UGUI源代码分析（EventData）

EventData，事件数据，记录当前事件相关的信息。

有抽象基类AbstractEventData，衍生出的有BaseEventData，后者又有衍生类PointerEventData和AxisEventData。EventData是UI系统总事件的承载者，其中包含有与该事件相关的各种信息。
AbstractEventData只负责一件事，用于处理和获取该事件是否被使用的状态。
BaseEventData比上面多了两个属性，即当前的输入模块currentInputModule和当前选中的对象selectedObject
AxisEventData也就只包含一个字段，一个属性，分别是移动的方向和移动矢量
PointerEventData是最复杂的，它里面多了很多和点击，触发相关的信息，该类代码如下

using System;
using System.Text;
using System.Collections.Generic;

namespace UnityEngine.EventSystems
{
    /// <summary>
    /// Each touch event creates one of these containing all the relevant information.
    /// </summary>
    public class PointerEventData : BaseEventData
    {
        // 鼠标按钮的左中右键
        public enum InputButton
        {
            Left = 0,
            Right = 1,
            Middle = 2
        }
        // 某一帧内按键的状态
        public enum FramePressState
        {
            Pressed,
            Released,
            PressedAndReleased,
            NotChanged
        }

        public GameObject pointerEnter { get; set; }            // 接收OnPointerEnter事件的对象

        private GameObject m_PointerPress;
        public GameObject lastPress { get; private set; }       //上一次响应按下事件的对象
        public GameObject rawPointerPress { get; set; }         // 发生按下事件的对象，即使它不能响应该事件
        public GameObject pointerDrag { get; set; }             // 接收OnDrag事件的对象


        public RaycastResult pointerCurrentRaycast { get; set; }  // 当前事件关联的射线投射结果
        public RaycastResult pointerPressRaycast { get; set; }      // 按下（点击）事件关联的射线投射结果

        public List<GameObject> hovered = new List<GameObject>();  // 存储的是一组对象，这些对象都接收过OnPointerEnter事件

        public bool eligibleForClick { get; set; }                  // 当前事件是否用于点击

        public int pointerId { get; set; }

        public Vector2 position { get; set; }           // 当前点击（鼠标或触摸）位置
        public Vector2 delta { get; set; }              // 与上一帧点击的变化量
        public Vector2 pressPosition { get; set; }      // 按下的位置
        // World-space position where a ray cast into the screen hits something
        [Obsolete("Use either pointerCurrentRaycast.worldPosition or pointerPressRaycast.worldPosition")]
        public Vector3 worldPosition { get; set; }
        // World-space normal where a ray cast into the screen hits something
        [Obsolete("Use either pointerCurrentRaycast.worldNormal or pointerPressRaycast.worldNormal")]
        public Vector3 worldNormal { get; set; }
        public float clickTime { get; set; }                            // 上一次点击的时间
        public int clickCount { get; set; }                             // 点击的数量

        /* 和拖拽相关的信息 */
        public Vector2 scrollDelta { get; set; }                        // 与上一帧相比的滑动量
        public bool useDragThreshold { get; set; }                      // 是否使用拖拽阈值
        public bool dragging { get; set; }                              // 是否正在拖动

        public InputButton button { get; set; }

        public PointerEventData(EventSystem eventSystem) : base(eventSystem)
        {
            eligibleForClick = false;

            pointerId = -1;
            position = Vector2.zero; // Current position of the mouse or touch event
            delta = Vector2.zero; // Delta since last update
            pressPosition = Vector2.zero; // Delta since the event started being tracked
            clickTime = 0.0f; // The last time a click event was sent out (used for double-clicks)
            clickCount = 0; // Number of clicks in a row. 2 for a double-click for example.

            scrollDelta = Vector2.zero;
            useDragThreshold = true;
            dragging = false;
            button = InputButton.Left;
        }

        public bool IsPointerMoving()
        {
            return delta.sqrMagnitude > 0.0f;
        }

        public bool IsScrolling()
        {
            return scrollDelta.sqrMagnitude > 0.0f;
        }

        public Camera enterEventCamera
        {
            get { return pointerCurrentRaycast.module == null ? null : pointerCurrentRaycast.module.eventCamera; }
        }

        public Camera pressEventCamera
        {
            get { return pointerPressRaycast.module == null ? null : pointerPressRaycast.module.eventCamera; }
        }

        public GameObject pointerPress
        {
            get { return m_PointerPress; }
            set
            {
                if (m_PointerPress == value)
                    return;

                lastPress = m_PointerPress;
                m_PointerPress = value;
            }
        }

        public override string ToString()
        {
            var sb = new StringBuilder();
            sb.AppendLine("<b>Position</b>: " + position);
            sb.AppendLine("<b>delta</b>: " + delta);
            sb.AppendLine("<b>eligibleForClick</b>: " + eligibleForClick);
            sb.AppendLine("<b>pointerEnter</b>: " + pointerEnter);
            sb.AppendLine("<b>pointerPress</b>: " + pointerPress);
            sb.AppendLine("<b>lastPointerPress</b>: " + lastPress);
            sb.AppendLine("<b>pointerDrag</b>: " + pointerDrag);
            sb.AppendLine("<b>Use Drag Threshold</b>: " + useDragThreshold);
            sb.AppendLine("<b>Current Rayast:</b>");
            sb.AppendLine(pointerCurrentRaycast.ToString());
            sb.AppendLine("<b>Press Rayast:</b>");
            sb.AppendLine(pointerPressRaycast.ToString());
            return sb.ToString();
        }
    }
}

以上便是EventData 的大概内容吧，理解都在注释里了，本次水文结束