YooAsset源码阅读-Download

继续 YooAsset 的下载系统代码研究，本文将详细介绍如何创建下载器相关代码

CreateResourceDownloaderByAll

关键类

PlayModeImpl.cs
ResourceDownloaderOperation.cs
DownloaderOperation.cs
BundleInfo.cs

CreateResourceDownloaderByAll 方法用于创建下载所有需要更新资源的下载器。

关键源代码

// PlayModeImpl.cs Line 110-115
ResourceDownloaderOperation IPlayMode.CreateResourceDownloaderByAll(int downloadingMaxNumber, int failedTryAgain)
{
    List<BundleInfo> downloadList = GetDownloadListByAll(ActiveManifest);
    var operation = new ResourceDownloaderOperation(PackageName, downloadList, downloadingMaxNumber, failedTryAgain);
    return operation;
}

// PlayModeImpl.cs Line 245-264
public List<BundleInfo> GetDownloadListByAll(PackageManifest manifest)
{
    if (manifest == null)
        return new List<BundleInfo>();

    List<BundleInfo> result = new List<BundleInfo>(1000);
    foreach (var packageBundle in manifest.BundleList)
    {
        var fileSystem = GetBelongFileSystem(packageBundle);
        if (fileSystem == null)
            continue;

        if (fileSystem.NeedDownload(packageBundle))
        {
            var bundleInfo = new BundleInfo(fileSystem, packageBundle);
            result.Add(bundleInfo);
        }
    }
    return result;
}

流程图

flowchart TD
    A["CreateResourceDownloaderByAll"] -->|调用| B["GetDownloadListByAll"]
    B -->|遍历| C["manifest.BundleList"]
    C -->|每个Bundle| D["GetBelongFileSystem"]
    D -->|检查| E["fileSystem.NeedDownload"]
    E -->|是| F["创建BundleInfo"]
    E -->|否| G["跳过该Bundle"]
    F --> H["添加到下载列表"]
    G --> I["继续下一个Bundle"]
    H --> I
    I -->|所有Bundle处理完| J["返回下载列表"]
    J --> K["创建ResourceDownloaderOperation"]
    K --> L["返回下载器"]

    %% 样式定义
    style A fill:#ff6b6b,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#4ecdc4,stroke:#ffffff,stroke-width:2px,color:#000000
    style C fill:#45b7d1,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style D fill:#f9ca24,stroke:#ffffff,stroke-width:2px,color:#000000
    style E fill:#6c5ce7,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style F fill:#a29bfe,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style G fill:#fd79a8,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style H fill:#00d2d3,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style I fill:#ff9ff3,stroke:#ffffff,stroke-width:2px,color:#000000
    style J fill:#00aaff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style K fill:#ff3838,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style L fill:#2ed573,stroke:#ffffff,stroke-width:2px,color:#000000

CreateResourceDownloaderByTags

关键类

PlayModeImpl.cs
ResourceDownloaderOperation.cs
PackageBundle.cs

CreateResourceDownloaderByTags 方法用于创建下载指定标签资源的下载器，支持DLC（可下载内容）场景。

关键源代码

// PlayModeImpl.cs Line 116-121
ResourceDownloaderOperation IPlayMode.CreateResourceDownloaderByTags(string[] tags, int downloadingMaxNumber, int failedTryAgain)
{
    List<BundleInfo> downloadList = GetDownloadListByTags(ActiveManifest, tags);
    var operation = new ResourceDownloaderOperation(PackageName, downloadList, downloadingMaxNumber, failedTryAgain);
    return operation;
}

// PlayModeImpl.cs Line 265-297
public List<BundleInfo> GetDownloadListByTags(PackageManifest manifest, string[] tags)
{
    if (manifest == null)
        return new List<BundleInfo>();

