UICollection.cs

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See LICENSE in the project root for license information.

using System.Collections.Generic;
using UnityEngine;

namespace HoloToolkit.UI.Keyboard
{
    [AddComponentMenu("UI/HoloUIKit/UICollection")]
    [RequireComponent(typeof(RectTransform))]
    [ExecuteInEditMode]
    public class UICollection : MonoBehaviour
    {
        public float MaxWidth = -1.0f;

        public float MaxHeight = -1.0f;

        public float HorizontalSpacing = 0.0f;

        public float VerticalSpacing = 0.0f;

        public List<RectTransform> Items { get; private set; }

        private RectTransform rectTransform;

        private void Awake()
        {
            Items = new List<RectTransform>();
        }

        // Use this for initialization
        private void Start()
        {
            // Verify this is attached to a GameObject with a rect transform
            rectTransform = GetComponent<RectTransform>();

            if (!Application.isEditor) { return; }

            // Collect children items already added (likely added in the Editor)
            CollectItems();
            UpdateLayout();
        }

        private void Update()
        {
            if (!Application.isEditor) { return; }
            CollectItems();
            UpdateLayout();
        }

        public void AddItem(RectTransform item)
        {
            Items.Add(item);

            item.SetParent(transform);
            item.transform.localScale = Vector3.one;
            item.position = Vector3.zero;
            item.anchoredPosition3D = Vector3.zero;

            UpdateLayout();
        }

        public void RemoveItem(RectTransform item)
        {
            Items.Remove(item);

            UpdateLayout();
        }

        public void RemoveAllItems()
        {
            Items.Clear();

            UpdateLayout();
        }

        private void CollectItems()
        { 
            Items.Clear();

            foreach (Transform childTransform in transform)
            {
                RectTransform childRect = childTransform.GetComponent<RectTransform>();
                if (childRect != null)
                {
                    AddItem(childRect);
                }
            }
        }

        protected virtual void UpdateLayout()
        {
            Rect rect = rectTransform.rect;

            Vector2 updatedSize = Vector2.zero;
            if (MaxWidth < 0.0f)
            {
                // Set to the width of the panel
                updatedSize.x = rect.width;
            }
            else
            {
                // Set to the max width
                updatedSize.x = MaxWidth;
            }

            if (MaxHeight < 0.0f)
            {
                // Set to the height of the panel
                updatedSize.y = rect.height;
            }
            else
            {
                // Set to the max height
                updatedSize.y = MaxHeight;
            }

            Vector2 currentOffset = Vector2.zero;
            Vector2 anchorVec = Vector2.up;

            float columnHeight = 0.0f;
            float maxPanelWidth = 0.0f;

            for (int i = 0; i < Items.Count; i++)
            {

                // Ensure the anchors and pivot are set properly for positioning in the UICollection
                Items[i].anchorMin = anchorVec;
                Items[i].anchorMax = anchorVec;
                Items[i].pivot = anchorVec;

                columnHeight = Mathf.Max(Items[i].rect.height, columnHeight);

                if (Items[i].rect.width + currentOffset.x > updatedSize.x)
                {
                    // Move to next column
                    currentOffset.y += columnHeight + VerticalSpacing;
                    currentOffset.x = 0.0f;
                    columnHeight = Items[i].rect.height;

                    // Check to see if it can fit in the next column
                    if (Items[i].rect.height + currentOffset.y > updatedSize.y)
                    {
                        // Bail out... can't fit any more items!!!
                        break;
                    }
                }

                // Position item
                Items[i].anchoredPosition = new Vector2(currentOffset.x, -currentOffset.y);

                // Update current offset
                currentOffset.x += Items[i].rect.width + HorizontalSpacing;

                maxPanelWidth = Mathf.Max(currentOffset.x - HorizontalSpacing, maxPanelWidth);
            }

            // Update the panel size
            float finalWidth = MaxWidth < 0.0f ? rect.width : maxPanelWidth;
            float finalHeight = MaxHeight < 0.0f ? rect.height : columnHeight + currentOffset.y;
            rectTransform.sizeDelta = new Vector2(finalWidth, finalHeight);
        }
    }
}