SpriteManager.cs

using UnityEngine;
using UnityEngine.UI;
using System.Collections.Generic;
using NUnit.Framework;

// LINK: http://answers.unity3d.com/questions/736237/how-to-load-sprite-at-runtime-from-atlas.html
public class SpriteManager : SingletonBehaviour<SpriteManager>
{
	[SerializeField] List<Sprite> ReticleSprites = new List<Sprite>();
	[SerializeField] List<Sprite> ItemSprites = new List<Sprite>();
	[SerializeField] List<Sprite> HelpUISprites = new List<Sprite>();

	Dictionary<string, Sprite> spriteDict;

	// copy list into dict for faster lookup
	void Awake()
	{
		Assert.Greater(ReticleSprites.Count, 0);
		Assert.Greater(ItemSprites.Count, 0);
		Assert.Greater(HelpUISprites.Count, 0);

		var spriteCount = ReticleSprites.Count + ItemSprites.Count + HelpUISprites.Count;
		spriteDict = new Dictionary<string, Sprite>(spriteCount);

		addSpriteListToDict(ReticleSprites, "ReticleSprites");
		addSpriteListToDict(ItemSprites, "ItemSprites");
		addSpriteListToDict(HelpUISprites, "HelpUISprites");
	}

	public Sprite GetSprite(string spriteName)
	{
		Sprite sprite;
		if(!spriteDict.TryGetValue(spriteName, out sprite))
		{
			Debug.LogWarning(string.Format("SpriteCollection.GetSprite: no sprite found for key {0}, returning null", spriteName));
			return null;
		}
		return sprite;
	}

	void addSpriteListToDict(IList<Sprite> spriteList, string listName)
	{
		for (int i = 0; i < spriteList.Count; i++)
		{
			Sprite sprite = spriteList[i];
			if(sprite == null)
			{
				Debug.Log(string.Format("SpriteCollection.addSpriteListToDict: slot {0} empty in sprite list {1}, continuing", i, listName));
				continue;
			}
			Assert.False(spriteDict.ContainsKey(sprite.name), "duplicate sprite name (" + sprite.name + ")");
			spriteDict.Add(sprite.name, sprite);
		}
	}
}