    List<BundleInfo> result = new List<BundleInfo>(1000);
    foreach (var packageBundle in manifest.BundleList)
    {
        var fileSystem = GetBelongFileSystem(packageBundle);
        if (fileSystem == null)
            continue;

        if (fileSystem.NeedDownload(packageBundle))
        {
            // 如果未带任何标记，则统一下载
            if (packageBundle.HasAnyTags() == false)
            {
                var bundleInfo = new BundleInfo(fileSystem, packageBundle);
                result.Add(bundleInfo);
            }
            else
            {
                // 查询DLC资源
                if (packageBundle.HasTag(tags))
                {
                    var bundleInfo = new BundleInfo(fileSystem, packageBundle);
                    result.Add(bundleInfo);
                }
            }
        }
    }
    return result;
}

流程图

flowchart TD
    A["CreateResourceDownloaderByTags"] -->|传入tags数组| B["GetDownloadListByTags"]
    B -->|遍历| C["manifest.BundleList"]
    C -->|每个Bundle| D["GetBelongFileSystem"]
    D -->|检查| E["fileSystem.NeedDownload"]
    E -->|否| F["跳过该Bundle"]
    E -->|是| G["检查Bundle标签"]
    G -->|HasAnyTags = false| H["无标签Bundle
统一下载"]
    G -->|HasAnyTags = true| I["检查HasTag匹配"]
    I -->|匹配| J["DLC资源
添加到下载列表"]
    I -->|不匹配| K["跳过该Bundle"]
    H --> L["创建BundleInfo"]
    J --> L
    L --> M["添加到结果列表"]
    F --> N["继续下一个Bundle"]
    K --> N
    M --> N
    N -->|处理完成| O["返回下载列表"]
    O --> P["创建ResourceDownloaderOperation"]

    %% 样式定义
    style A fill:#ff6b6b,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#4ecdc4,stroke:#ffffff,stroke-width:2px,color:#000000
    style C fill:#45b7d1,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style D fill:#f9ca24,stroke:#ffffff,stroke-width:2px,color:#000000
    style E fill:#6c5ce7,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style F fill:#fd79a8,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style G fill:#00d2d3,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style H fill:#ff9ff3,stroke:#ffffff,stroke-width:2px,color:#000000
    style I fill:#00aaff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style J fill:#ff3838,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style K fill:#2ed573,stroke:#ffffff,stroke-width:2px,color:#000000
    style L fill:#ffa502,stroke:#ffffff,stroke-width:2px,color:#000000
    style M fill:#a29bfe,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style N fill:#74b9ff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style O fill:#e17055,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style P fill:#81ecec,stroke:#ffffff,stroke-width:2px,color:#000000

CreateResourceDownloaderByPaths

关键类

PlayModeImpl.cs
ResourceDownloaderOperation.cs
AssetInfo.cs
PackageManifest.cs

CreateResourceDownloaderByPaths 方法用于创建下载指定资源路径及其依赖的下载器，支持递归下载选项。

关键源代码

// PlayModeImpl.cs Line 122-127
ResourceDownloaderOperation IPlayMode.CreateResourceDownloaderByPaths(AssetInfo[] assetInfos, bool recursiveDownload, int downloadingMaxNumber, int failedTryAgain)
{
    List<BundleInfo> downloadList = GetDownloadListByPaths(ActiveManifest, assetInfos, recursiveDownload);
    var operation = new ResourceDownloaderOperation(PackageName, downloadList, downloadingMaxNumber, failedTryAgain);
    return operation;
}

// PlayModeImpl.cs Line 298-359 (核心逻辑)
public List<BundleInfo> GetDownloadListByPaths(PackageManifest manifest, AssetInfo[] assetInfos, bool recursiveDownload)
{
    if (manifest == null)
        return new List<BundleInfo>();

    // 获取资源对象的资源包和所有依赖资源包
    List<PackageBundle> checkList = new List<PackageBundle>();
    foreach (var assetInfo in assetInfos)
    {
        if (assetInfo.IsInvalid)
        {
            YooLogger.Warning(assetInfo.Error);
            continue;
        }

