JavaScript 应用程序：尝试使 "wheel" 事件侦听器不连续失败

Question

我正在 Bootstrap 4 和 JavaScript 中开发一个小型 "Picture browser" 应用程序。

如下所示，有一个 "Prev" 和一个 "Next" 按钮可以帮助浏览图片。

我一直在努力寻找一种可靠的方法来使 鼠标滚动 的功能与这些按钮相同。向下滚动相当于单击 "Next" 按钮。向上滚动相当于单击 "Prev" 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，但过渡太...连续。我希望它与按钮触发的转换相同。

我错过了什么？

Answer 1

这里有几种解决方法：

-- 防止scroll滚动多张图片，可以使用这个函数：

// 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

-- 您应该更改函数的参数 updateCounter 以便它采用滚动图像的方向。（示例：布尔值：true = 下一个，false = 上一个）

--要恢复滚动的方向，参考这个答案：

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>

JavaScript 应用程序：尝试使 "wheel" 事件侦听器不连续失败

JavaScript application: trying to make the "wheel" event listener discontinuous fails

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