用jquery修复菜单。向下滚动时菜单不会出现？

Question

当我向下滚动时，我想让标题下方的导航栏导航显示在屏幕顶部！ 向下滚动时菜单不会立即显示。它在进一步向下滚动后出现！

还有人可以解释一下这个吗？ $（窗口）.height（） - 70;我无法弄清楚会回来的东西。

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

首先，没有理由添加display: none。使用fadeIn就足够了。其次，每个滚动都在执行该功能！这是不，不。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，但仅限于nav元素的状态更改。另外，我们可以display: none而不是display: block / 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，你应该测试scrolltop与头容器的高度，即160px。在第二个条件if中，我们需要在标题容器的高度上加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');
        }
    });

});

fiddle

Answer 2

菜单修复的歇斯底里版本：

$(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");
      }
    }
}); 

}）;