        // 获取主资源包
        PackageBundle mainBundle = manifest.GetMainPackageBundle(assetInfo.Asset);
        if (checkList.Contains(mainBundle) == false)
            checkList.Add(mainBundle);

        // 获取依赖资源包
        List<PackageBundle> mainDependBundles = manifest.GetAssetAllDependencies(assetInfo.Asset);
        foreach (var dependBundle in mainDependBundles)
        {
            if (checkList.Contains(dependBundle) == false)
                checkList.Add(dependBundle);
        }

        // 递归下载主资源包内所有资源对象依赖的资源包
        if (recursiveDownload)
        {
            foreach (var otherMainAsset in mainBundle.IncludeMainAssets)
            {
                var otherMainBundle = manifest.GetMainPackageBundle(otherMainAsset.BundleID);
                if (checkList.Contains(otherMainBundle) == false)
                    checkList.Add(otherMainBundle);

                List<PackageBundle> otherDependBundles = manifest.GetAssetAllDependencies(otherMainAsset);
                foreach (var dependBundle in otherDependBundles)
                {
                    if (checkList.Contains(dependBundle) == false)
                        checkList.Add(dependBundle);
                }
            }
        }
    }

    // 筛选需要下载的资源包
    List<BundleInfo> result = new List<BundleInfo>(1000);
    foreach (var packageBundle in checkList)
    {
        var fileSystem = GetBelongFileSystem(packageBundle);
        if (fileSystem == null)
            continue;

        if (fileSystem.NeedDownload(packageBundle))
        {
            var bundleInfo = new BundleInfo(fileSystem, packageBundle);
            result.Add(bundleInfo);
        }
    }
    return result;
}

流程图

flowchart TD
    A["CreateResourceDownloaderByPaths"] -->|AssetInfo数组| B["GetDownloadListByPaths"]
    B -->|遍历| C["AssetInfo数组"]
    C -->|每个AssetInfo| D{AssetInfo.IsInvalid?}
    D -->|是| E["记录警告
跳过该资源"]
    D -->|否| F["获取主资源包"]
    F --> G["添加到checkList"]
    G --> H["获取依赖资源包"]
    H --> I["添加依赖到checkList"]
    I --> J{recursiveDownload?}
    J -->|否| K["处理下一个AssetInfo"]
    J -->|是| L["递归处理主资源包内
所有资源的依赖"]
    L --> M["获取其他主资源包"]
    M --> N["获取其他依赖资源包"]
    N --> O["添加到checkList"]
    O --> K
    E --> K
    K -->|所有AssetInfo处理完| P["遍历checkList"]
    P -->|每个PackageBundle| Q["GetBelongFileSystem"]
    Q --> R{fileSystem.NeedDownload?}
    R -->|是| S["创建BundleInfo
添加到结果"]
    R -->|否| T["跳过该Bundle"]
    S --> U["继续下一个Bundle"]
    T --> U
    U -->|处理完成| V["返回下载列表"]
    V --> W["创建ResourceDownloaderOperation"]

    %% 样式定义
    style A fill:#ff6b6b,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#4ecdc4,stroke:#ffffff,stroke-width:2px,color:#000000
    style C fill:#45b7d1,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style D fill:#f9ca24,stroke:#ffffff,stroke-width:2px,color:#000000
    style E fill:#fd79a8,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style F fill:#6c5ce7,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style G fill:#a29bfe,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style H fill:#00d2d3,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style I fill:#ff9ff3,stroke:#ffffff,stroke-width:2px,color:#000000
    style J fill:#00aaff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style K fill:#ff3838,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style L fill:#2ed573,stroke:#ffffff,stroke-width:2px,color:#000000
    style M fill:#ffa502,stroke:#ffffff,stroke-width:2px,color:#000000
    style N fill:#74b9ff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style O fill:#e17055,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style P fill:#81ecec,stroke:#ffffff,stroke-width:2px,color:#000000
    style Q fill:#55a3ff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style R fill:#fd79a8,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style S fill:#00d2d3,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style T fill:#dda0dd,stroke:#ffffff,stroke-width:2px,color:#000000
    style U fill:#98fb98,stroke:#ffffff,stroke-width:2px,color:#000000
    style V fill:#ffd700,stroke:#ffffff,stroke-width:2px,color:#000000
    style W fill:#ff69b4,stroke:#ffffff,stroke-width:2px,color:#ffffff

