Question

跟踪已下载资源包

Unity 一次只允许加载一个特定资源包 (AssetBundle) 实例到应用程序中。这意味着您无法检索 WWW 对象中之前已加载的相同资源包 (AssetBundle) 或尚未加载的资源包。实际上，这意味着您尝试访问之前已下载的如下资源包 (AssetBundle) 时：

AssetBundle bundle = www.assetBundle;

程序将引出以下错误

Cannot load cached AssetBundle.A file of the same name is already loaded from another AssetBundle

且资源包属性将返回 null。如果第一次下载时下载了该资源包 (AssetBundle)，则第二次下载时无法检索到该资源包，因此，无需再使用该资源包时，可以将其卸载 或获取其引用，并在它存在于内存中时避免将其下载。可根据需求决定需要采取的相应措施，但我们建议在加载完对象后立即卸载该资源包 (AssetBundle)。这可释放内存空间，并且不会再收到有关加载已缓存资源包 (AssetBundles) 的错误。

如需跟踪已下载资源包 (AssetBundles)，可使用包装类协助管理下载，如下：

using UnityEngine;
using System;
using System.Collections;
using System.Collections.Generic;

static public class AssetBundleManager {
// A dictionary to hold the AssetBundle references
static private Dictionary<string, AssetBundleRef> dictAssetBundleRefs;
static AssetBundleManager (){
dictAssetBundleRefs = new Dictionary<string, AssetBundleRef>();
   }
// Class with the AssetBundle reference, url and version
private class AssetBundleRef {
public AssetBundle assetBundle = null;
public int version;
public string url;
public AssetBundleRef(string strUrlIn, int intVersionIn) {
url = strUrlIn;
version = intVersionIn;
       }
   };
// Get an AssetBundle
public static AssetBundle getAssetBundle (string url, int version){
string keyName = url + version.ToString();
AssetBundleRef abRef;
if (dictAssetBundleRefs.TryGetValue(keyName, out abRef))
return abRef.assetBundle;
else
return null;
   }
// Download an AssetBundle
public static IEnumerator downloadAssetBundle (string url, int version){
string keyName = url + version.ToString();
if (dictAssetBundleRefs.ContainsKey(keyName))
yield return null;
else {
using(WWW www = WWW.LoadFromCacheOrDownload (url, version)){
yield return www;
if (www.error != null)
throw new Exception("WWW download:"+ www.error);
AssetBundleRef abRef = new AssetBundleRef (url, version);
abRef.assetBundle = www.assetBundle;
dictAssetBundleRefs.Add (keyName, abRef);
           }
       }
   }
// Unload an AssetBundle
public static void Unload (string url, int version, bool allObjects){
string keyName = url + version.ToString();
AssetBundleRef abRef;
if (dictAssetBundleRefs.TryGetValue(keyName, out abRef)){
abRef.assetBundle.Unload (allObjects);
abRef.assetBundle = null;
dictAssetBundleRefs.Remove(keyName);
       }
   }
}

An example usage of the class would be:

using UnityEditor;

class ManagedAssetBundleExample :MonoBehaviour {
public string url;
public int version;
AssetBundle bundle;
void OnGUI (){
if (GUILayout.Label ("Download bundle"){
bundle = AssetBundleManager.getAssetBundle (url, version);
if(!bundle)
StartCoroutine (DownloadAB());
       }
   }
IEnumerator DownloadAB (){
yield return StartCoroutine(AssetBundleManager.downloadAssetBundle (url, version));
bundle = AssetBundleManager.getAssetBundle (url, version);
   }
void OnDisable (){
AssetBundleManager.Unload (url, version);
   }
}

请记住，本示例中的 AssetBundleManager 类是静态的，正在引用的任何资源包 (AssetBundles) 不会在加载新场景时销毁。请将此类当做指南例程，但正如最初建议的那样，最好在使用后立即卸载资源包 (AssetBundles)。您始终可以克隆之前实例化的对象，无需再下载该资源包 (AssetBundles)。

返回资源包 (AssetBundles) 简介