滚动触发的动画极度延迟 [英] scroll triggered animation extremely delayed

问题描述

我使用jQuery，尝试制作类似于

Using jQuery, I am trying to make a navbar similar to this Wordpress plugin: The navbar is hidden/offscreen when the page is loaded, slides down to a fixed position when a certain scroll position is reached, and slides back up to its offscreen position when the user scrolls back up to the top.

我设法做到了，但是，时机完全不对:滚动后可能要花费几秒钟，直到出现菜单栏.向上滚动时会更糟:起初我以为它根本不起作用，但是然后，有时经过15秒甚至更长的时间，它最终又向上移动了.

I managed to do it, however, the timing is completely wrong: It can take a few seconds after scrolling until the menu bar appears. And it's worse when scrolling up: At first I thought that it doesn't work at all, but then, after sometimes 15 seconds or even more, it eventually moves back up.

这是我的代码:

$(window).scroll(function() {
  var scrollposition = $(window).scrollTop();
  if (scrollposition > 100) {
    $("#main_navigation").animate({
      top: "0px"
    }, 600);
  };
  if (scrollposition < 100) {
    $("#main_navigation").animate({
      top: "-82px"
    }, 400);
  };
});

html,
body {
  margin: 0;
  height: 100%;
}
.content {
  height: 200%;
  background: #fda;
  padding: 5em 3em;
}

nav#main_navigation {
  position: fixed;
  z-index: 1;
  top: -82px;
  width: 100%;
  background: #fff;
  height: 54px;
  border-bottom: 1px solid #eee;
}

.logo {
  display: inline-block;
  position: relative;
  top: 50%;
  left: 2em;
  margin: 0;
  width: 36px;
  transform: translateY(-50%);
}

nav#main_navigation ul {
  position: relative;
  top: 50%;
  margin: 0;
  transform: translateY(-50%);
  display: inline-block;
  list-style: none;
  float: right;
  margin-right: 0.8em;
}

nav#main_navigation li {
  display: inline-block;
  margin-right: 1.2em;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<nav id="main_navigation">
  <div class="logo">(logo)</div>
  <ul>
    <li><a href="#">Welcome</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Contact</a></li>
  </ul>
</nav>
<div class="content">
  <p>This is the content. Scroll down at least 100px to make the navbar appear. This should take 0.6 seconds, but takes much longer.</p>
  <p>Then scroll back up to make the navbar disappear again. This should only take 0.4 seconds...</p>
</div>

我想这可能与必须处理太多滚动事件有关，但是我不知道如何避免或过滤该事件.还是还有其他原因?

I suppose it might have to do with too many scroll events having to be handled, but I don't know how to avoid or filter that. Or is there another reason?

推荐答案

我发现:有很多滚动事件，并且每个滚动事件都会触发一个动画，这显然是对于浏览器来说太多了.在处理完所有这些动画并最终执行动画之前，要花很长时间，这会导致较长的延迟.

I figured it out: There are a lot of scroll events, and there is an animation triggered with each scroll event, which obviously is too much to handle for the browser. It takes a very long time until all those are processed and the animation is eventually performed, causing the long delay.

因此，我寻找了一种方法，使上下滑动的动画仅在触发另一个动画之前被触发一次.我使用了一个变量(status_1)，其默认值为"closed".当滚动值超过100时，仅当status_1被关闭"时才触发第一个(向下滑动)动画.但是status_1一旦被触发，就会被设置为打开"，因此只要滚动值大于100，就不会再次被触发.与第二个if条件和动画相同:

So I looked for a way to have the down- and up-sliding animations only be triggered once before the other one is triggered. I used a variable (status_1), whose default value is "closed". When the scroll value goes above 100, the first (down-sliding) animation is triggered only if status_1 is "closed". But as soon as it's triggered, status_1 is set to "open", so it won't be triggered again as long as the scroll value is above 100. Same with the second if-condition and animation:

var status_1 = "closed";
$(window).scroll(function() {
  var scrollposition = $(this).scrollTop();
  if ((scrollposition > 100) && (status_1 == "closed")) {
    $('#main_navigation').animate({
      top: '0px'
    }, 600);
    status_1 = "open";
  };
  if ((scrollposition < 100) && (status_1 == "open")) {
    $('#main_navigation').animate({
      top: '-82px'
    }, 400);
    status_1 = "closed";
  };
});

html,
body {
  margin: 0;
  height: 100%;
}

.content {
  height: 200%;
  background: #fda;
  padding: 5em 3em;
}

nav#main_navigation {
  position: fixed;
  z-index: 1;
  top: -82px;
  width: 100%;
  background: #fff;
  height: 54px;
  border-bottom: 1px solid #eee;
}

.logo {
  display: inline-block;
  position: relative;
  top: 50%;
  left: 2em;
  margin: 0;
  width: 36px;
  transform: translateY(-50%);
}

nav#main_navigation ul {
  position: relative;
  top: 50%;
  margin: 0;
  transform: translateY(-50%);
  display: inline-block;
  list-style: none;
  float: right;
  margin-right: 0.8em;
}

nav#main_navigation li {
  display: inline-block;
  margin-right: 1.2em;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<nav id="main_navigation">
  <div class="logo">(logo)</div>
  <ul>
    <li><a href="#">Welcome</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Contact</a></li>
  </ul>
</nav>
<div class="content">
  <p>This is the content. Scroll down at least 100px to make the navbar appear. This should take 0.6 seconds.</p>
  <p>Then scroll back up to make the navbar disappear again. This should only take 0.4 seconds...</p>
</div>

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