PointerEventData.dragging

描述

确定用户在拖动鼠标还是在触控板上滑动。

如果用户在移动鼠标或触控板指针，则 PointerEventData.dragging 返回 /true/。如果鼠标或触控板指针未移动，则返回 /false/。dragging 利用鼠标或触控板手指的移动。OnDrag 包含 dragging 事件。

以下示例使用 IDragHandler、IDragHandler 和 IEndDragHandler 接口。这些接口分别提供 EventTrigger.OnBeginDrag、EventTrigger.OnDrag 和 EventTrigger.OnEndDrag 事件处理程序。当指针开始移动时，IDragHandler.OnDrag 进行查询，仅当用户拖动指针时才会发送消息。

using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;

// PointerEventDrag.dragging example.

// PointerEventData.dragging is set to true when the object is moving.
// Otherwise dragging is set to false.
//
// Create a 2D Project and add a Canvas and an Image as a child. Position the Image in the center
// of the Canvas. Resize the Image to approximately a quarter of the height and width. Create a
// Resources folder and add a sprite. Set the sprite to the Image component. Then add this script
// to the Image. Then press the Play button. The Image should be clickable and moved with the
// mouse or trackpad.

public class Example : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
    private Vector3 position;
    private float timeCount = 0.0f;

    public void OnBeginDrag(PointerEventData eventData)
    {
        position = transform.position;
        Debug.Log("OnBeginDrag: " + position);
    }

    // Drag the selected item.
    public void OnDrag(PointerEventData data)
    {
        if (data.dragging)
        {
            // Object is being dragged.
            timeCount += Time.deltaTime;
            if (timeCount > 0.25f)
            {
                Debug.Log("Dragging:" + data.position);
                timeCount = 0.0f;
            }
        }
        transform.position = data.position;
    }

    public void OnEndDrag(PointerEventData eventData)
    {
        transform.position = position;
        Debug.Log("OnEndDrag: " + position);
    }
}