Unity3D技术之跟踪已下载资源包浅析

狂风大尉

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：

1. <pre class="">using UnityEngine;
   
2. using System;
   
3. using System.Collections;
   
4. using System.Collections.Generic;
   
5. 
   
6. static public class AssetBundleManager {
   
7. // A dictionary to hold the AssetBundle references
   
8. static private Dictionary<string, AssetBundleRef> dictAssetBundleRefs;
   
9. static AssetBundleManager (){
   
10. dictAssetBundleRefs = new Dictionary<string, AssetBundleRef>();
    
11.    }
    
12. // Class with the AssetBundle reference, url and version
    
13. private class AssetBundleRef {
    
14. public AssetBundle assetBundle = null;
    
15. public int version;
    
16. public string url;
    
17. public AssetBundleRef(string strUrlIn, int intVersionIn) {
    
18. url = strUrlIn;
    
19. version = intVersionIn;
    
20.        }
    
21.    };
    
22. // Get an AssetBundle
    
23. public static AssetBundle getAssetBundle (string url, int version){
    
24. string keyName = url + version.ToString();
    
25. AssetBundleRef abRef;
    
26. if (dictAssetBundleRefs.TryGetValue(keyName, out abRef))
    
27. return abRef.assetBundle;
    
28. else
    
29. return null;
    
30.    }
    
31. // Download an AssetBundle
    
32. public static IEnumerator downloadAssetBundle (string url, int version){
    
33. string keyName = url + version.ToString();
    
34. if (dictAssetBundleRefs.ContainsKey(keyName))
    
35. yield return null;
    
36. else {
    
37. using(WWW www = WWW.LoadFromCacheOrDownload (url, version)){
    
38. yield return www;
    
39. if (www.error != null)
    
40. throw new Exception("WWW download:"+ www.error);
    
41. AssetBundleRef abRef = new AssetBundleRef (url, version);
    
42. abRef.assetBundle = www.assetBundle;
    
43. dictAssetBundleRefs.Add (keyName, abRef);
    
44.            }
    
45.        }
    
46.    }
    
47. // Unload an AssetBundle
    
48. public static void Unload (string url, int version, bool allObjects){
    
49. string keyName = url + version.ToString();
    
50. AssetBundleRef abRef;
    
51. if (dictAssetBundleRefs.TryGetValue(keyName, out abRef)){
    
52. abRef.assetBundle.Unload (allObjects);
    
53. abRef.assetBundle = null;
    
54. dictAssetBundleRefs.Remove(keyName);
    
55.        }
    
56.    }
    
57. }</pre><p style="margin-bottom: 15px;">An example usage of the class would be:</p><pre>using UnityEditor;
    
58. 
    
59. class ManagedAssetBundleExample :MonoBehaviour {
    
60. public string url;
    
61. public int version;
    
62. AssetBundle bundle;
    
63. void OnGUI (){
    
64. if (GUILayout.Label ("Download bundle"){
    
65. bundle = AssetBundleManager.getAssetBundle (url, version);
    
66. if(!bundle)
    
67. StartCoroutine (DownloadAB());
    
68.        }
    
69.    }
    
70. IEnumerator DownloadAB (){
    
71. yield return StartCoroutine(AssetBundleManager.downloadAssetBundle (url, version));
    
72. bundle = AssetBundleManager.getAssetBundle (url, version);
    
73.    }
    
74. void OnDisable (){
    
75. AssetBundleManager.Unload (url, version);
    
76.    }
    
77. }</pre>

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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)。

hariboot

Thanks for sharing！

tianhett

感谢分享。。。。