HTML5 原生 DragEnter/DragLeave 事件交替触发

Question

我在我的 Angular 应用程序中使用原生 HTML 拖放，发现此事件闪烁问题

This 回答不能解决我的问题，因为他们正在手动移动元素。我将其留在本机实现上。

我的简化代码：

var app = angular.module('app', []);
app.directive('amDnd', function() {
  return {
    scope: true,
    link: function($scope, $element, $attr) {
      var el = $element[0];
      el.draggable = true;

      el.addEventListener('dragenter', function dragEnter(e) {
        console.log($scope.$id, 'dragEnter');
      }, false);
      el.addEventListener('dragleave', function dragEnter(e) {
        console.log($scope.$id, 'dragleave');
      }, false);

    }
  };
});

div[am-dnd] {
  border: 2px solid red;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="app">
  <div am-dnd>
    <p>DRAG ME</p>
  </div>
  <div am-dnd>
    <h3>DRAG OVER THIS AREA</h3>
    <p>See the console, drag enter and leave are fired again and again while draging over
    </p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Animi quisquam, eaque, iure mollitia similique magnam voluptatem blanditiis distinctio nemo! Laboriosam porro iste maiores sequi magnam similique ad, in at. Omnis.</p>
  </div>

</div>

Answer 1

我感觉“闪烁”问题的根源在于第二个 am-dnd 指令的每个子元素都发生了 dragenter/dragleave 事件。有一个 Stack Overflow 问题讨论了对此 here 的修复。

您也许可以像这样声明 CSS 规则：

.child-elements {
   pointer-events: none;
}

...并在事件触发期间使用 jqLit​​e 将此类应用于 am-dnd 指令的所有子元素：

element.children().addClass("child-elements");

我做了一个JSFiddle，当第一个指令被拖到第二个指令上时，“闪烁”事件被最小化，但是第二个指令被拖到第一个指令上仍然存在一些问题。不过，我希望这能为您指明正确的方向。

var app = angular.module('app', []);
app.directive('amDnd', function () {
    return {
        scope: true,
        link: function (scope, element, attrs) {
            element.attr('draggable', 'true');

            element.on('dragenter', function () {
                element.children().addClass("child-elements");
                console.log('dragEnter');
            });
            element.on('dragleave', function () {
                element.children().removeClass("child-elements");
                console.log('dragleave');
            });
        }
    };
});

Answer 2

最适合我需要的解决方案：

var app = angular.module('app', []);
app.directive('amDnd', function() {
  return {
    scope: true,
    link: function($scope, $element, $attr) {
      var el = $element[0],
        counter = 0;
      el.draggable = true;

      el.addEventListener('dragenter', function dragEnter(e) {
        if (e.target === el && !counter) {
          console.log($scope.$id, 'dragEnter');
        }
        counter++;
      }, false);
      el.addEventListener('dragleave', function dragLeave(e) {
        counter--;
        if (e.target === el && !counter) {
          console.log($scope.$id, 'dragleave');
        }
      }, false);

    }
  };
});

div[am-dnd] {
  border: 2px solid red;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="app">
  <div am-dnd id='id1'>
    <p>DRAG ME</p>
  </div>
  <div am-dnd id='id2'>
    <h3>DRAG OVER THIS AREA</h3>
    <p>See the console, drag enter and leave are fired again and again while draging over
    </p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Animi quisquam, eaque, iure mollitia similique magnam voluptatem blanditiis distinctio nemo! Laboriosam porro iste maiores sequi magnam similique ad, in at. Omnis.</p>
  </div>

</div>