How to scroll to a specific element in ScrollRect with Unity UI? - user-interface

Question

I built a registration form for a mobile game using Unity 5.1.
To do that, I use Unity UI components: ScrollRect + Autolayout (Vertical layout) + Text (labels) + Input Field.
This part works fine.
But, when keyboard is opened, the selected field is under keyboard. Is there a way to programmatically scroll the form to bring the selected field into view?
I have tried using ScrollRect.verticalNormalizedPosition and it works fine to scroll some, however I am not able to make selected field appear where I want.
Thanks for your help !

Answer 1

I am going to give you a code snippet of mine because I feel like being helpful. Hope this helps!
protected ScrollRect scrollRect;
protected RectTransform contentPanel;
public void SnapTo(RectTransform target)
{
Canvas.ForceUpdateCanvases();
contentPanel.anchoredPosition =
(Vector2)scrollRect.transform.InverseTransformPoint(contentPanel.position)
- (Vector2)scrollRect.transform.InverseTransformPoint(target.position);
}

Answer 2

None of the suggestions worked for me, the following code did
Here is the extension
using UnityEngine;
using UnityEngine.UI;
namespace BlinkTalk
{
public static class ScrollRectExtensions
{
public static Vector2 GetSnapToPositionToBringChildIntoView(this ScrollRect instance, RectTransform child)
{
Canvas.ForceUpdateCanvases();
Vector2 viewportLocalPosition = instance.viewport.localPosition;
Vector2 childLocalPosition = child.localPosition;
Vector2 result = new Vector2(
0 - (viewportLocalPosition.x + childLocalPosition.x),
0 - (viewportLocalPosition.y + childLocalPosition.y)
);
return result;
}
}
}
And here is how I used it to scroll a direct child of the content into view
private void Update()
{
MyScrollRect.content.localPosition = MyScrollRect.GetSnapToPositionToBringChildIntoView(someChild);
}

Answer 3

Although #maksymiuk's answer is the most correct one, as it properly takes into account anchors, pivot and all the rest thanks to InverseTransformPoint() function, it still didn't work out-of-box for me - for vertical scroller, it was changing its X position too. So I just made change to check if vertical or horizontal scroll is enabled, and not change their axis if they aren't.
public static void SnapTo( this ScrollRect scroller, RectTransform child )
{
Canvas.ForceUpdateCanvases();
var contentPos = (Vector2)scroller.transform.InverseTransformPoint( scroller.content.position );
var childPos = (Vector2)scroller.transform.InverseTransformPoint( child.position );
var endPos = contentPos - childPos;
// If no horizontal scroll, then don't change contentPos.x
if( !scroller.horizontal ) endPos.x = contentPos.x;
// If no vertical scroll, then don't change contentPos.y
if( !scroller.vertical ) endPos.y = contentPos.y;
scroller.content.anchoredPosition = endPos;
}

Answer 4

here's the way I clamped selected object into ScrollRect
private ScrollRect scrollRect;
private RectTransform contentPanel;
public void ScrollReposition(RectTransform obj)
{
var objPosition = (Vector2)scrollRect.transform.InverseTransformPoint(obj.position);
var scrollHeight = scrollRect.GetComponent<RectTransform>().rect.height;
var objHeight = obj.rect.height;
if (objPosition.y > scrollHeight / 2)
{
contentPanel.localPosition = new Vector2(contentPanel.localPosition.x,
contentPanel.localPosition.y - objHeight - Padding.top);
}
if (objPosition.y < -scrollHeight / 2)
{
contentPanel.localPosition = new Vector2(contentPanel.localPosition.x,
contentPanel.localPosition.y + objHeight + Padding.bottom);
}
}

Answer 5

The preconditions for my version of this problem:
The element I want to scroll to should be fully visible (with minimal clearance)
The element is a direct child of the scrollRect's content
Keep scoll position if element is already fully visible
I only care about the vertical dimension
This is what worked best for me (thanks for the other inspirations):
// ScrollRect scrollRect;
// RectTransform element;
// Fully show `element` inside `scrollRect` with at least 25px clearance
scrollArea.EnsureVisibility(element, 25);
Using this extension method:
public static void EnsureVisibility(this ScrollRect scrollRect, RectTransform child, float padding=0)
{
Debug.Assert(child.parent == scrollRect.content,
"EnsureVisibility assumes that 'child' is directly nested in the content of 'scrollRect'");
float viewportHeight = scrollRect.viewport.rect.height;
Vector2 scrollPosition = scrollRect.content.anchoredPosition;
float elementTop = child.anchoredPosition.y;
float elementBottom = elementTop - child.rect.height;
float visibleContentTop = -scrollPosition.y - padding;
float visibleContentBottom = -scrollPosition.y - viewportHeight + padding;
float scrollDelta =
elementTop > visibleContentTop ? visibleContentTop - elementTop :
elementBottom < visibleContentBottom ? visibleContentBottom - elementBottom :
0f;
scrollPosition.y += scrollDelta;
scrollRect.content.anchoredPosition = scrollPosition;
}

