Snap

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

public class Snap : MonoBehaviour, IBeginDragHandler, IEndDragHandler, IDragHandler {

    public RectTransform sr;
    public List<RectTransform> transforms = new List<RectTransform>();
    public float snapOffset = 20f;
    public float lerpSpeed = 20f;

    private RectTransform snappingTransform;
    private bool canSnap;

    private void Start() {
        if(GetComponent<ScrollRect>())
            GetComponent<ScrollRect>().inertia = false;
        else
            Debug.LogWarning("Coloca no scroll rect");
    }

    private void Update() {
        if(!snappingTransform)
            snappingTransform = transforms.FirstOrDefault();

        if(canSnap)
            sr.position = Vector3.Lerp(sr.position, snappingTransform.position, lerpSpeed * Time.deltaTime);
    }

    public void OnBeginDrag(PointerEventData eventData) {
        canSnap = false;
    }

    public void OnEndDrag(PointerEventData eventData) {
        var offset = eventData.delta.x;

        if(Mathf.Abs(offset) > snapOffset) {
            var currentIndex = transforms.IndexOf(snappingTransform);
            currentIndex += (int)Mathf.Sign(offset);
            currentIndex = Mathf.Clamp(currentIndex, 0, transforms.Count - 1);
            snappingTransform = transforms[currentIndex];
        }

        canSnap = true;
    }

    public void OnDrag(PointerEventData eventData) {
        var distances = new float[transforms.Count];

        for(int i = 0; i < distances.Length; i++)
            distances[i] = Vector2.Distance(transforms[i].position, sr.position);

        var nearestDistance = Mathf.Min(distances);

        snappingTransform = (from rect in transforms
                             where Mathf.Approximately(Vector2.Distance(rect.position, sr.position), nearestDistance)
                             select rect).FirstOrDefault();
    }
}