266 lines
12 KiB
C#
266 lines
12 KiB
C#
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#region Includes
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using UnityEngine;
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using UnityEngine.Events;
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using UnityEngine.EventSystems;
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using UnityEngine.UI;
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#endregion
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/// <summary>
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/// The PageScroller class manages scrolling within a PageSlider component.
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/// It handles user interaction for swiping between pages and snapping to the closest page on release.
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/// </summary>
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public class PageScroller : MonoBehaviour, IBeginDragHandler, IEndDragHandler
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{
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#region Variables
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[Header("Configuration")]
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/// <summary>
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/// Minimum delta drag required to consider a page change (normalized value between 0 and 1).
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/// </summary>
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[Tooltip("Minimum delta drag required to consider a page change (normalized value between 0 and 1)")]
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[SerializeField] private float _minDeltaDrag = 0.1f;
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/// <summary>
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/// Duration (in seconds) for the page snapping animation.
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/// </summary>
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[Tooltip("Duration (in seconds) for the page snapping animation")]
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[SerializeField] private float _snapDuration = 0.3f;
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[Header("Events")]
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/// <summary>
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/// Event triggered when a page change starts.
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/// The event arguments are the index of the current page and the index of the target page.
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/// </summary>
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[Tooltip("Event triggered when a page change starts: index current page, index of target page")]
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public UnityEvent<int, int> OnPageChangeStarted;
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/// <summary>
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/// Event triggered when a page change ends.
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/// The event arguments are the index of the current page and the index of the new active page.
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/// </summary>
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[Tooltip("Event triggered when a page change ends: index of the current page, index of the new active page")]
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public UnityEvent<int, int> OnPageChangeEnded;
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/// <summary>
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/// Gets the rectangle of the ScrollRect component used for scrolling.
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/// </summary>
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public Rect Rect
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{
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get
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{
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#if UNITY_EDITOR
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if (_scrollRect == null)
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{
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_scrollRect = FindScrollRect();
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}
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#endif
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return ((RectTransform)_scrollRect.transform).rect;
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}
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}
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/// <summary>
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/// Gets the RectTransform of the content being scrolled within the ScrollRect.
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/// </summary>
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public RectTransform Content
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{
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get
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{
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#if UNITY_EDITOR
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if (_scrollRect == null)
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{
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_scrollRect = FindScrollRect();
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}
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#endif
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return _scrollRect.content;
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}
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}
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private ScrollRect _scrollRect;
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private int _currentPage; // Index of the currently active page.
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private int _targetPage; // Index of the target page during a page change animation.
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private float _startNormalizedPosition; // Normalized position of the scroll bar when drag begins.
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private float _targetNormalizedPosition; // Normalized position of the scroll bar for the target page.
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private float _moveSpeed; // Speed of the scroll bar animation (normalized units per second).
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#endregion
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private void Awake()
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{
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_scrollRect = FindScrollRect();
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}
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private void Update()
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{
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// If there's no movement in progress (moveSpeed is 0), exit the function early.
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if (_moveSpeed == 0) { return; }
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// Get the current normalized position of the scroll rect (between 0 and 1).
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// Update the current position based on the move speed and deltaTime.
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var position = _scrollRect.horizontalNormalizedPosition;
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position += _moveSpeed * Time.deltaTime;
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// Determine the minimum and maximum allowed positions based on the move direction:
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// - If moving forward (positive moveSpeed): current position is the minimum, target position is the maximum.
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// - If moving backward (negative moveSpeed): current position is the maximum, target position is the minimum.
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// Clamp the current position to stay within the valid range (between min and max).
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var min = _moveSpeed > 0 ? position : _targetNormalizedPosition;
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var max = _moveSpeed > 0 ? _targetNormalizedPosition : position;
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position = Mathf.Clamp(position, min, max);
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// Update the actual position of the scroll rect in the ScrollRect component.
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_scrollRect.horizontalNormalizedPosition = position;
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// Check if the scroll rect has reached the target position (within a small tolerance using Mathf.Epsilon).
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if (Mathf.Abs(_targetNormalizedPosition - position) < Mathf.Epsilon)
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{
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// Stop the movement by setting moveSpeed to 0.
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_moveSpeed = 0;
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// Invoke the OnPageChangeEnded event to signal the completion of the page change animation.
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// The event arguments are the index of the previous page and the index of the new active page.
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OnPageChangeEnded?.Invoke(_currentPage, _targetPage);
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// Update the _currentPage variable to reflect the new active page.
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_currentPage = _targetPage;
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}
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}
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public void SetPage(int index)
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{
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_scrollRect.horizontalNormalizedPosition = GetTargetPagePosition(index);
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_targetPage = index;
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_currentPage = index;
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OnPageChangeEnded?.Invoke(0, _currentPage);
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}
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public void OnBeginDrag(PointerEventData eventData)
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{
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// Store the starting normalized position of the scroll bar.
