Unity UGUI实现简单拖拽图片功能

using UnityEngine;
using UnityEngine.EventSystems;
using System.Collections;
using System;

//给空间添加监听事件要实现的一些接口
public class MyDrag : MonoBehaviour, IPointerDownHandler, IDragHandler, IPointerUpHandler, 
 IEndDragHandler, IPointerEnterHandler, IPointerExitHandler {

 public RectTransform canvas;   //得到canvas的ugui坐标
 private RectTransform imgRect;  //得到图片的ugui坐标
 Vector2 offset = new Vector3(); //用来得到鼠标和图片的差值
 Vector3 imgReduceScale = new Vector3(0.8f, 0.8f, 1); //设置图片缩放
 Vector3 imgNormalScale = new Vector3(1, 1, 1); //正常大小

 // Use this for initialization
 void Start () {
  imgRect = GetComponent<RectTransform>();

 }

 //当鼠标按下时调用 接口对应 IPointerDownHandler
 public void OnPointerDown(PointerEventData eventData)
 {
  Vector2 mouseDown = eventData.position; //记录鼠标按下时的屏幕坐标
  Vector2 mouseUguiPos = new Vector2(); //定义一个接收返回的ugui坐标
  //RectTransformUtility.ScreenPointToLocalPointInRectangle()：把屏幕坐标转化成ugui坐标
  //canvas：坐标要转换到哪一个物体上，这里img父类是Canvas，我们就用Canvas
  //eventData.enterEventCamera：这个事件是由哪个摄像机执行的
  //out mouseUguiPos：返回转换后的ugui坐标
  //isRect：方法返回一个bool值，判断鼠标按下的点是否在要转换的物体上
  bool isRect = RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas, mouseDown, eventData.enterEventCamera, out mouseUguiPos);
  if (isRect) //如果在
  {
   //计算图片中心和鼠标点的差值
   offset = imgRect.anchoredPosition - mouseUguiPos;
  }
 }

 //当鼠标拖动时调用 对应接口 IDragHandler
 public void OnDrag(PointerEventData eventData)
 {
  Vector2 mouseDrag = eventData.position; //当鼠标拖动时的屏幕坐标
  Vector2 uguiPos = new Vector2(); //用来接收转换后的拖动坐标
  //和上面类似
  bool isRect = RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas, mouseDrag, eventData.enterEventCamera, out uguiPos);

  if (isRect)
  {
   //设置图片的ugui坐标与鼠标的ugui坐标保持不变
   imgRect.anchoredPosition = offset + uguiPos;
  }
 }

 //当鼠标抬起时调用 对应接口 IPointerUpHandler
 public void OnPointerUp(PointerEventData eventData)
 {
  offset = Vector2.zero;
 }

 //当鼠标结束拖动时调用 对应接口 IEndDragHandler
 public void OnEndDrag(PointerEventData eventData)
 {
  offset = Vector2.zero;
 }

 //当鼠标进入图片时调用 对应接口 IPointerEnterHandler
 public void OnPointerEnter(PointerEventData eventData)
 {
  imgRect.localScale = imgReduceScale; //缩小图片
 }

 //当鼠标退出图片时调用 对应接口 IPointerExitHandler
 public void OnPointerExit(PointerEventData eventData)
 {
  imgRect.localScale = imgNormalScale; //回复图片
 }
}