fix[DndList]: fixed drag bug (#1527)

https://github.com/PanJiaChen/vue-element-admin/issues/1524

src/components/DndList/index.vue

@@ -4,7 +4,7 @@
       <h3>{{ list1Title }}</h3>
       <draggable :list="list1" :options="{group:'article'}" class="dragArea">
         <div v-for="element in list1" :key="element.id" class="list-complete-item">
-          <div class="list-complete-item-handle">[{{ element.author }}] {{ element.title }}</div>
+          <div class="list-complete-item-handle">{{ element.id }}[{{ element.author }}] {{ element.title }}</div>
           <div style="position:absolute;right:0px;">
             <span style="float: right ;margin-top: -20px;margin-right:5px;" @click="deleteEle(element)">
               <i style="color:#ff4949" class="el-icon-delete"/>
@@ -15,9 +15,9 @@
     </div>
     <div :style="{width:width2}" class="dndList-list">
       <h3>{{ list2Title }}</h3>
-      <draggable :list="filterList2" :options="{group:'article'}" class="dragArea">
-        <div v-for="element in filterList2" :key="element.id" class="list-complete-item">
-          <div class="list-complete-item-handle2" @click="pushEle(element)"> [{{ element.author }}] {{ element.title }}</div>
+      <draggable :list="list2" :options="{group:'article'}" class="dragArea">
+        <div v-for="element in list2" :key="element.id" class="list-complete-item">
+          <div class="list-complete-item-handle2" @click="pushEle(element)">{{ element.id }} [{{ element.author }}] {{ element.title }}</div>
         </div>
       </draggable>
     </div>
@@ -60,16 +60,6 @@ export default {
       default: '48%'
     }
   },
-  computed: {
-    filterList2() {
-      return this.list2.filter(v => {
-        if (this.isNotInList1(v)) {
-          return v
-        }
-        return false
-      })
-    }
-  },
   methods: {
     isNotInList1(v) {
       return this.list1.every(k => v.id !== k.id)
@@ -90,9 +80,18 @@ export default {
       }
     },
     pushEle(ele) {
+      for (const item of this.list2) {
+        if (item.id === ele.id) {
+          const index = this.list2.indexOf(item)
+          this.list2.splice(index, 1)
+          break
+        }
+      }
+      if (this.isNotInList1(ele)) {
         this.list1.push(ele)
       }
     }
+  }
 }
 </script>