unity AssetBudle 的引用计数（资源优化）

 首先写一个类包含ab和ab对应的引用以及对应的卸载方法，在写一个ab的管理类，包括全局ab的加载，卸载，以及相关根据引用数来判断是重内存中是否删除对应的依赖资源，是新建资源还是重内存中获取资源重而达到在ab适度颗粒话下的内存优化！

脚本：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System;
public class AssetBundleInfos
{
    public AssetBundle assetBundle;
    public int referencedCount;//引用数
    internal event Action unload;

    internal void OnUnload()
    {
        assetBundle.Unload(false);
        if (unload != null)
            unload();
    }
}
public class Resource_LoadManager
{
    AssetBundleManifest assetBundleManifest = null;
    Dictionary<string, string[]> dependencies = new Dictionary<string, string[]>();
    Dictionary<string, AssetBundleInfos> loadeAssetBundle = new Dictionary<string, AssetBundleInfos>();

    // Use this for initialization
    public Resource_LoadManager()
    {
        //Initalize();

    }

    //初始化加载所有的依赖项目
    public void Initalize()
    {
        AssetBundle bundle;
        switch (Application.platform)
        {
            case RuntimePlatform.Android:
                bundle = AssetBundle.LoadFromFile(System.IO.Path.Combine(DataPath, "Android"));