滚动下来时，有没有办法在我的网站上创建一个div？

Question

I'm trying to replicate this: http://twitter.github.com/bootstrap/base-css.html#typography (the one on top that has the tabs: | Typography | Code Tables | Forms | Buttons | Icons by Glyphicons |). I'd like to replicate that same fast acting effect.

I'd like to make this div do the same:

#panel {
    margin: auto;
    border-bottom: 1px solid rgba(0,0,0,.6);
    border-top: 0;
    box-shadow: 0 1px rgba(0,0,0,.1),
    1px 0 rgba(0,0,0,.1),
    -1px 0 rgba(0,0,0,.1),
    0 -1px rgb(255,255,255) inset,
    0 1px 2px rgba(0,0,0,.2) inset,
    1px 0 rgb(255,255,255) inset,
    -1px 0 rgb(255,255,255) inset;
    background: #E8E8E8;    
    width: 75%;
    -webkit-border-bottom-left-radius: 5px;
    -moz-border-radius-bottomleft: 5px;
    -moz-border-radius-bottomright: 5px;
    -webkit-border-bottom-right-radius: 5px;
    color: rgba(0,0,0,.7);
    text-shadow: 0 1px white;
    padding: 2px 0px 2px 8px;
    margin-top: -149px;
    text-align: left;
    font-size: 11px;
}

on my website: http://www.bobbaxtrade.com

Thanks :)

Answer 1

I've created the jsFiddle here: http://jsfiddle.net/cBk7q/

So, you need to add a class to your css rules, to make your div static on top of the window:

.fixed {
    position: fixed;
    top: 0;
    left: 0;
}

Then, add a jQuery function to bind the scroll event and add the fixed class when you reach the desired position:

<script type="text/javascript">
    var $mydiv = $("#mydiv"),
        origTop = $("#mydiv").position().top;

    $(window).scroll(function(e) {
        if( document.body.scrollTop > origTop) {
            console.log($mydiv.hasClass('fixed'));
            $mydiv.addClass("fixed");
        }
        else {
            console.log('c ' + (document.body.scrollTop > origTop));
            $mydiv.removeClass("fixed");
        }
    });
</script>

Answer 2

The Bootstrap website explains you how to use this feature .

If you are using bootstrap, you can use the CSS class navbar-fixed-top to get this behavior:

<div id="panel" class="navbar navbar-fixed-top">
  ...
</div>

If you want the effect, that the navigation bar only becomes fixed after scrolling over it, you need to add the class navbar-fixed-top dynamically with some JavaScript (taken from LessCSS ).

Suppose you have some HTML

<!-- some content -->
<div id ="panel">
  …
</div>
<!-- enough other content to make the document scroll -->

and some CSS

.navbar-fixed-top {
  position: fixed;
  top: 0;
  left: 0;
}

Then the following JS will give you the requested behavior.

var docked = false;
var menu = document.getElementById('panel');
var init = menu.offsetTop;

function scrollTop() {
  return document.body.scrollTop || document.documentElement.scrollTop;
}

window.onscroll = function () {
  if (!docked && (menu.offsetTop - scrollTop() < 0)) {
    menu.style.top = 0;
    menu.className = 'navbar-fixed-top';
    docked = true;
  } else if (docked && scrollTop() <= init) {
    menu.style.top = init + 'px';
    menu.className = menu.className.replace('navbar-fixed-top', '');
    docked = false;
  }
};

This example works in Firefox, Chrome, Opera and Safari. Internet Explorer needs a workaround.

Answer 3

If you're using jQuery, try https://github.com/bigspotteddog/ScrollToFixed . Basic usage would be:

$(document).ready(function() {
    $('#panel').scrollToFixed();
});

... however, see the link for options (eg allowing for footer panels when the user scrolls down, etc).