当用户滚动页面并在底部有一个箭头时,我想在屏幕上从页面顶部到底部画一条线。我不想使用固定位置以便它始终位于同一位置,我希望它通过确定页面长度等来指示它们在页面上的位置。
我有以下代码在一定程度上起作用。这个问题是当我滚动到一半时箭头从页面底部消失。
我尝试了此代码的不同变体,但都没有用。谁能帮忙?
//Draw dotted line on scroll - works to certain extent but scrolls off page
$( window ).scroll(function() {
if ( $.windowScrollTop() > 10 ) {
var pos = $.windowScrollTop();
var scrollHeight = $(window).innerHeight();
var element = $('#dashes');
$( '#line' ).css( 'height', pos - scrollHeight / 4 );
$( '#arrow' ).css( 'top', pos - scrollHeight / 4 );
} else {
$( '#line' ).css( 'height', '6px' );
$( '#arrow' ).css( 'top', '-150px' );
}
});
//also tried the below
$(window).on("scroll", function() {
var scrollHeight = $(document).height();
var scrollPosition = $(window).height() + $(window).scrollTop();
if ((scrollHeight - scrollPosition) / scrollHeight === 0) {
// when scroll to bottom of the page
alert('bottom');
} else {
$( '#line' ).css( 'height', $(window).scrollTop() );
$( '#arrow' ).css( 'top', $(window).scrollTop() );
}
});
最佳答案
我们在这里试图做的是将文档高度反射(reflect)到窗口高度的一个元素中。所以实际的可滚动文档高度将是
var actualScrollHeight = $(document).height() - $(window).height();
/* This is the distance we actually scroll */
我们的#line
的最大可能高度为
var lineMaxHeight = $(window).height() - topMargin - bottomMargin - arrowHeight;
/* #arrow is inside #line but we positioned it outside it's height */
没有在#line
元素高度反射(reflect)滚动进度我们需要做的是
var lineHeight = $(document).scrollTop() / actualScrollHeight * lineMaxHeight;
/* Super Easy, isn't it? */
最终结果:
您不需要同时定位 #line
和 #arrow
。修复 #line
底部的 #arrow
,然后只需更改 #line
的高度就可以了。我添加了 topMargin
和 bottomMargin
功能,使屏幕调整更具个性化。
$(function(){
var topMargin = 15, bottomMargin = 5;
var arrowHeight = $('#arrow').height();
var $lineElement = $('#line');
$lineElement.height(topMargin);
$(window).scroll(function() {
var winHeight = $(window).height();
var actualScrollHeight = $(document).height() - winHeight;
var lineMaxHeight = winHeight - topMargin - bottomMargin - arrowHeight;
var scrollTop = $(document).scrollTop();
var lineHeight = scrollTop / actualScrollHeight * lineMaxHeight;
$lineElement.height(topMargin + lineHeight);
});
});
#logo {
width: 80px;
background-color: #53befd;
padding: 20px;
}
#line {
background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAYAAAAMCAYAAABBV8wuAAAAFklEQVR42mNgoB74OEXzPzY8sBLUAwB6PmBV1D+CIAAAAABJRU5ErkJggg==);
position: fixed;
top: 0px;
right: 19px;
z-index: 20;
width: 3px;
}
#arrow {
background-color: #f28323;
height: 40px;
width: 40px;
position: absolute;
bottom: -40px;
left: -18px;
border-radius: 20px;
color: white;
text-align: center;
font-size: 32px;
line-height: 35px;
padding-top: 3px;
cursor: pointer;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="logo">LOGO </div>
<p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p><p> Page content go here<br /> and here<br /> and here<br /> and here<br /> and here</p>
<div id="line"><div id="arrow">V</div></div>
关于javascript - 计算图像的位置以跟随滚动条,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/49009234/