使用 jquery 修复顶部的菜单。向下滚动时以后不会出现菜单？

Question

我想让标题下方的导航栏导航在向下滚动时出现在屏幕顶部！ 向下滚动时，菜单不会立即出现。进一步向下滚动后出现！

还有人可以解释一下吗？ $(窗口).height() - 70;我不知道它会返回什么。

jquery 代码：

$(document).ready(function(){
    $(".nav").slideDown(800);

    $(window).on('scroll',function(){
        var navHeight = $(window).height() - 70;
        if ( $(window).scrollTop()> navHeight){
            $('.nav').addClass('fixed');
            $('.nav').css("display","none");
            $('.nav').fadeIn("fast");
        }
        else{
            $('.nav').removeClass('fixed');
            $('.nav').css("display","block");
        }
    });

});

我的html代码：

<div id="header">
    <div id="header-container">
        Logo goes here!!
    </div>
</div>

<div class="nav">
    <div class="nav-container">
        <ul>
            <li><a href="#">Home</a></li>
            <li><a href="#">Portfolio</a></li>
            <li><a href="#">Browse</a></li>
            <li><a href="#">Contact</a></li>
            <li><a href="#">About</a></li>
        </ul>
    </div>
</div>


<div class="main-body">
    <div class="article-area">
        <div class="article">
            <h3>This is the title</h3>
            <hr>
            <img src="imgtest.jpg"></img>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
            </p><p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
            </p><p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
            <div class="clear"></div>
        </div>

        <div class="article">
            <h3>This is the title</h3>
            <hr>
            <img src="imgtest.jpg"></img>
            <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
            </p><p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
            </p><p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum
            <div class="clear"></div>
        </div>          
    </div>

    <div class="sidebar-area">
        ertertre
    </div>
    <div class="clear"></div>
</div>

我的css代码：

body{
    margin: 0;
    padding: 0;
    background: #cccccc;
}

.clear {
    clear: both;
}

#header{
    background: #FF9900;
    height: 160px;
    width: 100%;
}

#header-container{
    width: 960px;
    height: 160px;
    margin: 0px auto 0px auto;
}

.nav{
    width: 100%;
    height: 70px;
    background: rgba(0,0,0,0.5);
    display:none; /*hiding it for cool jquery slide down effect*/
}

.fixed {
    position: fixed; 
    top: 0; 
    height: 70px; 
    z-index: 1;
}

.nav .nav-container{
    width: 960px;
    height: 62px;
    margin: 0 auto;
}

.nav .nav-container ul{
    padding-top: 6px;
    margin: 0 auto;
}

.nav .nav-container ul li{
    display: inline;
    padding: 0px;
    border-radius: 10px;
    margin-right: 20px;
    margin-left: 7px;
    background: #000000;
}

.nav .nav-container ul li a{
    color: #FF9900;
    text-decoration: none;
    font-weight: bold;
    font-size: 22px;
    display: inline-block;
    width:150px;
    text-align: center;
    height: 58px;
    line-height: 250%;
    background: black;
    border-radius: 10px;

}

.nav .nav-container ul li a:hover{
    background:#FF9900;
    color: white;
    border-radius: 10px; 
}

.main-body{
    width: 960px;
    background: white;
    margin:0 auto;
    min-height: 700px;
}

.article-area{
    width: 600px;
    min-height: 700px;
    float: left;
    margin: 20px;
    margin-bottom: 0px;
}

.sidebar-area{
    width: 280px;
    min-height: 400px;
    background: green;
    float: right;
    margin: 20px;
}

.article{
    padding: 10px;
    border: 1px solid white;
    background: #FAFAF8;
    box-shadow: 0.5px 0.5px 4px black;
    margin-bottom: 20px;
    border-radius: 5px;
}

.article p{
    width: 550px;
}

.article img{
    float: right;
    overflow: auto;
    margin-left: 10px;
}

.article h3{
    padding: 10px;
    font-size: 26px;
    padding: 3px;
    margin:0px;
}

.upper-footer{
    width: 100%;
    height: 250px;
    background: black;
}

Answer 1

一个歇斯底里版本的菜单修复：

$(document).ready(function(){
$(".nav").slideDown(800);

// glueMenu use for hysteresis, jittery in transition.
// also, want outside callback for persistance.
var gluedMenu = false;

$(window).on('scroll',function(){

    // glue on when scroll past header container plus your fixed position in CSS
    var navHeight1 = $('.header-container').height() + 70;

    // unglue when scroll past returns back 10 pixels after fixed position
    var navHeight2 = $('.header-container').height() + 60;

    if ( $(window).scrollTop()> navHeight1 ) {
      if (gluedMenu == false) {
        gluedMenu = true;
        $('.nav').addClass('fixed');
        $('.nav').css("display","none");
        $('.nav').fadeIn("fast");
      }
    }
    else if ( $(window).scrollTop() < navHeight2 ) {
      if (gluedMenu == true) {
        gluedMenu = false;
        $('.nav').removeClass('fixed');
        $('.nav').css("display","block");
      }
    }
}); 

});

Answer 2

首先没有理由添加display: none。使用 fadeIn 就足够了。其次，每次滚动您都在执行该功能！这是不行的。相反，我们可以添加一些额外的逻辑来确保我们不会无休止地执行回调，但前提是 nav 元素的状态发生变化。另外，不用display: none/display: block，我们可以只使用fadeOut(0).fadeIn('fast')，因为动画队列在jquery中是同步的。最后，您错误地得到 window.height() 并从中减去任意值 70。相反，您应该测试滚动顶部与标题容器的高度，即 160 像素。在第二个条件if中，我们需要将header容器的高度加1，以确保在向上滚动时移除固定类。

$(document).ready(function(){
    $(".nav").slideDown(800);

    $(window).on('scroll',function(){
        //var navHeight = $(window).height() - 70;
        if ( $(window).scrollTop() > $('.header-container').height() && $('.nav:not(.fixed)').length ){
            $('.nav').addClass('fixed').fadeOut(0).fadeIn('fast');
        }
        else if( $(window).scrollTop() < $('.header-container') + 1 && $('.nav.fixed').length ){
            $('.nav').removeClass('fixed').fadeOut(0).fadeIn('fast');
        }
    });

});

fiddle