Bootstrap滚动监听组件scrollspy.js使用方法详解

其实滚动监听使用的情况还是很多的，比如导航居于右侧，当主题内容滚动某一块的时候，右侧导航对应的要高亮。

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实现功能

1、当滚动区域内设置的hashkey距离顶点到有效位置时，就关联设置其导航上的指定项
2、导航必须是 .nav > li > a 结构，并且a上href或data-target要绑定hashkey
3、菜单上必须有.nav样式
4、滚动区域的data-target与导航父级Id（一定是父级）要一致。

 
 
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下面来看一下实现的具体代码，原理：当滚动容器内的hashkey位置距离容器顶部只有 offset设置的值，就会设置导航中对应的href高亮。

ScrollSpy构造函数

首先新建一个构造函数，如下：

function ScrollSpy(element, options) {
  this.$body     = $(document.body)
  this.$scrollElement = $(element).is(document.body) ? $(window) : $(element)
  this.options    = $.extend({}, ScrollSpy.DEFAULTS, options)
  this.selector    = (this.options.target || '') + ' .nav li > a'
  this.offsets    = []
  this.targets    = []
  this.activeTarget  = null
  this.scrollHeight  = 0
  this.$scrollElement.on('scroll.bs.scrollspy', $.proxy(this.process, this))
  this.refresh()
  this.process()
 }

该构造函数主要干了啥：

1.基本设置，主要是设置当前滚动元素是设置的body还是具体的某一块元素；其次是导航的结构要是.nav li > a的结构，也就是你的菜单中也要有.nav这个class。

2.监听元素滚动的时候，执行process方法。

3.同时初始化的时候也执行了refresh与process方法。

下面讲解一下这几个方法。

getScrolHeight方法

获取滚动容器的内容高度（包含被隐藏部分）

this.$scrollElement[0].scrollHeight || Math.max(this.$body[0].scrollHeight, document.documentElement.scrollHeight)

refresh方法

刷新并存储滚动容器内各hashkey的值

ScrollSpy.prototype.refresh = function () {
  var that     = this
  var offsetMethod = 'offset'
  var offsetBase  = 0

  this.offsets   = []
  this.targets   = []
  this.scrollHeight = this.getScrollHeight()

  if (!$.isWindow(this.$scrollElement[0])) {
   offsetMethod = 'position'
   offsetBase  = this.$scrollElement.scrollTop()
  }

  this.$body
   .find(this.selector)
   .map(function () {
    var $el  = $(this)
    var href = $el.data('target') || $el.attr('href')
    var $href = /^#./.test(href) && $(href)
    
    return ($href
     && $href.length
     && $href.is(':visible')
     && [[$href[offsetMethod]().top + offsetBase, href]]) || null
   })
   .sort(function (a, b) { return a[0] - b[0] })
   .each(function () {
    that.offsets.push(this[0])
    that.targets.push(this[1])
   })

 }

它主要实现了什么呢？

1.默认用offset来获取定位值，如果滚动区域不是window则用position来获取

if (!$.isWindow(this.$scrollElement[0])) {
   offsetMethod = 'position'
   offsetBase  = this.$scrollElement.scrollTop()
  }

2.根据导航上的hashkey来遍历获取滚动区域内的hashkey对应的offset值：

this.$body
   .find(this.selector)
   .map(function () {
    var $el  = $(this)
    var href = $el.data('target') || $el.attr('href')
    var $href = /^#./.test(href) && $(href)
    
    return ($href
     && $href.length
     && $href.is(':visible')
     && [[$href[offsetMethod]().top + offsetBase, href]]) || null
   })
   .sort(function (a, b) { return a[0] - b[0] })
   .each(function () {
    that.offsets.push(this[0])
    that.targets.push(this[1])
   })

process方法

滚动条事件触发函数，用于计算当前需要高亮那个导航菜单

ScrollSpy.prototype.process = function () {
  var scrollTop  = this.$scrollElement.scrollTop() + this.options.offset
  var scrollHeight = this.getScrollHeight()
  var maxScroll  = this.options.offset + scrollHeight - this.$scrollElement.height()
  var offsets   = this.offsets
  var targets   = this.targets
  var activeTarget = this.activeTarget
  var i

  if (this.scrollHeight != scrollHeight) {
   this.refresh()
  }

  if (scrollTop >= maxScroll) {
   return activeTarget != (i = targets[targets.length - 1]) && this.activate(i)
  }

  if (activeTarget && scrollTop < offsets[0]) {
   this.activeTarget = null
   return this.clear()
  }

  for (i = offsets.length; i--;) {
   activeTarget != targets[i]
    && scrollTop >= offsets[i]
    && (offsets[i + 1] === undefined || scrollTop < offsets[i + 1])
    && this.activate(targets[i])
  }
 }

主要作用：

1.获取滚动容器已滚动距离：

var scrollTop  = this.$scrollElement.scrollTop() + this.options.offset

2.滚动容器可以滚动的最大高度:

var maxScroll  = this.options.offset + scrollHeight - this.$scrollElement.height()

