Top navbar (under header) fixed on top of screen w

问题:

When scrollbar is on top browser displays:

HTML:

-------------------------
|   HEADER              |
-------------------------
|   NAVBAR              |
-------------------------
|   body                |
-------------------------

When scrollbar is down NOW browser normally displays:

HTML:

-------------------------
|                       |
|   body                |
|                       |
-------------------------

But I'd like to have:

-------------------------
|   NAVBAR              |
-------------------------
|                       |
|   body                |
|                       |
-------------------------

I tried with:

<div id="navbar">...</div>

CSS:

#navbar {
  position:fixed;
  z-index:1;
}

But this only works if navbar is on the top position. I have the header on top...

回答1:

DEMO

I have used an image at top instead of the "HEADER" mentioned in your question.

This is the js I have used to make the header(navbar in your case) fixed.

var stickyNavTop = $('#header').offset().top;

$(window).scroll(function() {  
    if ($(window).scrollTop() > stickyNavTop) {
        $('#header').addClass('fixed');
    }
    else {
        $('#header').removeClass('fixed');
    }  
});

回答2:

A potential solution or class of solutions is called an Affix.

See boostrap's example here:

http://getbootstrap.com/javascript/#affix

The general strategy is to watch how close something is to the top of the window, and THEN make its CSS position: fixed like you tried to do.

This can be trickier than expected to implement on your own when it comes to 'unsticking' the element, as you need to track where it came from originally.

回答3:

Here's an example taken from html5rocks which works nice.

<style>
.sticky {
  position: fixed;
  top: 0;
}
.header {
  width: 100%;
  background: #F6D565;
  padding: 25px 0;
}
</style>

<div class="header"></div>

<script>
var header = document.querySelector('.header');
var origOffsetY = header.offsetTop;

function onScroll(e) {
  window.scrollY >= origOffsetY ? header.classList.add('sticky') :
                                  header.classList.remove('sticky');
}

document.addEventListener('scroll', onScroll);
</script>

For further reading: http://updates.html5rocks.com/2012/08/Stick-your-landings-position-sticky-lands-in-WebKit

Of course, .header here is your NAVBAR.

回答4:

You will tell #navbar where it should be fixed. Use the css properties top, left, bottom, right. In your case you only need laft top right set to 0 and a fixed height, for example 30px.