判断是鼠标拖拽还是点击

using UnityEngine;
using System.Collections;
using Deduction;
public class MouseInput : MonoBehaviour {

public static MouseInput instance;

void Awake()
{
instance = this;
}

//鼠标左键事件
public event mousePosHandler leftDownEvent;
public event mousePosHandler leftUpEvent;
public event mousePosHandler leftDragEvent;
public event mousePosHandler leftDragDeltaEvent;
public event mousePosHandler leftRelaxedEvent;
public event mousePosHandler leftClickEvent;

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Vector2 posLeftDown;//记录鼠标左键按下的位置
Vector2 posLeftPre;
bool isLeftPressed = false;
bool clickEnable = true;

//鼠标滚轮事件
public event mouseScrollHandler mouseScrollEvent;

//鼠标中键事件
public event mousePosHandler middleDownEvent;
public event mousePosHandler middleUpEvent;
public event mousePosHandler middleDragEvent;
public event mousePosHandler middleDragDeltaEvent;
public event mousePosHandler middleRelaxedEvent;

Vector2 posMiddlePre;
bool isMiddlePressed = false;

void Update()
{
//鼠标左键
if (Input.GetMouseButtonDown(0))
{
isLeftPressed=true;
clickEnable = true;
posLeftDown = Input.mousePosition;
posLeftPre = Input.mousePosition;
if(leftDownEvent!=null)
leftDownEvent(Input.mousePosition);
}

if (isLeftPressed)
{
if(((Vector2)Input.mousePosition-posLeftDown).sqrMagnitude>9)
{
clickEnable = false;
}
if (!clickEnable)
{
if (leftDragEvent != null)
leftDragEvent(Input.mousePosition);
Vector2 leftDragDelta = (Vector2)Input.mousePosition -posLeftPre;
posLeftPre = Input.mousePosition;
if (leftDragDeltaEvent != null)
leftDragDeltaEvent(leftDragDelta);
}
}
else
{
if (leftRelaxedEvent!=null)
{
leftRelaxedEvent(Input.mousePosition);
}
}

if (Input.GetMouseButtonUp(0))
{
isLeftPressed = false;
if (leftUpEvent != null)
leftUpEvent(Input.mousePosition);
if(clickEnable)
{
if (leftClickEvent != null)
leftClickEvent(Input.mousePosition);
}
}

//鼠标中键
if (Input.GetMouseButtonDown(2))
{
isMiddlePressed = true;
posMiddlePre = Input.mousePosition;
if (middleDownEvent != null)
middleDownEvent(Input.mousePosition);
}

if (isMiddlePressed)
{
if (middleDragEvent != null)
middleDragEvent(Input.mousePosition);
Vector2  middleDragDelta = (Vector2)Input.mousePosition - posMiddlePre;
posMiddlePre = Input.mousePosition;
if (middleDragDeltaEvent != null)
middleDragDeltaEvent(middleDragDelta);
}
else
{
if (middleRelaxedEvent != null)
middleRelaxedEvent(Input.mousePosition);
}

if (Input.GetMouseButtonUp(2))
{
isMiddlePressed = false;
if (middleUpEvent != null)
middleUpEvent(Input.mousePosition);
}

//鼠标滚轮
float scroll = Input.GetAxis("Mouse ScrollWheel");
if (!Mathf.Approximately(scroll,0))
{
if (mouseScrollEvent != null)
mouseScrollEvent(scroll);
}
}
}