JavaScript 应用程序：尝试使"wheel"事件侦听器不连续失败

Question

我正在用Bootstrap 4和JavaScript开发一个小型的"图片浏览器"应用程序。

如下所示，有一个"上一个"和一个"下一个"按钮可以帮助浏览图片。

我一直在努力找到一种可靠的方法来使鼠标滚动功能与这些按钮相同。向下滚动相当于单击"下一步"按钮。向上滚动相当于单击"上一个"按钮。

var picArr = $('#pictures_list li');
// The index of the last element of the array is "maxIndex"
var maxIndex = picArr.length - 1;
// Initialize counter
var counter = 0;
var updateCounter = function(btn) {
var direction = $(btn).data("direction")
if (direction === "left") {
if (counter > 0) {
counter--;
} else {
counter = maxIndex;
}
} else {
if (counter < maxIndex) {
counter++;
} else {
counter = 0;
}
}
}
var showCount = function(container_id) {
var pageCount = counter + 1;
document.getElementById(container_id).innerHTML = "Picture " + pageCount + " of " + picArr.length;
}
var showSlide = function() {
var mTop = (200 * counter) * (-1) + 'px';
$('#pictures_list').animate({
'marginTop': mTop
}, 400);
}
showCount('show_count');
$('#controls button').on('click', function() {
updateCounter(this);
showSlide();
showCount('show_count');
});
document.getElementById("picture_frame").addEventListener("wheel", function() {
updateCounter(this);
showSlide();
showCount('show_count')
});

#picture_frame {
width: 200px;
height: 200px;
margin: 5px auto;
border: 1px solid #ccc;
border-radius: 2px;
overflow: hidden;
}
.controls>div {
display: inline-block;
}
#picture_frame {
height: 200px;
overflow: hidden;
}
#pictures_list {
flex-flow: row wrap;
align-items: stretch;
width: 200px;
}
#pictures_list li {
display: flex;
height: 200px;
flex: 1 100%;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="container">
<div id="picture_frame">
<ul id="pictures_list" class="list-unstyled d-flex">
<li><img src="https://picsum.photos/200/200
" alt="First picture"></li>
<li><img src="https://picsum.photos/200/200?gravity=east
" alt="Second picture"></li>
<li><img src="https://picsum.photos/200/200?gravity=west
" alt="Third picture"></li>
<li><img src="https://picsum.photos/200/200?gravity=north
" alt="Fourth picture"></li>
</ul>
</div>
<div class="text-center mb-2">
<span class="badge badge-primary" id="show_count"></span>
</div>
<div class="controls text-center">
<div class="btn-group" id="controls">
<button type="button" class="btn btn-primary btn-sm" data-direction="left">Prev</button>
<button type="button" class="btn btn-primary btn-sm" data-direction="right">Next</button>
</div>
</div>
</div>

在鼠标滚轮上触发showSlide()功能确实有效，但过渡也是......连续的。我希望它与按钮触发的过渡相同。

我错过了什么？

Answer 1

以下是几种解决方案：

-- 要防止滚动滚动多个图像，您可以使用此功能：

// Returns a function, that, as long as it continues to be invoked, will not
// be triggered. The function will be called after it stops being called for
// N milliseconds. If `immediate` is passed, trigger the function on the
// leading edge, instead of the trailing.
function debounce(func, wait, immediate) {
var timeout;
return function() {
var context = this, args = arguments;
var later = function() {
timeout = null;
if (!immediate) func.apply(context, args);
};
var callNow = immediate && !timeout;
clearTimeout(timeout);
timeout = setTimeout(later, wait);
if (callNow) func.apply(context, args);
};
};

见 https://davidwalsh.name/javascript-debounce-function

-- 您应该更改函数updateCounter的参数，使其采用滚动图像的方向。(示例：布尔值：真 = 下一个，假 = 上一个(

--要恢复卷轴的方向，请参考这个答案：https://stackoverflow.com/a/45719399/4864628

var picArr = $('#pictures_list li');
// The index of the last element of the array is "maxIndex"
var maxIndex = picArr.length - 1;
// Initialize counter
var counter = 0;
var updateCounter = function(direction) {
if (direction) {
if (counter > 0) {
counter--;
} else {
counter = maxIndex;
}
} else {
if (counter < maxIndex) {
counter++;
} else {
counter = 0;
}
}
}
var showCount = function(container_id) {
var pageCount = counter + 1;
document.getElementById(container_id).innerHTML = "Picture " + pageCount + " of " + picArr.length;
}
var showSlide = function() {
var mTop = (200 * counter) * (-1) + 'px';
$('#pictures_list').animate({
'marginTop': mTop
}, 400);
}
// Returns a function, that, as long as it continues to be invoked, will not
// be triggered. The function will be called after it stops being called for
// N milliseconds. If `immediate` is passed, trigger the function on the
// leading edge, instead of the trailing.
function debounce(func, wait, immediate) {
	var timeout;
	return function() {
		var context = this, args = arguments;
		var later = function() {
			timeout = null;
			if (!immediate) func.apply(context, args);
		};
		var callNow = immediate && !timeout;
		clearTimeout(timeout);
		timeout = setTimeout(later, wait);
		if (callNow) func.apply(context, args);
	};
};

showCount('show_count');
$('#controls button').on('click', function() {
updateCounter($(this).attr('data-direction') == 'left');
showSlide();
showCount('show_count');
});
var pictureFrame = document.getElementById("picture_frame");
var onScroll = debounce(function(direction) {
updateCounter(direction);
showSlide();
showCount('show_count')
}, 100, true);
pictureFrame.addEventListener("wheel", function(e) {
e.preventDefault();
var delta;
if (event.wheelDelta){
delta = event.wheelDelta;
}else{
delta = -1 * event.deltaY;
}

onScroll(delta >= 0);
});

#picture_frame {
width: 200px;
height: 200px;
margin: 5px auto;
border: 1px solid #ccc;
border-radius: 2px;
overflow: hidden;
}
.controls>div {
display: inline-block;
}
#picture_frame {
height: 200px;
overflow: hidden;
}
#pictures_list {
flex-flow: row wrap;
align-items: stretch;
width: 200px;
}
#pictures_list li {
display: flex;
height: 200px;
flex: 1 100%;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="container">
<div id="picture_frame">
<ul id="pictures_list" class="list-unstyled d-flex">
<li><img src="https://picsum.photos/200/200
" alt="First picture"></li>
<li><img src="https://picsum.photos/200/200?gravity=east
" alt="Second picture"></li>
<li><img src="https://picsum.photos/200/200?gravity=west
" alt="Third picture"></li>
<li><img src="https://picsum.photos/200/200?gravity=north
" alt="Fourth picture"></li>
</ul>
</div>
<div class="text-center mb-2">
<span class="badge badge-primary" id="show_count"></span>
</div>
<div class="controls text-center">
<div class="btn-group" id="controls">
<button type="button" class="btn btn-primary btn-sm" data-direction="left">Prev</button>
<button type="button" class="btn btn-primary btn-sm" data-direction="right">Next</button>
</div>
</div>
</div>