下载器核心机制

ResourceDownloaderOperation 继承关系

flowchart LR
    AsyncOperationBase["AsyncOperationBase
异步操作基类"] 
    DownloaderOperation["DownloaderOperation
下载器操作基类"]
    ResourceDownloaderOperation["ResourceDownloaderOperation
资源下载器"]
    ResourceUnpackerOperation["ResourceUnpackerOperation
资源解压器"]
    ResourceImporterOperation["ResourceImporterOperation
资源导入器"]

    AsyncOperationBase -.->|继承| DownloaderOperation
    DownloaderOperation -.->|继承| ResourceDownloaderOperation
    DownloaderOperation -.->|继承| ResourceUnpackerOperation
    DownloaderOperation -.->|继承| ResourceImporterOperation

    %% 样式定义
    style AsyncOperationBase fill:#00aaff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style DownloaderOperation fill:#ff6600,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style ResourceDownloaderOperation fill:#00ff88,stroke:#ffffff,stroke-width:2px,color:#000000
    style ResourceUnpackerOperation fill:#ff4444,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style ResourceImporterOperation fill:#44ff44,stroke:#ffffff,stroke-width:2px,color:#000000

下载器状态机

flowchart TD
    A["DownloaderOperation.BeginDownload
外部使用"] -->|InternalStart| B["Check"]
    B -->|验证下载列表| C{下载列表有效?}
    C -->|无效| D["Done
Status=Failed"]
    C -->|有效| E["Loading"]
    E -->|创建下载器| F["动态管理下载器池"]
    F -->|检查下载结果| G{有失败的下载?}
    G -->|有| H["Done
Status=Failed"]
    G -->|无| I{所有下载完成?}
    I -->|否| J["继续下载"]
    I -->|是| K["Done
Status=Succeed"]
    J --> F

    %% 样式定义
    style A fill:#ff6b6b,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style B fill:#4ecdc4,stroke:#ffffff,stroke-width:2px,color:#000000
    style C fill:#f9ca24,stroke:#ffffff,stroke-width:2px,color:#000000
    style D fill:#fd79a8,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style E fill:#6c5ce7,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style F fill:#a29bfe,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style G fill:#00d2d3,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style H fill:#ff9ff3,stroke:#ffffff,stroke-width:2px,color:#000000
    style I fill:#00aaff,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style J fill:#ff3838,stroke:#ffffff,stroke-width:2px,color:#ffffff
    style K fill:#2ed573,stroke:#ffffff,stroke-width:2px,color:#000000

下载器池管理机制

DownloaderOperation 采用动态下载器池来优化下载性能，主要特性：

最大并发限制：通过 MAX_LOADER_COUNT = 64 和 _downloadingMaxNumber 控制同时下载的文件数量
失败重试机制：支持 _failedTryAgain 参数控制失败重试次数
动态调度：当有下载器完成时，自动从待下载列表中选择新的文件开始下载
暂停/恢复：支持 PauseDownload() 和 ResumeDownload() 控制下载状态
进度回调：提供详细的下载进度、错误、开始等事件回调

需要注意 DownloaderOperation.InternalUpdate 方法中的关键逻辑：

// 动态创建新的下载器到最大数量限制
// 注意：如果期间有下载失败的文件，暂停动态创建下载器
if (_bundleInfoList.Count > 0 && _failedList.Count == 0)
{
    if (_isPause)
        return;

    if (_downloaders.Count < _downloadingMaxNumber)
    {
        int index = _bundleInfoList.Count - 1;
        var bundleInfo = _bundleInfoList[index];
        var downloader = bundleInfo.CreateDownloader(_failedTryAgain);
        downloader.StartOperation();
        this.AddChildOperation(downloader);

