Unity3d拖动标题栏移动对话框（面板）

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

//通过拖动标题栏移动对话框（面板）
public class DragDialogByTitleBar : MonoBehaviour, IPointerDownHandler, IDragHandler{
	
    //鼠标按下位置
	private Vector2 _ptStartMousePoint;

    //对话框（面板）初始位置
    private Vector3 _ptStartDialogPoint;

    //对话框（面板）
    private RectTransform _dlgRt;

    //对话框（面板）父实体
    private RectTransform _dlgParentRt;
	
	void Awake () {
		_dlgRt = transform.parent as RectTransform;
		_dlgParentRt = _dlgRt.parent as RectTransform;
	}
	
    //按下鼠标
	public void OnPointerDown (PointerEventData data) {
		_ptStartDialogPoint = _dlgRt.localPosition;
		RectTransformUtility.ScreenPointToLocalPointInRectangle (_dlgParentRt, data.position, data.pressEventCamera, out _ptStartMousePoint);
	}
	
    //拖拽
	public void OnDrag (PointerEventData data) {
		if (_dlgRt == null || _dlgParentRt == null)
			return;
		
		Vector2 localPointerPosition;
		if (RectTransformUtility.ScreenPointToLocalPointInRectangle (_dlgParentRt, data.position, data.pressEventCamera, out localPointerPosition)) {
			Vector3 offsetToOriginal = localPointerPosition - _ptStartMousePoint;
			_dlgRt.localPosition = _ptStartDialogPoint + offsetToOriginal;
		}
		
		ClampToWindow ();
	}
	
	//将窗口限定在屏幕内
	void ClampToWindow () {
		Vector3 pos = _dlgRt.localPosition;
		
		Vector3 minPosition = _dlgParentRt.rect.min - _dlgRt.rect.min;
		Vector3 maxPosition = _dlgParentRt.rect.max - _dlgRt.rect.max;
		
		pos.x = Mathf.Clamp (_dlgRt.localPosition.x, minPosition.x, maxPosition.x);
		pos.y = Mathf.Clamp (_dlgRt.localPosition.y, minPosition.y, maxPosition.y);
		
		_dlgRt.localPosition = pos;
	}
}