描述

对于一个网络游戏来说，下载网络上面的文件一定是必不可少的一个功能，例如更新资源包。在Unity中，我们可以用系统的WWW或者HttpWebRequest来实现文件的下载。其中有些较大的文件下载需要断点续传的功能（即下载了一部分突然中断下载后，再次下载直接从上次下载的地方继续下载，而不是重新下载），需要使用HttpWebRequest。

这一篇我们主要就讲一讲这两种下载方式的实现（主要都是代码）。

基类

首先先创建一个基类，里面存放下载需要的一些数据，例如文件url，下载存放路径等等。

public abstract class DownloadItem {/// <summary>/// 网络资源url路径/// </summary>protected string m_srcUrl;/// <summary>/// 资源下载存放路径，不包含文件名/// </summary>protected string m_savePath;/// <summary>/// 文件名,不包含后缀/// </summary>protected string m_fileNameWithoutExt;/// <summary>/// 文件后缀/// </summary>protected string m_fileExt;/// <summary>/// 下载文件全路径，路径+文件名+后缀/// </summary>protected string m_saveFilePath;/// <summary>/// 原文件大小/// </summary>protected long m_fileLength;/// <summary>/// 当前下载好了的大小/// </summary>protected long m_currentLength;/// <summary>/// 是否开始下载/// </summary>protected bool m_isStartDownload;public bool isStartDownload {get {return m_isStartDownload;}}public DownloadItem(string url, string path) {m_srcUrl = url;m_savePath = path;m_isStartDownload = false;m_fileNameWithoutExt = Path.GetFileNameWithoutExtension(m_srcUrl);m_fileExt = Path.GetExtension(m_srcUrl);m_saveFilePath = string.Format("{0}/{1}{2}", m_savePath, m_fileNameWithoutExt, m_fileExt);}/// <summary>/// 开始下载/// </summary>/// <param name="callback">下载完成回调</param>public virtual void StartDownload(Action callback = null) {if(string.IsNullOrEmpty(m_srcUrl) || string.IsNullOrEmpty(m_savePath)) {return;}//若存放目录不存在则创建目录FileTool.CreateDirectory(m_saveFilePath);}/// <summary>/// 获取下载进度/// </summary>/// <returns>进度，0-1</returns>public abstract float GetProcess();/// <summary>/// 获取当前下载了的文件大小/// </summary>/// <returns>当前文件大小</returns>public abstract long GetCurrentLength();/// <summary>/// 获取要下载的文件大小/// </summary>/// <returns>文件大小</returns>public abstract long GetLength();public abstract void Destroy();
}

WWW

www的方式下载很简单，等www读取好后，直接使用www.bytes去生成文件即可。这种方式文件是一次性生成的，适合小资源的下载

/// <summary>
/// WWW的方式下载
/// </summary>
public class WWWDownloadItem : DownloadItem {WWW m_www;public WWWDownloadItem(string url, string path) : base(url, path) {}public override void StartDownload(Action callback = null) {base.StartDownload();UICoroutine.instance.StartCoroutine(Download(callback));}IEnumerator Download(Action callback = null) {m_www = new WWW(m_srcUrl);m_isStartDownload = true;yield return m_www;//WWW读取完成后，才开始往下执行m_isStartDownload = false;if(m_www.isDone) {byte[] bytes = m_www.bytes;//创建文件FileTool.CreatFile(m_saveFilePath, bytes);} else {Debug.Log("Download Error:" + m_www.error);}if(callback != null) {callback();}}public override float GetProcess() {if(m_www != null) {return m_www.progress;}return 0;}public override long GetCurrentLength() {if(m_www != null) {return m_www.bytesDownloaded;}return 0;}public override long GetLength() {return 0;}public override void Destroy() {if(m_www != null) {m_www.Dispose();m_www = null;}}
}

HTTP

这种方式下载，我们采用的是边读取边生成对应文件，适合较大文件下载。关于断点续传的处理，我们下载的时候，先根据读取的内容生成一个临时文件，当全部下载好后，才将这个临时文件转换成正式的文件名。若中途下载中断，已下载好的那部分文件依据在对应目录下，我们下次下载可以直接在上次下载的临时文件后添加内容。

所以下载逻辑就是，每次下载先判断是否有对应的临时文件，若没有则是第一次下载，从初始位置读取下载，若有该文件，则读取该文件信息，获取文件大小当之后的读取下载的偏移量，从当前位置开始下载，直至下载完成。

