30px;width: 100%;position: absolute;top: 0;left: 0;background: #01356f;opacity: 0.9}
效果图
需要修改选择器直接修改data中picker内属性即可。选项逐渐变浅的效果比较让人头疼，最初的做法是对list内每个选项都加一个属性代表该选项的透明度，每次滑动都会修改显示的选项透明度，但是实际使用起来发现给选项赋值透明度的过程非常明显，导致体验不好。最后采用了现在这种方法，在文字上加了一排遮盖的view，这些view有不同的透明度从而展示出来渐变的效果，省去了每次滑动都要给选项修改透明度的烦恼。
