【Unity开发】避免重复加载场景资产AB(AssetBundle)包的优化

@[TOC](【Unity开发】避免重复加载场景资产AB(AssetBundle)包的优化）

Unity2022，项目需要远程加载场景AB包，并加载场景。

1、 初始方案

1.1 异步加载场景资产（获取AB包数据）

	// 异步加载远程资产（获取远程AB包数据）
	public IEnumerator LoadAssetFromAB(string url, Action<AssetBundle> assetAB)
    {
        yield return new WaitForSeconds(0.16f);
        using (UnityWebRequest webRequest = UnityWebRequestAssetBundle.GetAssetBundle(url))
        {
            yield return webRequest.SendWebRequest();
            if (webRequest.result == UnityWebRequest.Result.Success){
                    var bundle = DownloadHandlerAssetBundle.GetContent(webRequest);
                    assetAB?.Invoke(bundle);
            }
        }
    }

1.2 异步加载场景（进入场景）

	// 异步加载场景
    public void LoadSceneFromAB(string sceneName){
        // 启动异步线程加载场景
        StartCoroutine(AssetToScene(sceneName));
    }

    // 异步场景加载迭代器
    private IEnumerator AssetToScene(string sceneName){
        // 异步加载场景资产
        AsyncOperation  loadOperation = SceneManager.LoadSceneAsync(sceneName);
        yield return loadOperation;

        Debug.Log("应该到不了这里就直接转场了,那么AB资产包还在内存,下次就会报[重复加载]的异常");
        // 卸载内存中的assetAB资产(除了LoadScene创建出来的场景)
        assetAB.Unload(false);
    }

1.3 点击跳转场景

	public void GotoScene(ClickEvent evt){
            string sceneName = "myScene";
            char dsp = Path.AltDirectorySeparatorChar;
            string url = Application.dataPath + dsp + "scene" + dsp + sceneName;

            // 销毁所有未使用资产
            Resources.UnloadUnusedAssets();

            // 临时解决方案
            // 尝试直接加载AB场景 (避免AB资产已在内存时AB包重复报错)
            // The AssetBundle 'http://192.168.2.107:8080/level/Level1' can't be loaded because another AssetBundle with the same files is already loaded.
            SceneManager.LoadScene(sceneName);
            // 这里如果成功加载场景，不会走到下一步，
            // 前提是内存里有场景包 1、上次已经加载到内存没卸载 2、程序Build编译时Scenes In Build
            // Scene 'Level1' couldn't be loaded because it has not been added to the build settings or the AssetBundle has not been loaded.
			//To add a scene to the build settings use the menu File->Build Settings...

            // 远程异步加载AB场景资产
            StartCoroutine(_dataRestapi.LoadAssetFromAB(url, (assetAB) => {
                if (assetAB != null) {
                    LoadSceneFromAB(sceneName);
                }else{
                    Debug.LogWarning("场景资产数据加载失败");
                }
            }));
    }

2、 优化方案

2.1 异步加载场景资产（获取AB包数据）

2.1.1 实用精简版

	public IEnumerator LoadAssetFromAB(string url, Action<AssetBundle> assetAB)
    {
        yield return new WaitForSeconds(0.16f);
        using (UnityWebRequest webRequest = UnityWebRequestAssetBundle.GetAssetBundle(url))
        {
            // 等待通讯结束
            yield return webRequest.SendWebRequest();

            // 下载成功
            if (webRequest.result == UnityWebRequest.Result.Success){
                Debug.Log(string.Format("下载进度: {0}%", 100));
                var bundle = DownloadHandlerAssetBundle.GetContent(webRequest);
                assetAB?.Invoke(bundle);
            }
        }
    }

2.1.2 加载进度版本

    // 异步加载远程资产（获取远程AB包数据）
   	public IEnumerator LoadAssetFromAB(string url, Action<AssetBundle> assetAB)
    {
        yield return new WaitForSeconds(0.16f);
        using (UnityWebRequest webRequest = UnityWebRequestAssetBundle.GetAssetBundle(url))
        {
            // 服务器通讯
            webRequest.SendWebRequest();

