scrollbar problem in my chat window, its freezing, here's my video of its behaviour

Unity Engine
1

video link- My Screencast

Code-

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class APITest : MonoBehaviour 
{
	public Vector2 scrollPosition = Vector2.zero;
    private string message = "";
    private Vector2 scrollView = Vector2.zero;
	 public Rect MainRect = new Rect(40, 20, 350, 125);

    private void Start()
    {
        TextChat.messages = new ArrayList();
    }

    private void OnGUI()
    {
		
		MainRect = GUI.Window(0, MainRect, DoMainWindow, "Shout Box");
		
//        GUILayout.BeginArea(new Rect(0, 30, Screen.width, Screen.height - 60));
//        scrollView = GUILayout.BeginScrollView(scrollView);
//        foreach(string c in TextChat.messages)
//        {
//            GUILayout.Label(c);
//        }
//        GUILayout.EndArea();
//        GUILayout.EndScrollView();
//        scrollView.y++;	
//        message = GUI.TextField(new Rect(0, Screen.height - 30, Screen.width - 50, 25), message);
//        if (GUI.Button(new Rect(Screen.width - 50, Screen.height - 30, 50, 25), "Send"))
//        {
//            TextChat.cleaning = TextChat.Clean.none;
//            GameObject.Find("Chat").GetComponent<TextChat>().sendMessage(message);
//            message = "";
//        }
    }
	
	void DoMainWindow(int windowID)
   {
		int y = 20;
		Rect scrollRect = new Rect(10,10, MainRect.width - 30, MainRect.height - 60);
		int height = TextChat.messages.Count * 20;
		scrollPosition = GUI.BeginScrollView(scrollRect, scrollPosition, new Rect(0, 0, 0, height+20));
		string output;
		foreach(string c in TextChat.messages)
        {
			
           // GUILayout.Label(c);
			output = c;
			GUI.Button(new Rect(5, y, MainRect.height - 30, MainRect.width - 50),output, "label");
			y+=20;
			//Debug.Log (height+"="+TextChat.messages.Count+"*"+"20");
			//scrollView.y++;
			
        }
		
		GUI.EndScrollView ();
		//scrollPosition = new Vector2(0,height);
		
		
		message = GUI.TextField(new Rect(5, MainRect.height - 30, MainRect.width - 50, 25), message);
      if (GUI.Button(new Rect(MainRect.width - 45, MainRect.height - 30, 45, 25), "Send"))
        {
            TextChat.cleaning = TextChat.Clean.none;
            GameObject.Find("Chat").GetComponent<TextChat>().sendMessage(message);
            message = "";
        }
		GUI.DragWindow();
	}
}
2

It’s not moving because the script keeps putting back at the bottom of the window. Try making the position only update when the send button is pressed. Hope this helps!