标签：assetbundle   依赖   dependencies   增量更新   unity   

首先我们来看一下官方Build AssetBundle的示例代码：

// C# Example
	// Builds an asset bundle from the selected objects in the project view.
	// Once compiled go to "Menu" -> "Assets" and select one of the choices
	// to build the Asset Bundle
	
	using UnityEngine;
	using UnityEditor;
	public class ExportAssetBundles {
		[MenuItem("Assets/Build AssetBundle From Selection - Track dependencies")]
		static void ExportResource () {
			// Bring up save panel
			string path = EditorUtility.SaveFilePanel ("Save Resource", "", "New Resource", "unity3d");
			if (path.Length != 0) {
				// Build the resource file from the active selection.
				Object[] selection = Selection.GetFiltered(typeof(Object), SelectionMode.DeepAssets);
				BuildPipeline.BuildAssetBundle(Selection.activeObject, selection, path, 
                                  BuildAssetBundleOptions.CollectDependencies | BuildAssetBundleOptions.CompleteAssets);
				Selection.objects = selection;
			}
		}
		[MenuItem("Assets/Build AssetBundle From Selection - No dependency tracking")]
		static void ExportResourceNoTrack () {
			// Bring up save panel
			string path = EditorUtility.SaveFilePanel ("Save Resource", "", "New Resource", "unity3d");
			if (path.Length != 0) {
				// Build the resource file from the active selection.
				BuildPipeline.BuildAssetBundle(Selection.activeObject, Selection.objects, path);
			}
		}
	}

1. uild AssetBundle From Selection - Track dependencies. This will build the current object into an asset bundle and include all of its dependencies. For example if you have a prefab that consists of several hierarchical layers then it will recursively add all the child objects and components to the asset bundle.

2. Build AssetBundle From Selection - No dependency tracking. This is the opposite of the previous method and will only include the single asset you have selected.

其实官方的这个示例代码中No dependency tracking 这一段是有问题的，如果使用官方的这段代码，不管是否选择自动打包依赖，依赖的相关内容都会打包到最终的assetBundle中去。这是因为BuildPipleLine.BuildAssetBundle接口的默认的BuildAssetBundleOptions参数为：BuildAssetBundleOptions.CollectDependencies | BuildAssetBundleOptions.CompleteAssets。 我们看官方的定义：

static function BuildAssetBundle(mainAsset: Object, assets: Object[], pathName: string, assetBundleOptions: BuildAssetBundleOptions = BuildAssetBundleOptions.CollectDependencies | BuildAssetBundleOptions.CompleteAssets, targetPlatform: BuildTarget = BuildTarget.WebPlayer): bool;

所以我们如果不想自动打包依赖项，需要手动传入不带BuildAssetBundleOptions.CollectDependencies的BuildAssetBundleOptions，如

BuildPipeline.BuildAssetBundle(Selection.activeObject, Selection.objects, path,BuildAssetBundleOptions.CompleteAssets);

一般我们打包assetbundle的时候，会选择自动打包依赖文件。但是这样会有一个问题，也就是说如果多个对象存在对同一个依赖对象的引用的话，会导致存在多份依赖对象，对包体和内存都有影响。这里我们可以使用Unity提供的依赖管理来进行打包，我们来看下官方的示例代码

using UnityEngine;
using UnityEditor;

public class Exporter : MonoBehaviour {
    
    [MenuItem("Assets/Export all asset bundles")]
    static void Export() {
        BuildAssetBundleOptions options = 
            BuildAssetBundleOptions.CollectDependencies | 
            BuildAssetBundleOptions.CompleteAssets | 
            BuildAssetBundleOptions.DeterministicAssetBundle;
        
        BuildPipeline.PushAssetDependencies();
        BuildPipeline.BuildAssetBundle(AssetDatabase.LoadMainAssetAtPath("Assets/ShadersList.prefab"), null, "WebPlayer/ShadersList.unity3d", options);
            
        BuildPipeline.PushAssetDependencies();
        BuildPipeline.BuildAssetBundle(AssetDatabase.LoadMainAssetAtPath("Assets/Scene1.prefab"), null, "WebPlayer/Scene1.unity3d", options);
        BuildPipeline.BuildAssetBundle(AssetDatabase.LoadMainAssetAtPath("Assets/Scene2.prefab"), null, "WebPlayer/Scene2.unity3d", options);       
        
        BuildPipeline.PopAssetDependencies();
        BuildPipeline.PopAssetDependencies();
    }
    
    [MenuItem("Assets/Update shader bundle")]
    static void ExportShaders() {
        BuildAssetBundleOptions options = 
            BuildAssetBundleOptions.CollectDependencies | 
            BuildAssetBundleOptions.CompleteAssets | 
            BuildAssetBundleOptions.DeterministicAssetBundle;
        
        BuildPipeline.PushAssetDependencies();
        BuildPipeline.BuildAssetBundle(AssetDatabase.LoadMainAssetAtPath("Assets/ShadersList.prefab"), null, "WebPlayer/ShadersList.unity3d", options);
        
        BuildPipeline.PopAssetDependencies();
    }
}

1、对于资源文件，其实我们光加载到内存还不行（类似：WWW asset = new WWW(BundleURL + "res.assetbundle")），我们需要手动调用：AssetBundle bundle = asset.assetBundle;否者后续加载其他的assetbundle会资源丢失，这是为什么呢？我们再来看看官方关于www.assetBundle的定义：

Streams an AssetBundle that can contain any kind of asset from the project folder.

这里解释的其实不好理解，这里应该是通过调用www.assetbundle来将assetbundle的assetbundle的映射结构加载到内存。（WebStream中一共分为三块，Assetbundle原始压缩数据、Decompression Buffer以及Assetbundle的解压数据。WebStream中的仅是数据流，而Assets中的资源则是通过Assetbundle.Load加载出来的真正可被引擎识别的资源，比如Texture2D、Mesh等，所以我们需要将webStrem转换成能够识别的资源，以供系统后续load）。

2、对于一般的Assetbundle，我们通常会调用assetBundle.Unload(false)来释放内存中的AssetBundle的原始数据。但是对于资源文件，我们又不能这样操作了。我们先来看下官方关于Unload的定义：

参考：

http://docs.unity3d.com/Manual/AssetBundlesIntro.html

http://forum.china.unity3d.com/thread-379-1-1.html

AssetBundle杂谈

标签：assetbundle   依赖   dependencies   增量更新   unity   

原文地址：http://blog.csdn.net/cubesky/article/details/40895269