Add Ghost Element for Drag & Drop move

changelog/unreleased/enhancement-add-drag-drop-ghost

@@ -0,0 +1,7 @@
+Enhancement: Add Ghost Element for Drag & Drop
+
+We've added a custom ghost element for the drag&drop functionality in the OcTableFiles to
+better visualize the action to the user.
+
+https://github.com/owncloud/web/issues/5788
+https://github.com/owncloud/owncloud-design-system/pull/1754

src/components/molecules/OcTable/GhostElement/GhostElement.vue

@@ -0,0 +1,57 @@
+<template>
+  <div id="ghost-element" class="ghost-element">
+    <oc-icon :name="firstPreviewIcon" size="large" />
+    <span class="badge">{{ itemCount }}</span>
+  </div>
+</template>
+
+<script>
+/**
+ * Please head to the OcTableFiles component (https://owncloud.design/#/oC%20Components/OcTableFiles) for a demo of the Ghost Element.
+ */
+export default {
+  name: "GhostElement",
+  props: {
+    previewItems: {
+      type: Array,
+      required: true,
+    },
+  },
+  computed: {
+    firstPreviewIcon() {
+      const icon = this.previewItems[0].icon
+      return icon ? icon : "file"
+    },
+    itemCount() {
+      return this.previewItems.length
+    },
+  },
+}
+</script>
+
+<style lang="scss">
+.ghost-element {
+  background-color: transparent;
+  padding-top: 4px;
+  padding-left: 5px;
+  z-index: var(--oc-z-index-modal);
+  position: absolute;
+  .badge {
+    position: absolute;
+    top: -2px;
+    right: -8px;
+    padding: 4px;
+    line-height: 10px;
+    -webkit-border-radius: 30px;
+    -moz-border-radius: 30px;
+    border-radius: 30px;
+    min-width: 10px;
+    height: 10px;
+    text-align: center;
+
+    font-size: 12px;
+    background: red;
+    color: white;
+  }
+}
+</style>

src/components/molecules/OcTable/OcTable.vue

@@ -46,12 +46,12 @@
           $emit(constants.EVENT_TROW_CONTEXTMENU, $refs[`row-${trIndex}`][0], $event, item)
         "
         @hook:mounted="$emit(constants.EVENT_TROW_MOUNTED, item, $refs[`row-${trIndex}`][0])"
-        @dragstart.native="dragStart(item)"
+        @dragstart.native="dragStart(item, $event)"
         @drop.native="dropRowEvent(item.id, $event)"
         @dragenter.native.prevent="dropRowStyling(item.id, false, $event)"
         @dragleave.native.prevent="dropRowStyling(item.id, true, $event)"
         @mouseleave="dropRowStyling(item.id, true, $event)"
-        @dragover.native.prevent
+        @dragover.native="dragOver($event)"
       >
         <oc-td
           v-for="(field, tdIndex) in fields"
@@ -79,6 +79,7 @@
   </table>
 </template>
 <script>
+import Vue from "vue"
 import OcThead from "../../atoms/_OcTableHeader/_OcTableHeader.vue"
 import OcTbody from "../../atoms/_OcTableBody/_OcTableBody.vue"
 import OcTr from "../../atoms/_OcTableRow/_OcTableRow"
@@ -87,6 +88,7 @@ import OcTd from "../../atoms/_OcTableCellData/_OcTableCellData.vue"
 import OcButton from "../../atoms/OcButton/OcButton.vue"
 import SortMixin from "../../../mixins/sort"
 import { getSizeClass } from "../../../utils/sizeClasses"
+import GhostElement from "./GhostElement/GhostElement.vue"
 
 import {
   EVENT_THEAD_CLICKED,
@@ -214,6 +216,11 @@ export default {
       required: false,
       default: false,
     },
+    selection: {
+      type: Array,
+      required: false,
+      default: () => [],
+    },
   },
   data() {
     return {
@@ -248,8 +255,34 @@ export default {
     },
   },
   methods: {
-    dragStart(file) {
+    dragOver(event) {
+      event.preventDefault()
+    },
+    setGhostElement(file, event) {
+      const selection = [...this.selection]
+      selection.splice(
+        selection.findIndex(function (i) {
+          return i.id === file.id
+        }),
+        1
+      )
+      const GhostElementComponent = Vue.extend(GhostElement)
+      const ghostInstances = new GhostElementComponent({
+        propsData: {
+          previewItems: [file, ...selection],
+        },
+      })
+      ghostInstances.$mount()
+      const ghost = document.body.appendChild(ghostInstances.$el)
+      ghost.style.left = "-99999px"
+      ghost.style.top = "-99999px"
+      event.dataTransfer.setDragImage(ghost, 0, 0)
+      event.dataTransfer.dropEffect = "move"
+      event.dataTransfer.effectAllowed = "move"
+    },
+    dragStart(file, event) {
       if (!this.dragDrop) return
+      this.setGhostElement(file, event)
       this.$emit(EVENT_FILE_DRAGGED, file)
     },
     dropRowEvent(id, event) {

src/components/templates/OcTableFiles/OcTableFiles.vue

@@ -8,6 +8,7 @@
     :header-position="headerPosition"
     :drag-drop="dragDrop"
     :hover="hover"
+    :selection="selection"
     @highlight="fileClicked"
     @rowMounted="rowMounted"
     @contextmenuClicked="showContextMenu"