Unity3d iphone手指拖拽

using UnityEngine;
using System.Collections;

public class Test : MonoBehaviour {
private Vector3 screenPoint;
private Vector3 offset;
// Update is called once per frame
void Update () {
for (int i = 0; i < Input.touchCount; ++i) {
if (Input.GetTouch(i).phase == TouchPhase.Began) {
screenPoint = Camera.main.WorldToScreenPoint(gameObject.transform.position);

offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.GetTouch(i).position.x, Input.GetTouch(i).position.y, screenPoint.z));
}
if(Input.GetTouch(i).phase == TouchPhase.Moved) {
Vector3 curScreenPoint = new Vector3(Input.GetTouch(i).position.x, Input.GetTouch(i).position.y, screenPoint.z);

Vector3 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint) + offset;
transform.position = curPosition;
}
}
}

}