Answer 6

A variant of Peter Morris answer for ScrollRects which have movement type "elastic". It bothered me that the scroll rect kept animating for edge cases (first or last few elements). Hope it's useful:
/// <summary>
/// Thanks to https://stackoverflow.com/a/50191835
/// </summary>
/// <param name="instance"></param>
/// <param name="child"></param>
/// <returns></returns>
public static IEnumerator BringChildIntoView(this UnityEngine.UI.ScrollRect instance, RectTransform child)
{
Canvas.ForceUpdateCanvases();
Vector2 viewportLocalPosition = instance.viewport.localPosition;
Vector2 childLocalPosition = child.localPosition;
Vector2 result = new Vector2(
0 - (viewportLocalPosition.x + childLocalPosition.x),
0 - (viewportLocalPosition.y + childLocalPosition.y)
);
instance.content.localPosition = result;
yield return new WaitForUpdate();
instance.horizontalNormalizedPosition = Mathf.Clamp(instance.horizontalNormalizedPosition, 0f, 1f);
instance.verticalNormalizedPosition = Mathf.Clamp(instance.verticalNormalizedPosition, 0f, 1f);
}
It introduces a one frame delay though.
UPDATE: Here is a version which does not introduce a frame delay and it also takes scaling of the content into account:
/// <summary>
/// Based on https://stackoverflow.com/a/50191835
/// </summary>
/// <param name="instance"></param>
/// <param name="child"></param>
/// <returns></returns>
public static void BringChildIntoView(this UnityEngine.UI.ScrollRect instance, RectTransform child)
{
instance.content.ForceUpdateRectTransforms();
instance.viewport.ForceUpdateRectTransforms();
// now takes scaling into account
Vector2 viewportLocalPosition = instance.viewport.localPosition;
Vector2 childLocalPosition = child.localPosition;
Vector2 newContentPosition = new Vector2(
0 - ((viewportLocalPosition.x * instance.viewport.localScale.x) + (childLocalPosition.x * instance.content.localScale.x)),
0 - ((viewportLocalPosition.y * instance.viewport.localScale.y) + (childLocalPosition.y * instance.content.localScale.y))
);
// clamp positions
instance.content.localPosition = newContentPosition;
Rect contentRectInViewport = TransformRectFromTo(instance.content.transform, instance.viewport);
float deltaXMin = contentRectInViewport.xMin - instance.viewport.rect.xMin;
if(deltaXMin > 0) // clamp to <= 0
{
newContentPosition.x -= deltaXMin;
}
float deltaXMax = contentRectInViewport.xMax - instance.viewport.rect.xMax;
if (deltaXMax < 0) // clamp to >= 0
{
newContentPosition.x -= deltaXMax;
}
float deltaYMin = contentRectInViewport.yMin - instance.viewport.rect.yMin;
if (deltaYMin > 0) // clamp to <= 0
{
newContentPosition.y -= deltaYMin;
}
float deltaYMax = contentRectInViewport.yMax - instance.viewport.rect.yMax;
if (deltaYMax < 0) // clamp to >= 0
{
newContentPosition.y -= deltaYMax;
}
// apply final position
instance.content.localPosition = newContentPosition;
instance.content.ForceUpdateRectTransforms();
}
/// <summary>
/// Converts a Rect from one RectTransfrom to another RectTransfrom.
/// Hint: use the root Canvas Transform as "to" to get the reference pixel positions.
/// </summary>
/// <param name="from"></param>
/// <param name="to"></param>
/// <returns></returns>
public static Rect TransformRectFromTo(Transform from, Transform to)
{
RectTransform fromRectTrans = from.GetComponent<RectTransform>();
RectTransform toRectTrans = to.GetComponent<RectTransform>();
if (fromRectTrans != null && toRectTrans != null)
{
Vector3[] fromWorldCorners = new Vector3[4];
Vector3[] toLocalCorners = new Vector3[4];
Matrix4x4 toLocal = to.worldToLocalMatrix;
fromRectTrans.GetWorldCorners(fromWorldCorners);
for (int i = 0; i < 4; i++)
{
toLocalCorners[i] = toLocal.MultiplyPoint3x4(fromWorldCorners[i]);
}
return new Rect(toLocalCorners[0].x, toLocalCorners[0].y, toLocalCorners[2].x - toLocalCorners[1].x, toLocalCorners[1].y - toLocalCorners[0].y);
}
return default(Rect);
}