/// <summary>
/// HTTP的方式下载，支持断点续传
/// </summary>
public class HttpDownloadItem : DownloadItem {/// <summary>/// 临时文件后缀名/// </summary>string m_tempFileExt = ".temp";/// <summary>/// 临时文件全路径/// </summary>string m_tempSaveFilePath;public HttpDownloadItem(string url, string path) : base(url, path) {m_tempSaveFilePath = string.Format("{0}/{1}{2}", m_savePath, m_fileNameWithoutExt, m_tempFileExt);}public override void StartDownload(Action callback = null) {base.StartDownload();UICoroutine.instance.StartCoroutine(Download(callback));}IEnumerator Download(Action callback = null) {HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(m_srcUrl);request.Method = "GET";FileStream fileStream;if(File.Exists(m_tempSaveFilePath)) {//若之前已下载了一部分，继续下载fileStream = File.OpenWrite(m_tempSaveFilePath);m_currentLength = fileStream.Length;fileStream.Seek(m_currentLength, SeekOrigin.Current);//设置下载的文件读取的起始位置request.AddRange((int)m_currentLength);} else {//第一次下载fileStream = new FileStream(m_tempSaveFilePath, FileMode.Create, FileAccess.Write);m_currentLength = 0;}HttpWebResponse response = (HttpWebResponse)request.GetResponse();Stream stream = response.GetResponseStream();//总的文件大小=当前需要下载的+已下载的m_fileLength = response.ContentLength + m_currentLength;m_isStartDownload = true;int lengthOnce;int bufferMaxLength = 1024 * 20;while(m_currentLength < m_fileLength) {byte[] buffer = new byte[bufferMaxLength];if(stream.CanRead) {//读写操作lengthOnce = stream.Read(buffer, 0, buffer.Length);m_currentLength += lengthOnce;fileStream.Write(buffer, 0, lengthOnce);} else {break;}yield return null;}m_isStartDownload = false;response.Close();stream.Close();fileStream.Close();//临时文件转为最终的下载文件File.Move(m_tempSaveFilePath, m_saveFilePath);if(callback != null) {callback();}}public override float GetProcess() {if(m_fileLength > 0) {return Mathf.Clamp((float)m_currentLength / m_fileLength, 0, 1);}return 0;}public override long GetCurrentLength() {return m_currentLength;}public override long GetLength() {return m_fileLength;}public override void Destroy() {}
}

补充

上述代码用到了两个自定义的方法FileTool.CreateDirectory()和FileTool.CreatFile()，内容很简单，如下

public class FileTool {/// <summary>/// 创建目录/// </summary>/// <param name="filePath">需要创建的目录路径</param>public static void CreateDirectory(string filePath) {if(!string.IsNullOrEmpty(filePath)) {string dirName = Path.GetDirectoryName(filePath);if(!Directory.Exists(dirName)) {Directory.CreateDirectory(dirName);}}}/// <summary>/// 创建文件/// </summary>/// <param name="filePath">文件路径</param>/// <param name="bytes">文件内容</param>public static void CreatFile(string filePath, byte[] bytes) {FileInfo file = new FileInfo(filePath);Stream stream = file.Create();stream.Write(bytes, 0, bytes.Length);stream.Close();stream.Dispose();}
}

使用

public class DownloadDemo : MonoBehaviour {DownloadItem m_item;string testScrUrl = "http://dlsw.baidu.com/sw-search-sp/soft/ca/13442/Thunder_dl_7.9.42.5050.1449557123.exe";int count = 0;void Start() {Debug.Log(Application.persistentDataPath);//m_item = new WWWDownloadItem(testScrUrl, Application.persistentDataPath);//m_item.StartDownload(DownloadFinish);m_item = new HttpDownloadItem(testScrUrl, Application.persistentDataPath);m_item.StartDownload(DownloadFinish);}void Update() {count++;if(count % 20 == 0) {if(m_item != null && m_item.isStartDownload) {Debug.Log("下载进度------" + m_item.GetProcess() + "------已下载大小---" + m_item.GetCurrentLength());}}}void DownloadFinish() {Debug.Log("DownloadFinish！！！");}
}

补充：由于个人失误，忘记添加了UICoroutine相关的代码，深表歉意。UICoroutine在这个例子中的作用其实就是场景中新建一个GameObject，专门用来启用协程，因为前面的几个类没有继承于MonoBehaviour，所以无法直接调用StartCoroutine方法

public class UICoroutine : MonoBehaviour {private static UICoroutine mInstance = null;public static UICoroutine uiCoroutine {get {if(mInstance == null) {GameObject go = new GameObject();if(go != null) {go.name = "_UICoroutine";go.AddComponent<UICoroutine>();} else {Debug.LogError("Init UICoroutine faild. GameObjet can not be null.");}}return mInstance;}}void Awake() {DontDestroyOnLoad(gameObject);mInstance = this;}void OnDestroy() {mInstance = null;}
}