monitor op on scroll rect for behaviors like pull-down-reloading

ScrollRectHelper.cs

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

public class ScrollRectHelper : MonoBehaviour
{
	public ScrollRect scrollRect; 
	lua.LuaFunction eventDelegate;
	UnityEngine.Events.UnityAction<Vector2> onValueChanged;
	int movingCheckSize;

	void Awake()
	{
		onValueChanged = new UnityEngine.Events.UnityAction<Vector2>(OnValueChanged);
		scrollRect.onValueChanged.AddListener(onValueChanged);
	}


	public void Setup(lua.LuaFunction eventDelegate, int movingCheckSize = 100)
	{
		this.movingCheckSize = movingCheckSize;
		if (this.eventDelegate != null)
			this.eventDelegate.Dispose();
		if (eventDelegate != null)
			this.eventDelegate = eventDelegate.Retain();
		else
			this.eventDelegate = null;
    }

	Vector3[] temp1 = new Vector3[4];
	Bounds? viewportBounds;

	/*

        001|   010   | 100
       ----+---------+----
    001 000| 010 000 | 100 000 
       ----+---------+----
001 000 000|         | 100 000 000
           010 000 000
	*/
	const int bLeft = 1;
	const int bCenter = 2; 
	const int bRight = 4; 
	public int TestAgainstViewport(RectTransform rect)
	{
		if (!viewportBounds.HasValue)
		{
			var b = new Bounds();
			scrollRect.viewport.GetWorldCorners(temp1);
			b.Encapsulate(temp1[0]);
			b.Encapsulate(temp1[1]);
			b.Encapsulate(temp1[2]);
			b.Encapsulate(temp1[3]);
			viewportBounds = b;
		}
		rect.GetWorldCorners(temp1);
		var center = (temp1[0] + temp1[1] + temp1[2] + temp1[3]) / 4;
		var min = viewportBounds.Value.min;
		var max = viewportBounds.Value.max;
		int result = 0;
		if (center.x < min.x)
		{
			result = bLeft;
		}
		else if (center.x > max.x)
		{
			result = bRight;
		}
		else
		{
			result = bCenter;
		}
		if (center.y < min.y)
		{
			result = result << 6;
		}
		else if (center.y > max.y)
		{
			// nothing here
		}
		else
		{
			result = result << 3;
		}
		return result;
	}

	void OnDestroy()
	{
		if (eventDelegate != null)
			eventDelegate.Dispose();
		eventDelegate = null;
		scrollRect.onValueChanged.RemoveListener(onValueChanged);
	}
	
	public void MoveToHead()
	{
		if (scrollRect.vertical)
		{
			scrollRect.verticalNormalizedPosition = 1;
		}
		else if (scrollRect.horizontal)
		{
		}
	}


	Vector2? prevValue;
	Vector2? markedValue;
	void OnValueChanged(Vector2 value)
	{
		if (eventDelegate == null) return;

		if (scrollRect.vertical)
		{
			if (markedValue.HasValue)
			{
				var sizeY = scrollRect.content.sizeDelta.y;
				var curPos = sizeY * value.y;
				var markedPos = sizeY * markedValue.Value.y;
				if (Mathf.Abs(curPos - markedPos) > movingCheckSize)
				{
					if (value.y < prevValue.Value.y)
					{
						var height = scrollRect.content.sizeDelta.y * value.y;
						if (height < movingCheckSize)
						{
							eventDelegate.Invoke("touchEnd");
						}
					}
					else if (value.y > prevValue.Value.y)
					{
						var height = scrollRect.content.sizeDelta.y * (1 - value.y);
						if (height < movingCheckSize)
						{
							eventDelegate.Invoke("touchHead");
						}
					}

					if (value.y < prevValue.Value.y)
					{
						eventDelegate.Invoke("movingTowardsEnd");
					}
					else
					{
						eventDelegate.Invoke("movingTowardsHead");
					}
					markedValue = value;
				}
			}
			else
			{
				markedValue = value;
			}

			prevValue = value;

		}
		else if (scrollRect.horizontal)
		{
		}


	}

}