Answer 7

In case anyone looking for a smooth scroll (using lerp).
[SerializeField]
private ScrollRect _scrollRectComponent; //your scroll rect component
[SerializeField]
RectTransform _container; //content transform of the scrollrect
private IEnumerator LerpToChild(RectTransform target)
{
Vector2 _lerpTo = (Vector2)_scrollRectComponent.transform.InverseTransformPoint(_container.position) - (Vector2)_scrollRectComponent.transform.InverseTransformPoint(target.position);
bool _lerp = true;
Canvas.ForceUpdateCanvases();
while(_lerp)
{
float decelerate = Mathf.Min(10f * Time.deltaTime, 1f);
_container.anchoredPosition = Vector2.Lerp(_scrollRectComponent.transform.InverseTransformPoint(_container.position), _lerpTo, decelerate);
if (Vector2.SqrMagnitude((Vector2)_scrollRectComponent.transform.InverseTransformPoint(_container.position) - _lerpTo) < 0.25f)
{
_container.anchoredPosition = _lerpTo;
_lerp = false;
}
yield return null;
}
}

Answer 8

simple and works perfectly
var pos = 1 - ((content.rect.height / 2 - target.localPosition.y) / content.rect.height);
scrollRect.normalizedPosition = new Vector2(0, pos);

Answer 9

Yes,this is possible using coding to scroll vertically, please try this code :
//Set Scrollbar Value - For Displaying last message of content
Canvas.ForceUpdateCanvases ();
verticleScrollbar.value = 0f;
Canvas.ForceUpdateCanvases ();
This code working fine for me ,when i developed chat functionality.

Answer 10

width signifiy the width of childern in scroll rect (assuming that all childerns width is same), spacing signifies the space between childerns, index signifies the target element you want to reach
public float getSpecificItem (float pWidth, float pSpacing,int pIndex) {
return (pIndex * pWidth) - pWidth + ((pIndex - 1) * pSpacing);
}

Answer 11

Vertical adjustment:
[SerializeField]
private ScrollRect _scrollRect;
private void ScrollToCurrentElement()
{
var siblingIndex = _currentListItem.transform.GetSiblingIndex();
float pos = 1f - (float)siblingIndex / _scrollRect.content.transform.childCount;
if (pos < 0.4)
{
float correction = 1f / _scrollRect.content.transform.childCount;
pos -= correction;
}
_scrollRect.verticalNormalizedPosition = pos;
}

Answer 12

Here's what I created to solve this problem. Place this behavior on each button that can be selected via controller UI navigation.
It supports fully nested children objects.
It only supports vertical scrollrects, but can be easily adapted to do horizontal.
using UnityEngine;
using System;
using UnityEngine.EventSystems;
using UnityEngine.UI;
namespace Legend
{
public class ScrollToOnSelect: MonoBehaviour, ISelectHandler
{
ScrollRect scrollRect;
RectTransform target;
void Start()
{
scrollRect = GetComponentInParent<ScrollRect>();
target = (RectTransform)this.transform;
}
Vector3 LocalPositionWithinAncestor(Transform ancestor, Transform target)
{
var result = Vector3.zero;
while (ancestor != target && target != null)
{
result += target.localPosition;
target = target.parent;
}
return result;
}
public void EnsureScrollVisible()
{
Canvas.ForceUpdateCanvases();
var targetPosition = LocalPositionWithinAncestor(scrollRect.content, target);
var top = (-targetPosition.y) - target.rect.height / 2;
var bottom = (-targetPosition.y) + target.rect.height / 2;
var topMargin = 100; // this is here because there are headers over the buttons sometimes
var result = scrollRect.content.anchoredPosition;
if (result.y > top - topMargin)
result.y = top - topMargin;
if (result.y + scrollRect.viewport.rect.height < bottom)
result.y = bottom - scrollRect.viewport.rect.height;
//Debug.Log($"{targetPosition} {target.rect.size} {top} {bottom} {scrollRect.content.anchoredPosition}->{result}");
scrollRect.content.anchoredPosition = result;
}
public void OnSelect(BaseEventData eventData)
{
if (scrollRect != null)
EnsureScrollVisible();
}
}
}