3.设置滚动元素逻辑，给当前匹配元素添加高亮：

for (i = offsets.length; i--;) {
   activeTarget != targets[i]
    && scrollTop >= offsets[i]
    && (offsets[i + 1] === undefined || scrollTop < offsets[i + 1])
    && this.activate(targets[i])
  }

active方法

设置指定的导航菜单高亮

ScrollSpy.prototype.activate = function (target) {
  this.activeTarget = target

  this.clear()

  var selector = this.selector +
   '[data-target="' + target + '"],' +
   this.selector + '[href="' + target + '" rel="external nofollow" rel="external nofollow" ]'

  var active = $(selector)
   .parents('li')
   .addClass('active')

  if (active.parent('.dropdown-menu').length) {
   active = active
    .closest('li.dropdown')
    .addClass('active')
  }

  active.trigger('activate.bs.scrollspy')
 }

clear方法

清除所有高亮菜单

ScrollSpy.prototype.clear = function () {
  $(this.selector)
   .parentsUntil(this.options.target, '.active')
   .removeClass('active')
 }

源码

+function ($) {
 'use strict';

 // SCROLLSPY CLASS DEFINITION
 // ==========================

 function ScrollSpy(element, options) {
  this.$body     = $(document.body)
  this.$scrollElement = $(element).is(document.body) ? $(window) : $(element)
  this.options    = $.extend({}, ScrollSpy.DEFAULTS, options)
  this.selector    = (this.options.target || '') + ' .nav li > a'
  this.offsets    = []
  this.targets    = []
  this.activeTarget  = null
  this.scrollHeight  = 0
  this.$scrollElement.on('scroll.bs.scrollspy', $.proxy(this.process, this))
  this.refresh()
  this.process()
 }

 ScrollSpy.VERSION = '3.3.7'

 ScrollSpy.DEFAULTS = {
  offset: 10
 }

 ScrollSpy.prototype.getScrollHeight = function () {
  return this.$scrollElement[0].scrollHeight || Math.max(this.$body[0].scrollHeight, document.documentElement.scrollHeight)
 }

 ScrollSpy.prototype.refresh = function () {
  var that     = this
  var offsetMethod = 'offset'
  var offsetBase  = 0

  this.offsets   = []
  this.targets   = []
  this.scrollHeight = this.getScrollHeight()

  if (!$.isWindow(this.$scrollElement[0])) {
   offsetMethod = 'position'
   offsetBase  = this.$scrollElement.scrollTop()
  }

  this.$body
   .find(this.selector)
   .map(function () {
    var $el  = $(this)
    var href = $el.data('target') || $el.attr('href')
    var $href = /^#./.test(href) && $(href)
    
    return ($href
     && $href.length
     && $href.is(':visible')
     && [[$href[offsetMethod]().top + offsetBase, href]]) || null
   })
   .sort(function (a, b) { return a[0] - b[0] })
   .each(function () {
    that.offsets.push(this[0])
    that.targets.push(this[1])
   })

 }

 ScrollSpy.prototype.process = function () {
  var scrollTop  = this.$scrollElement.scrollTop() + this.options.offset
  var scrollHeight = this.getScrollHeight()
  var maxScroll  = this.options.offset + scrollHeight - this.$scrollElement.height()
  var offsets   = this.offsets
  var targets   = this.targets
  var activeTarget = this.activeTarget
  var i

  if (this.scrollHeight != scrollHeight) {
   this.refresh()
  }

  if (scrollTop >= maxScroll) {
   return activeTarget != (i = targets[targets.length - 1]) && this.activate(i)
  }

  if (activeTarget && scrollTop < offsets[0]) {
   this.activeTarget = null
   return this.clear()
  }

  for (i = offsets.length; i--;) {
   activeTarget != targets[i]
    && scrollTop >= offsets[i]
    && (offsets[i + 1] === undefined || scrollTop < offsets[i + 1])
    && this.activate(targets[i])
  }
 }

 ScrollSpy.prototype.activate = function (target) {
  this.activeTarget = target

  this.clear()

  var selector = this.selector +
   '[data-target="' + target + '"],' +
   this.selector + '[href="' + target + '" rel="external nofollow" rel="external nofollow" ]'

  var active = $(selector)
   .parents('li')
   .addClass('active')

  if (active.parent('.dropdown-menu').length) {
   active = active
    .closest('li.dropdown')
    .addClass('active')
  }

  active.trigger('activate.bs.scrollspy')
 }

 ScrollSpy.prototype.clear = function () {
  $(this.selector)
   .parentsUntil(this.options.target, '.active')
   .removeClass('active')
 }


 // SCROLLSPY PLUGIN DEFINITION
 // ===========================

 function Plugin(option) {
  return this.each(function () {
   var $this  = $(this)
   var data  = $this.data('bs.scrollspy')
   var options = typeof option == 'object' && option

   if (!data) $this.data('bs.scrollspy', (data = new ScrollSpy(this, options)))
   if (typeof option == 'string') data[option]()
  })
 }

 var old = $.fn.scrollspy

 $.fn.scrollspy       = Plugin
 $.fn.scrollspy.Constructor = ScrollSpy


 // SCROLLSPY NO CONFLICT
 // =====================

 $.fn.scrollspy.noConflict = function () {
  $.fn.scrollspy = old
  return this
 }


 // SCROLLSPY DATA-API
 // ==================

 $(window).on('load.bs.scrollspy.data-api', function () {
  $('[data-spy="scroll"]').each(function () {
   var $spy = $(this)
   Plugin.call($spy, $spy.data())
  })
 })

}(jQuery);

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持创新互联。

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