使用 jquery 修复顶部的菜单。向下滚动时菜单不显示？

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，菜单不会立即显示。进一步向下滚动后出现！

还有人可以解释一下吗？ $（窗口）.高度（） - 70;我无法弄清楚它会返回什么。

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;
}

菜单

修复的滞后版本：

$(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");
      }
    }
});

}）;

首先，没有理由添加display: none。使用淡入就足够了。其次，每次滚动时，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。同样不用使用 display: none/display: block ，我们可以fadeOut(0).fadeIn('fast')因为动画队列在 jquery 中是同步的。最后，您错误地获取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 160px。在第二个条件 if 中，我们需要在标头容器的高度上加 1，以确保在向上滚动时删除固定类。

$(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');
        }
    });
});

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