How can I restrict/constrain my drag and drop of sprites to only be on the screen?

I am trying to keep the sprites I drag and drop to be only in the screen. I don´t want it to be possible to drag and drop outside of the screen view. Is it a good way to solve this so I can change the screen size without any problems later?

This is my code so far :

		void OnMouseDown ()
		{

				screenPoint = Camera.main.WorldToScreenPoint (gameObject.transform.position);

		}

		void OnMouseDrag ()
		{
						Vector3 currentScreenPoint = new Vector3 (Input.mousePosition.x, 60, screenPoint.z);
						Vector3 currentPos = Camera.main.ScreenToWorldPoint (currentScreenPoint);
						transform.position = currentPos;


		}

This is to use a drag and drop constraint to the X axis to make my own slider. Now, I need it to stop where the screen ends on both sides of the X axis.

I solved it with using a Mathf.Clamp. First I got confused with Mathf.Clamp because of the documentation mentions Time.time etc.
But after watching Will Goldstones tutorial on it I figured it out : http://www.youtube.com/watch?v=ZggxVn93ePI

Here is my C# code for it :

		void Update(){

		transform.position =  new Vector3(Mathf.Clamp(transform.position.x, -5.0f, 5.0f),0,0);

		}

Thanks man … you saved my time … you are king