Unity AssetBundle 设置名称优化

原因

在大部分的 Unity 分析打包 AssetBundle 过程中，是采用对资源设置 AssetBundle 名称标签的方式来进行打包，类似如下：

public static void SetBundleName(string assetPath, string bundleName)
{
    var importer = AssetImporter.GetAtPath(assetPath);
    if (importer && importer.assetBundleName != bundleName)
    {
        importer.assetBundleName = bundleName;
    }
}

private static void BuildAssetBundlesInter(string outputPath, AssetBundleBuildOptions options)
{
    AssetBundleManifest manifest = BuildPipeline.BuildAssetBundles(outputPath,
                BuildAssetBundleOptions.UncompressedAssetBundle, GetBuildTarget());
}

每设置一个资源的 AssetBundle 名称，都会导致 Unity 写入其 .meta 文件，这样在分析的过程耗费不少时间。而且在打包完毕，又得重新设置所有资源的 AssetBundle 名称为空，否则仓库会提示有文件变化。

思路

修改流程，改成传入 AssetBundleBuild[] 的方式进行打包，这样就无需设置资源的 AssetBundle 名称。但是不能简单的把结果保存为 AssetBundleBuild[] 数组对象，因为打包工具支持当次不再分析资源，直接使用上一次的分析结果。所以要把 AssetBundleBuild[] 结果存为临时文件，方便下次使用，正常来说，这个临时文件一般只对当天的资源有效即可，当更新了资源，肯定得重新分析资源，不能再使用上次的结果。所以，只需要把这临时文件放在 Temp 目录下即可。

解决

创建一个独立类，来管理分析的 AssetBundle 构建信息：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization.Formatters.Binary;
using UnityEditor;

/// 

/// AssetBundle 分析映射
/// 
public static class AssetBundleBuildMap
{
    private static AssetBundleMap assetBundleMap;

    public static void Clear()
    {
        if (assetBundleMap != null)
        {
            assetBundleMap = null;
        }
    }

    /// 

    /// 普通资源设置 AssetBundle 名称接口
    /// 
    /// 
    /// 
    public static void SetAssetPathAssetBundleName(string assetPath, string assetBundleName)
    {
        if (assetBundleMap == null)
        {
            assetBundleMap = new AssetBundleMap();
        }
        assetBundleMap.AddMap(assetPath, assetBundleName);
    }

    public static bool IsAssetPathHasAssetBundleName(string assetPath)
    {
        if (assetBundleMap == null)
        {
            return false;
        }
        return assetBundleMap.assetPathSet.Contains(assetPath);
    }

    public static List<string> GetAllAssetBundleNames()
    {
        if (assetBundleMap == null)
        {
            return null;
        }
        List<string> allAssetBundleNames = assetBundleMap.assetBundleDict.Keys.ToList();
        allAssetBundleNames.Sort(EditorUtility.NaturalCompare);
        return allAssetBundleNames;
    }

    public static List<string> GetAssetPathsFromAssetBundle(string assetBundleName)
    {
        if (assetBundleMap == null)
        {
            return null;
        }
        List<string> assetPaths;
        if (assetBundleMap.assetBundleDict.TryGetValue(assetBundleName, out assetPaths))
        {
            assetPaths.Sort(EditorUtility.NaturalCompare);
            return assetPaths;
        }
        return null;
    }

    /// 

    /// 最终需要进行打包的资产构建列表
    /// 
    /// 
    public static AssetBundleBuild[] GetAssetBundleBuilds()
    {
        List assetBundleBuilds = new List();
        string tempPath = "Temp/AssetBundleBuildAnalyze";
        if (assetBundleMap == null)
        {
            assetBundleMap = AssetBundleMap.MakeByLoad(tempPath);
        }
        else
        {
            assetBundleMap.Save(tempPath);
        }
        assetBundleBuilds.AddRange(assetBundleMap.GetBuilds());

        return assetBundleBuilds.ToArray();
    }

    private class AssetBundleMap
    {
        public readonly HashSet<string> assetPathSet = new HashSet<string>();
        public Dictionary<string, List<string>> assetBundleDict = new Dictionary<string, List<string>>();

        public void AddMap(string assetPath, string assetBundleName)
        {
            if (string.IsNullOrEmpty(assetPath) || string.IsNullOrEmpty(assetBundleName))
            {
                return;
            }
            if (assetPathSet.Contains(assetPath))
            {
                return;
            }

            assetPathSet.Add(assetPath);
            List<string> assetPaths;
            if (assetBundleDict.TryGetValue(assetBundleName, out assetPaths))
            {
                assetPaths.Add(assetPath);
            }
            else
            {
                assetPaths = new List<string> { assetPath };
                assetBundleDict.Add(assetBundleName, assetPaths);
            }
        }

        public List GetBuilds()
        {
            List assetBundleBuilds = new List();
            foreach (var kv in assetBundleDict)
            {
                assetBundleBuilds.Add(new AssetBundleBuild() { assetBundleName = kv.Key, assetNames = kv.Value.ToArray() });
            }
            return assetBundleBuilds;
        }

        public void Save(string tempPath)
        {
            using (MemoryStream stream = new MemoryStream())
            {
                new BinaryFormatter().Serialize(stream, assetBundleDict);
                File.WriteAllBytes(tempPath, stream.ToArray());
            }
        }

        public static AssetBundleMap MakeByLoad(string tempPath)
        {
            AssetBundleMap map = new AssetBundleMap();
            if (File.Exists(tempPath))
            {
                byte[] bytes = File.ReadAllBytes(tempPath);
                using (MemoryStream stream = new MemoryStream(bytes))
                {
                    map.assetBundleDict = new BinaryFormatter().Deserialize(stream) as Dictionary<string, List<string>>;
                }
            }
            return map;
        }
    }
}

最终调用的方式如下：

private static void BuildAssetBundlesInter(string outputPath, AssetBundleBuildOptions options)
{
    AssetBundleBuild[] assetBundleBuilds = AssetBundleBuildMap.GetAssetBundleBuilds();

    AssetBundleManifest manifest = BuildPipeline.BuildAssetBundles(outputPath, assetBundleBuilds,
            BuildAssetBundleOptions.UncompressedAssetBundle, GetBuildTarget());
    AssetBundleBuildMap.Clear();
}