        _downloaders.Add(downloader);
        _bundleInfoList.RemoveAt(index);
    }
}

从用户调用到UnityWebRequest的完整调用链

看完上面的分析，我觉得还需要把整个调用链梳理清楚，这样更容易理解整个下载流程。

调用链概述

用户调用下载器到最终发起UnityWebRequest的完整调用链是这样的：

graph TD
    A[用户代码] -->|downloader.BeginDownload| B[DownloaderOperation]
    B -->|OperationSystem.Update| C[InternalUpdate循环]
    C -->|bundleInfo.CreateDownloader| D[BundleInfo]
    D -->|_fileSystem.DownloadFileAsync| E[DefaultCacheFileSystem]
    E -->|new DownloadPackageBundleOperation| F[DownloadPackageBundleOperation]
    F -->|DownloadCenter.DownloadFileAsync| G[DownloadCenterOperation]
    G -->|创建具体下载器| H[UnityDownloadFileOperation]
    H -->|CreateWebRequest| I[UnityWebFileRequestOperation]
    I -->|_webRequest.SendWebRequest| J[UnityWebRequest]
    
    %% 详细步骤说明
    K[关键步骤说明]
    K --> L[用户调用BeginDownload启动下载]
    K --> M[OperationSystem每帧Update驱动]
    K --> N[BundleInfo适配不同FileSystem]
    K --> O[FileSystem创建具体下载操作]
    K --> P[DownloadCenter管理并发控制]
    K --> Q[UnityWebRequest执行实际网络请求]

    %% 暗色主题样式
    style A fill:#ff6b6b,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style B fill:#4ecdc4,stroke:#ffffff,stroke-width:3px,color:#000000
    style C fill:#45b7d1,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style D fill:#f9ca24,stroke:#ffffff,stroke-width:3px,color:#000000
    style E fill:#6c5ce7,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style F fill:#a29bfe,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style G fill:#fd79a8,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style H fill:#00d2d3,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style I fill:#ff9ff3,stroke:#ffffff,stroke-width:3px,color:#000000
    style J fill:#00aaff,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style K fill:#2ed573,stroke:#ffffff,stroke-width:3px,color:#000000
    style L fill:#ffa502,stroke:#ffffff,stroke-width:3px,color:#000000
    style M fill:#74b9ff,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style N fill:#e17055,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style O fill:#81ecec,stroke:#ffffff,stroke-width:3px,color:#000000
    style P fill:#55a3ff,stroke:#ffffff,stroke-width:3px,color:#ffffff
    style Q fill:#dda0dd,stroke:#ffffff,stroke-width:3px,color:#000000

关键调用点解析

1. 责任分离设计

DownloaderOperation：管理下载器池和并发控制
BundleInfo：适配器，统一不同FileSystem的接口
DefaultCacheFileSystem：处理URL获取和参数配置
DownloadPackageBundleOperation：状态机管理，重试逻辑
DownloadCenter：并发限制和下载器复用
UnityDownloadFileOperation：Unity网络请求的具体实现

2. 异步调用链

整个调用链是异步的，通过 OperationSystem 的 Update 循环驱动：

1 2	`// 主要更新循环 YooAsset.Update() → OperationSystem.Update() → AsyncOperationBase.Update() → InternalUpdate()`

3. 错误处理和重试

在调用链的每一层都有相应的错误处理：

DownloaderOperation：失败隔离策略
DownloadPackageBundleOperation：重试逻辑和超时处理
UnityWebRequest：网络层错误处理

Unity

#YooAssets

YooAsset源码阅读-Download

https://lshgame.com/2025/08/25/YooAsset_Code_Reading_Download/

作者

SuHang

发布于

2025年8月25日

许可协议

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