UNITY UI Scroll through items one by one

7 years later we still need this.

 

This work for vetical snapping: Be caution that you need to adjust the distance and distReposition value for you own project

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5. using UnityEngine.UI;
6.  
7. public class ScrollRectSnap : MonoBehaviour
8. {
9.     public RectTransform panel;
10.     public Button[] bttn;
11.     public RectTransform center;
12.  
13.     private bool dragging = false;
14.     private int bttnDistance;
15.     private int minButtomNum;
16.     private int bttnLength;
17.  
18.     public float[] distance;
19.  
20.     public float[] distReposition;
21.  
22.     // Cache references to the Button and Text components of each button
23.     private RectTransform[] buttonRectTransforms;
24.     private Text[] buttonTexts;
25.     private Image[] buttonImages;
26.  
27.     private void Start()
28.     {
29.         bttnLength = bttn.Length;
30.  
31.         distance = new float[bttnLength];
32.         distReposition = new float[bttnLength];
33.  
34.         buttonRectTransforms = new RectTransform[bttnLength];
35.         buttonTexts = new Text[bttnLength];
36.         buttonImages = new Image[bttnLength];
37.  
38.         for (int i = 0; i < bttnLength; i++)
39.         {
40.             buttonRectTransforms[i] = bttn[i].GetComponent<RectTransform>();
41.             buttonTexts[i] = bttn[i].GetComponentInChildren<Text>();
42.             buttonImages[i] = bttn[i].GetComponent<Image>();
43.         }
44.  
45.         bttnDistance =
46.             (int)
47.             Mathf
48.                 .Abs(buttonRectTransforms[1].anchoredPosition.y -
49.                 buttonRectTransforms[0].anchoredPosition.y);
50.     }
51.  
52.     private void Update()
53.     {
54.         for (int i = 0; i < bttnLength; i++)
55.         {
56.             distReposition[i] = buttonRectTransforms[i].position.y - center.GetComponent<RectTransform>().position.y;
57.             distance[i] = Mathf.Abs(distReposition[i]); //Caution
58.  
59.             // Calculate the target alpha value for the button
60.             float targetAlpha = 0.0f;
61.             Vector2 targetScale = new Vector2(0.7f, 0.7f);
62.  
63.             if (distance[i] <= 50.0f)
64.             {
65.                 // If the button is within 300 units of the center, set the target alpha value to 1
66.                 targetAlpha = 1.0f;
67.                 targetScale = Vector2.one;
68.             }
69.             else if (distance[i] <= 350.0f)
70.             {
71.                 // If the button is within 600 units of the center, set the target alpha value to 0.5
72.                 targetAlpha = 0.4f;
73.                 targetScale = new Vector2(0.7f, 0.7f);
74.             }
75.  
76.             // Calculate the current alpha value for the button using lerp
77.             float currentAlpha = Mathf.Lerp(buttonTexts[i].color.a, targetAlpha, Time.deltaTime * 10.0f);
78.  
79.             Vector2 currentScale = Vector2.Lerp(buttonRectTransforms[i].localScale, targetScale, Time.deltaTime * 10.0f);
80.  
81.             // Set the alpha value of the button's text and image
82.             Color textColor = buttonTexts[i].color;
83.             textColor.a = currentAlpha;
84.             buttonTexts[i].color = textColor;
85.  
86.             Color imageColor = buttonImages[i].color;
87.             imageColor.a = currentAlpha;
88.             buttonImages[i].color = imageColor;
89.  
90.             buttonRectTransforms[i].localScale = currentScale;
91.  
92.             // Check if the button is out of view and reposition it if necessary
93.             if (distReposition[i] > 700)
94.             {
95.                 // Move the button to the bottom of the panel
96.                 buttonRectTransforms[i].anchoredPosition += new Vector2(0, -bttnLength * bttnDistance);
97.             }
98.             else if (distReposition[i] < -700)
99.             {
100.                 // Move the button to the top of the panel
101.                 buttonRectTransforms[i].anchoredPosition += new Vector2(0, bttnLength * bttnDistance);
102.             }
103.         }
104.  
105.  
106.         float minDistance = Mathf.Min(distance);
107.  
108.         for (int a = 0; a < bttn.Length; a++)
109.         {
110.             if(minDistance == distance[a])
111.             {
112.                 minButtomNum = a;
113.             }
114.         }
115.  
116.         if(!dragging)
117.         {
118.             //LerpToBttn(minButtomNum * bttnDistance); //negative or positive value
119.             LerpToBttn(-bttn[minButtomNum].GetComponent<RectTransform>().anchoredPosition.y);
120.         }
121.     }
122.  
123.     void LerpToBttn(float position)
124.     {
125.         float newY = Mathf.Lerp(panel.anchoredPosition.y, position, Time.deltaTime * 15f);
126.         Vector2 newPosition = new Vector2(panel.anchoredPosition.x, newY);
127.  
128.         panel.anchoredPosition = newPosition;
129.     }
130.  
131.     public void StartDrag()
132.     {
133.         dragging = true;
134.     }
135.  
136.     public void EndDrag()
137.     {
138.         dragging = false;
139.     }
140. }
141.