使用JavaScript在SortableJS可排序列表上模拟拖放

Question

我试图在使用可排序库创建的可排序HTML列表上模拟拖放操作。它使用本机HTML5API实现可拖动元素和列表中的排序。

为了模拟这些拖动事件，我找到并修改了以下JavaScript代码：

var triggerSortableDragAndDrop = function (selectorDrag, selectorDrop, callback) {
  var DELAY_INTERVAL_MS = 10;
  var MAX_TRIES = 2;

  // fetch target elements
  var elemDrag = document.querySelector(selectorDrag);
  var elemDrop = document.querySelector(selectorDrop);
  elemDrag.setAttribute('draggable',"true");
  elemDrop.setAttribute('draggable',"true");
  elemDrag.href="#";
  
  var dragItems = document.querySelectorAll('[draggable=true]');


  if (!elemDrag || !elemDrop) {
    console.log("can't get elements");
    return false;
  }

  var startingDropRect = elemDrop.getBoundingClientRect();

  function rectsEqual(r1, r2) {
    return r1.top === r2.top && r1.right === r2.right && r1.bottom === r2.bottom && r1.left === r2.left;
  }

  // function for triggering mouse events
  function fireMouseEvent(type, elem) {
    var evt = document.createEvent('MouseEvent');
    evt.initMouseEvent(type, true, true, window, 1, 1, 1, 0, 0, false, false, false, false, 0, elem);
    elem.dispatchEvent(evt);
  };

  // trigger dragging process on top of drop target
  // We sometimes need to do this multiple times due to the vagaries of
  // how Sortable manages the list re-arrangement
  var counter = 0;
  function dragover() {
    counter++;
    console.log('DRAGOVER #' + counter);

    var currentDropRect = elemDrop.getBoundingClientRect();
    if (rectsEqual(startingDropRect, currentDropRect) && counter < MAX_TRIES) {
      if (counter != 1) console.log("drop target rect hasn't changed, trying again");

      // mouseover / mouseout etc events not necessary
      // dragenter / dragleave events not necessary either
      fireMouseEvent('dragover', elemDrop);

      setTimeout(dragover, DELAY_INTERVAL_MS);
    } else {
      if (rectsEqual(startingDropRect, currentDropRect)) {
        console.log("wasn't able to budge drop target after " + MAX_TRIES + " tries, aborting");
        fireMouseEvent('drop', elemDrop);
        if (callback) callback(false);
      } else {
        setTimeout(drop, DELAY_INTERVAL_MS);
      }
    }
  }

  function drop() {
    console.log('DROP');
    // release dragged element on top of drop target
    fireMouseEvent('drop', elemDrop);
    fireMouseEvent('mouseup', elemDrop);    // not strictly necessary but I like the symmetry
    if (callback) callback(true);
  }

  // start dragging process
  console.log('DRAGSTART');
  fireMouseEvent('mousedown', elemDrag);
  console.log('mousedown triggered');
  fireMouseEvent('dragstart', elemDrag);
  console.log('dragstart triggered');

  // after a delay, do the first dragover; this will run up to MAX_TRIES times
  // (with a delay between each run) and finally run drop() with a delay:
  setTimeout(dragover, DELAY_INTERVAL_MS);
  return true;
};

我尝试拖放的部分的标记如下：

当我尝试在浏览器的拖动事件侦听器上设置断点，并在浏览器控制台中使用以下命令执行helper函数时：

triggerSortableDragAndDrop('#bookmarkItems > li:nth-child(2)', '#bookmarkItems > li:nth-child(2)');

我注意到dragstart事件从未被捕获，但mousedown和dragover事件被捕获。

如何让dragstart事件触发其侦听器？因为我认为这就是导致拖放模拟失败的原因。

Answer 1

我使用了一种更现代的方法来触发dragstart和mousedown事件（注意，使用事件构造函数比使用document.createEvent（）更可取）。这两项活动都按预期进行。下面是一些代码来说明这一点：

let text = document.getElementById('image');
text.addEventListener('dragstart', () => {
  console.log('dragstart triggered')
});
text.addEventListener('mousedown', () => {
  console.log('mousedown triggered')
});

function btn_click() {
  const evt_1 = new MouseEvent('mousedown');
 text.dispatchEvent(evt_1);
  
  const evt_2 = new DragEvent('dragstart');
 text.dispatchEvent(evt_2);
}

<p>Drag around the image to trigger the ondragstart and mousedown event.</p>
<button onclick='btn_click()'>Programatically trigger the ondragstart and onmousedown events.</button>
<br>
<br>
<img id='image' src='https://via.placeholder.com/150'>

Answer 2

我可以在您的代码中看到，Dragstart事件是由类型为MouseEvent的类型创建的，而它是类型为DragEvent的。

var elem = document.getElementById("one");
var mousedown = document.createEvent('MouseEvent');
mousedown.initMouseEvent("mousedown", true, true, window, 1, 1, 1, 0, 0, false, false, false, false, 0, elem);
elem.dispatchEvent(mousedown);
var dragstart = document.createEvent('DragEvent');
dragstart.initMouseEvent("dragstart", true, true, window, 1, 1, 1, 0, 0, false, false, false, false, 0, elem);
elem.dispatchEvent(dragstart);

<div id="one" draggable="true" onmousedown="console.log('mousedown')" ondragstart="console.log('dragstart')">drag me</div>