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_startNormalizedPosition = _scrollRect.horizontalNormalizedPosition;
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// Check if the target page is different from the current page.
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if (_targetPage != _currentPage)
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{
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// If they are different, it means we were potentially in the middle of an animation
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// for a previous page change that got interrupted by this drag.
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// Therefore, signal the end of the previous page change animation (if any)
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// by invoking the OnPageChangeEnded event.
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// The event arguments are the index of the previous page (_currentPage)
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// and the index of the target page (_targetPage).
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OnPageChangeEnded?.Invoke(_currentPage, _targetPage);
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// Update the _currentPage variable to reflect the target page,
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// as this is now the intended page after the drag begins.
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_currentPage = _targetPage;
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}
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// Reset the move speed to 0 to stop any ongoing scroll animations.
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// This is necessary because a drag interaction might interrupt an ongoing page change animation.
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_moveSpeed = 0;
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}
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public void OnEndDrag(PointerEventData eventData)
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{
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// Calculate the width of a single page (normalized value between 0 and 1).
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// This is achieved by dividing 1 by the total number of pages.
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var pageWidth = 1f / GetPageCount();
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// Calculate the normalized position of the current page.
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// When snapping to a page, this position should ideally match the starting normalized position.
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var pagePosition = _currentPage * pageWidth;
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// Get the current normalized position of the scroll rect.
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var currentPosition = _scrollRect.horizontalNormalizedPosition;
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// Determine the minimum amount of drag required (normalized value) to consider a page change.
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// This is calculated by multiplying the page width by the _minDeltaDrag value.
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var minPageDrag = pageWidth * _minDeltaDrag;
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// Check if the drag direction is forward or backward.
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// This is determined by comparing the current position with the starting position.
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// A higher current position indicates a forward drag.
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var isForwardDrag = _scrollRect.horizontalNormalizedPosition > _startNormalizedPosition;
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// Calculate the normalized position where a page change should occur (switchPageBreakpoint).
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// This is calculated by adding (for forward drag) or subtracting (for backward drag)
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// the minimum page drag distance from the current page position.
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var switchPageBreakpoint = pagePosition + (isForwardDrag ? minPageDrag : -minPageDrag);
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// Determine if a page change should occur based on the current position and the switchPageBreakpoint.
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// If it's a forward drag and the current position is greater than the switchPageBreakpoint,
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// it means the user has dragged enough to switch to the next page.
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// Similarly, for a backward drag, if the current position is less than the switchPageBreakpoint,
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// a page change to the previous page is triggered.
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var page = _currentPage;
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if (isForwardDrag && currentPosition > switchPageBreakpoint)
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{
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page++;
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}
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else if (!isForwardDrag && currentPosition < switchPageBreakpoint)
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{
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page--;
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}
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// Call the ScrollToPage function to initiate the page change animation for the determined page.
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ScrollToPage(page);
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}
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/// <summary>
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/// This function handles initiating a page change animation based on a target page index
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/// during a scroll interaction. It calculates the target scroll position, determines if a page change
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/// is required based on drag distance and direction, and triggers the animation if necessary.
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/// </summary>
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/// <param name="page">The index of the target page to scroll to.</param>
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private void ScrollToPage(int page)
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{
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// Calculate the target normalized position for the scroll rect based on the target page index.
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_targetNormalizedPosition = GetTargetPagePosition(page);
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// Calculate the speed required to reach the target position within the snap duration.
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_moveSpeed = (_targetNormalizedPosition - _scrollRect.horizontalNormalizedPosition) / _snapDuration;
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// Update the target page variable to reflect the new target page.
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_targetPage = page;
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// If the target page is different from the current page,
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// invoke the OnPageChangeStarted event to signal the beginning of the page change animation.
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if (_targetPage != _currentPage)
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{
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OnPageChangeStarted?.Invoke(_currentPage, _targetPage);
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}
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}
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/// <summary>
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/// Calculates the number of scrollable pages in the scroll view, considering the content and viewport width.
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/// </summary>
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/// <returns>The number of scrollable pages.</returns>
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private int GetPageCount()
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{
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var contentWidth = _scrollRect.content.rect.width;
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var rectWidth = ((RectTransform)_scrollRect.transform).rect.size.x;
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return Mathf.RoundToInt(contentWidth / rectWidth) - 1;
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}
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private float GetTargetPagePosition(int page)
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{
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return page * (1f / GetPageCount());
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}
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private ScrollRect FindScrollRect()
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{
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var scrollRect = GetComponentInChildren<ScrollRect>();
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#if UNITY_EDITOR || DEVELOPMENT_BUILD
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if (scrollRect == null)
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{
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Debug.LogError("Missing ScrollRect in Children");
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}
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#endif
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return scrollRect;
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}
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}
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