Tips and best practices for drag-and-drop selection and placement in Vue

Vue is a popular JavaScript framework suitable for building single page applications (SPA). It supports drag-and-drop selection and placement functions through instructions and components, providing users with a better interactive experience. This article will introduce the techniques and best practices for drag-and-drop selection and placement in Vue.

1. Drag and drop command

Vue provides a v-draggable command that can easily achieve dragging effects. This command can be applied to any element, and can customize the drag style, limit the drag range, etc.

The following is a simple example:

<template>
  <div v-draggable>
    拖拽我
  </div>
</template>
<script>
  import draggable from 'vuedraggable'
  export default {
    directives: {
      draggable
    }
  }
</script>

In the above example, we imported the directive provided by the vuedraggable library and declared the directive in the Vue component. Elements using v-draggable can be dragged by the user.

2. Selecting and Unchecking

In drag and drop operations, you usually need to click to select an element before you can drag it. The following is a sample code to implement selection and deselection:

<template>
  <div v-for="(item, index) in items"
       :key="index"
       :class="{selected: index === selectedIndex}"
       @mousedown="onSelect(index)"
       @mouseup="onDeselect"
       v-draggable>
      {{ item }}
  </div>
</template>
<script>
  import draggable from 'vuedraggable'
  export default {
    directives: {
      draggable
    },
    data () {
      return {
        items: ['Item 1', 'Item 2', 'Item 3'],
        selectedIndex: null
      }
    },
    methods: {
      onSelect (index) {
        this.selectedIndex = index
      },
      onDeselect () {
        this.selectedIndex = null
      }
    }
  }
</script>

In the above example, we use a v-for loop to render the list and store the index of the element currently selected by the user through the selectedIndex variable. When the element is clicked, the onSelect method will be called to update the selectedIndex variable; when the mouse is raised, the selectedIndex will be updated to be empty, indicating that the user has canceled the selection operation.

3. Drag restrictions

In drag operations, sometimes it is necessary to limit the range and direction of drag. Vue provides several ways to implement this restriction.

3.1. Limit the range

By passing an object containing the start and end coordinates in v-draggable, you can limit the drag range. The following is an example code:

<template>
  <div v-for="(item, index) in items"
       :key="index"
       :class="{selected: index === selectedIndex}"
       @mousedown="onSelect(index)"
       @mouseup="onDeselect"
       v-draggable="{startX: 0, startY: 0, endX: 100, endY: 100}">
      {{ item }}
  </div>
</template>

In the above example, we limit the dragging range to the upper left corner (0, 0) to the lower right corner (100, 100). The user cannot drag elements outside this range. .

3.2. Limit the direction

By passing in the axis attribute in v-draggable, you can limit the dragging direction of the element. The following is the example code:

<template>
  <div v-for="(item, index) in items"
       :key="index"
       :class="{selected: index === selectedIndex}"
       @mousedown="onSelect(index)"
       @mouseup="onDeselect"
       v-draggable="{axis: 'x'}">
      {{ item }}
  </div>
</template>

In the above example, we set axis to 'x', which means that the element can only be dragged along the horizontal direction.

4. Place operation

After dragging is completed, it is usually necessary to place the element at the specified location. Vue provides a v-droppable directive that can be used to implement drop operations.

The following is a simple implementation process:

<template>
  <div>
    <div v-for="(item, index) in items"
         :key="index"
         :class="{selected: index === selectedIndex}"
         @mousedown="onSelect(index)"
         @mouseup="onDeselect"
         v-draggable>
        {{ item }}
    </div>
    <div v-droppable @drop="onDrop">
      放置目标
    </div>
  </div>
</template>
<script>
  export default {
    data () {
      return {
        items: ['Item 1', 'Item 2', 'Item 3'],
        selectedIndex: null
      }
    },
    methods: {
      onSelect (index) {
        this.selectedIndex = index
      },
      onDeselect () {
        this.selectedIndex = null
      },
      onDrop (evt) {
        const droppedItem = this.items[this.selectedIndex]
        this.$set(this.items, this.selectedIndex, null)
        this.$set(this.items, evt.target.dataset.index, droppedItem)
        this.selectedIndex = null
      }
    }
  }
</script>

In the above example, we use the v-droppable directive to set a div element as the drop target. When the user drags the dragged element When placed on the div element, the drop event will be triggered. We implement the placement operation of the element in the onDrop method.

Although the above code can implement the placement operation of elements, it still has some shortcomings. For example, we cannot know the position of the target element from the dragged element. At this time, we can use some supplementary interfaces of drag and drop events to solve this problem.

5. Best Practices

Implementing a smooth drag-and-drop operation requires comprehensive consideration of many aspects, so we should try our best to meet the following best practices in practice:

• Use native events and drag-and-drop event interfaces as much as possible instead of implementing custom drag-and-drop logic.
• Restrict the drag-and-drop operation of elements, such as limiting the range and direction, to ensure user experience.
• When performing placement operations, you need to consider a variety of factors, such as whether there are other elements blocking it.
• While implementing drag-and-drop operations, it is necessary to ensure the scalability and maintainability of the code.

In short, through the flexible use of instructions and drag-and-drop event interfaces, we can not only achieve smooth drag-and-drop operations, but also improve the user experience and bring better interactive effects to the application.

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