            // 下载进度信息
            while (!webRequest.isDone)
            {
                float progress = webRequest.downloadProgress;
                Debug.Log(string.Format("下载进度: {0}%", (progress/0.9*100).ToString("F2")));
                yield return null;
            }

            // 下载成功
            if (webRequest.result == UnityWebRequest.Result.Success){
                Debug.Log(string.Format("下载进度: {0}%", 100));
                // 从下载缓存提取AB资产包格式数据
                var bundle = DownloadHandlerAssetBundle.GetContent(webRequest);
                assetAB?.Invoke(bundle);
            }
        }
    }

2.1.3 资产本地化版本

    // 异步远程资产本地化并加载（保存远程AB包数据到本地）
   	public IEnumerator SaveAssetFromAB(string url, Action<AssetBundle> assetAB)
    {
        yield return new WaitForSeconds(0.16f);
        using (UnityWebRequest webRequest = UnityWebRequestAssetBundle.GetAssetBundle(url))
        {
            // 将AB字节数据写入本地文件
            string locfile = url.Replace(remoteBundleURL, localBundlePath);
            var handler = new DownloadHandlerFile(locfile);
            webRequest.downloadHandler = handler;

            // 服务器通讯
            webRequest.SendWebRequest();

            // 下载进度信息
            while (!webRequest.isDone)
            {
                float progress = webRequest.downloadProgress;
                Debug.Log(string.Format("下载进度: {0}%", (progress*100).ToString("F2")));
                yield return null;
            }

            // 下载成功
            if (webRequest.result == UnityWebRequest.Result.Success){
                Debug.Log(string.Format("下载进度: {0}%", 100));

                // 从本地文件提取AB资产数据
                var bundle = AssetBundle.LoadFromFile(locfile);
                assetAB?.Invoke(bundle);
            }
        }
    }

2.2 异步加载场景（进入场景）

1 注册后处理事件 SceneManager.sceneLoaded += OnSceneLoaded;
2 删除永远不会被运行的 assetAB.Unload(false);

	// 异步加载场景
    public void LoadSceneFromAB(string sceneName){
        // 启动异步线程加载场景
        StartCoroutine(AssetToScene(sceneName));
        // 当新场景开始加载时注册事件 解决加载完成后处理事件
        SceneManager.sceneLoaded += OnSceneLoaded;
    }

    // 异步场景加载迭代器
    private IEnumerator AssetToScene(string sceneName){
        // 异步加载场景资产
        AsyncOperation  loadOperation = SceneManager.LoadSceneAsync(sceneName);
        yield return loadOperation;
    }

2.3 点击跳转场景

删除尝试加载场景 SceneManager.LoadScene(sceneName);
因为不需要了，每次运行都是从远程获取最新的场景AB包

	// 声明AB资产缓存用于后处理事件
	private AssetBundle _assetAB;
	// 场景加载触发事件
	public void GotoScene(string sceneName){
            char dsp = Path.AltDirectorySeparatorChar;
            string url = Application.dataPath + dsp + "scene" + dsp + sceneName;

            // 销毁所有未使用资产
            Resources.UnloadUnusedAssets();

            // 远程异步加载AB场景资产
            StartCoroutine(LoadAssetFromAB(url, (assetAB) => {
                if (assetAB != null) {
                    // 缓存资产用于后处理事件
                    _assetAB = assetAB;
                    // 异步加载场景（进入场景）
                    LoadSceneFromAB(sceneName);
                }else{
                    Debug.LogWarning("场景资产数据加载失败");
                }
            }));
    }

2.4 增加场景加载后处理事件

保证场景加载完成后自动删除场景AB资产包

	// 场景加载后处理事件
    void OnSceneLoaded(Scene scene, LoadSceneMode mode)
    {
        // 当新场景加载完成后，卸载内存中AssetBundle包(除了Load创建出来的对象/场景)
        _assetAB.Unload(false);

        // 注销事件，防止重复调用
        SceneManager.sceneLoaded -= OnSceneLoaded;
    }