// 从缓存中查找AssetBundle，没有则同步加载并缓存
public static AssetBundleRef GetAB(string assetbundleName)
{
AssetBundleRef abr;
if (abDict.TryGetValue(assetbundleName, out abr))
{
// 缓存命中
abr.Retain();
return(abr);
}
AssetBundle ab = AssetBundleLoader.Load(assetbundleName); // 同步加载
abr = AssetBundleManager.CacheAB(assetbundleName, ab);
CheckShouldCacheSprite(abr);
return(abr);
}