前言

此文章适合不太了解资源加载的萌新，有了入门基础之后再去github上搜大牛写的专业的资源加载方案才能得心应手，不然的话会看的很吃力或者说一脸懵逼。Unity里面关于资源加载我们都知道是下载更新AssetBundle，关于AssetBundle我之前的文章已经详细介绍过，没看过的朋友可以在看一下。下面介绍的资源加载的Demo有以下几点：
1.WWW下载图片资源
2.HTTP下载apk文件，并且支持断点续传，并且显示加载进度条
3.HTTP多线程下载文件

部分核心代码和讲解

WWW下载

思路：

WWW是Unity给我们封装的一个基于HTTP的简单类库，如果我们做很简单的下载，或者网络请求可以用这个类库，个人觉得这个封装的并不是很好，所以一般商业项目开发都不会使用这个，宁可自己去封装一个HTTP请求和下载的类库，可控性更好。仅仅是个人观点，不喜勿喷。

代码:

using UnityEngine;
using System.Collections;
using System;
using System.IO;

public class WWWLoad
{
    private WWW www = null;
    static System.Diagnostics.Stopwatch stopWatch = new System.Diagnostics.Stopwatch();
    /// <summary>
    /// 下载文件
    /// </summary>
    public IEnumerator DownFile(string url, string savePath, Action<WWW> process)
    {
        FileInfo file = new FileInfo(savePath);
        stopWatch.Start();
        UnityEngine.Debug.Log("Start:" + Time.realtimeSinceStartup);
        www = new WWW(url);
        while (!www.isDone)
        {
            yield return 0;
            if (process != null)
                process(www);
        }
        yield return www;
        if (www.isDone)
        {
            byte[] bytes = www.bytes;
            CreatFile(savePath, bytes);
        }
    }

    /// <summary>
    /// 创建文件
    /// </summary>
    /// <param name="bytes"></param>
    public void CreatFile(string savePath, byte[] bytes)
    {
        FileStream fs = new FileStream(savePath, FileMode.Append);
        BinaryWriter bw = new BinaryWriter(fs);
        fs.Write(bytes, 0, bytes.Length);
        fs.Flush();     //流会缓冲，此行代码指示流不要缓冲数据，立即写入到文件。
        fs.Close();     //关闭流并释放所有资源，同时将缓冲区的没有写入的数据，写入然后再关闭。
        fs.Dispose();   //释放流
        www.Dispose();

        stopWatch.Stop();
        Debug.Log("下载完成,耗时:" + stopWatch.ElapsedMilliseconds);
        UnityEngine.Debug.Log("End:" + Time.realtimeSinceStartup);
    }

}

HTTP下载并加载AB资源

思路：

主要用的核心类是HttpWebRequest，用这个类创建的对象可以申请下载的文件的大小以及下载的进度。移动上可读写的目录是PersidentDataPath，并且各个移动设备的路径不同，这点要注意，所以我们下载的AB资源就会下载到这个目录。

效果图：

核心代码：

using UnityEngine;
using System.Collections;
using System.Threading;
using System.IO;
using System.Net;
using System;

/// <summary>
/// 通过http下载资源
/// </summary>
public class HttpDownLoad {
    //下载进度
    public float progress{get; private set;}
    //涉及子线程要注意,Unity关闭的时候子线程不会关闭，所以要有一个标识
    private bool isStop;
    //子线程负责下载，否则会阻塞主线程，Unity界面会卡主
    private Thread thread;
    //表示下载是否完成
    public bool isDone{get; private set;}
    const int ReadWriteTimeOut = 2 * 1000;//超时等待时间
    const int TimeOutWait = 5 * 1000;//超时等待时间


    /// <summary>
    /// 下载方法(断点续传)
    /// </summary>
    /// <param name="url">URL下载地址</param>
    /// <param name="savePath">Save path保存路径</param>
    /// <param name="callBack">Call back回调函数</param>
    public void DownLoad(string url, string savePath,string fileName, Action callBack, System.Threading.ThreadPriority threadPriority = System.Threading.ThreadPriority.Normal)
    {
        isStop = false;
        System.Diagnostics.Stopwatch stopWatch = new System.Diagnostics.Stopwatch();
        //开启子线程下载,使用匿名方法
        thread = new Thread(delegate() {
            stopWatch.Start();
            //判断保存路径是否存在
            if (!Directory.Exists(savePath))
            {
                Directory.CreateDirectory(savePath);
            }
            //这是要下载的文件名，比如从服务器下载a.zip到D盘，保存的文件名是test
            string filePath = savePath + "/"+ fileName;

            //使用流操作文件
            FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate, FileAccess.Write);
            //获取文件现在的长度
            long fileLength = fs.Length;
            //获取下载文件的总长度
            UnityEngine.Debug.Log(url+" "+fileName);
            long totalLength = GetLength(url);
            Debug.LogFormat("<color=red>文件:{0} 已下载{1}M，剩余{2}M</color>",fileName,fileLength/1024/1024,(totalLength- fileLength)/ 1024/1024);         

            //如果没下载完
            if(fileLength < totalLength)
            {

                //断点续传核心，设置本地文件流的起始位置
                fs.Seek(fileLength, SeekOrigin.Begin);

                HttpWebRequest request = HttpWebRequest.Create(url) as HttpWebRequest;

                request.ReadWriteTimeout = ReadWriteTimeOut;
                request.Timeout = TimeOutWait;

                //断点续传核心，设置远程访问文件流的起始位置
                request.AddRange((int)fileLength);

                Stream  stream = request.GetResponse().GetResponseStream();
                byte[] buffer = new byte[1024];
                //使用流读取内容到buffer中
                //注意方法返回值代表读取的实际长度,并不是buffer有多大，stream就会读进去多少
                int length = stream.Read(buffer, 0, buffer.Length);
                //Debug.LogFormat("<color=red>length:{0}</color>" + length);
                while (length > 0)
                {
                    //如果Unity客户端关闭，停止下载
                    if(isStop) break;
                    //将内容再写入本地文件中
                    fs.Write(buffer, 0, length);
                    //计算进度
                    fileLength += length;
                    progress = (float)fileLength / (float)totalLength;
                    //UnityEngine.Debug.Log(progress);
                    //类似尾递归
                    length = stream.Read(buffer, 0, buffer.Length);

                }
                stream.Close();
                stream.Dispose();

            }
            else
            {
                progress = 1;
            }
            stopWatch.Stop();
            Debug.Log("耗时: " + stopWatch.ElapsedMilliseconds);
            fs.Close();
            fs.Dispose();
            //如果下载完毕，执行回调
            if(progress == 1)
            {
                isDone = true;
                if (callBack != null) callBack();
                thread.Abort();
            }
            UnityEngine.Debug.Log ("download finished");    
        });
        //开启子线程
        thread.IsBackground = true;
        thread.Priority = threadPriority;
        thread.Start();
    }


    /// <summary>
    /// 获取下载文件的大小
    /// </summary>
    /// <returns>The length.</returns>
    /// <param name="url">URL.</param>
    long GetLength(string url)
    {
        UnityEngine.Debug.Log(url);

        HttpWebRequest requet = HttpWebRequest.Create(url) as HttpWebRequest;
        requet.Method = "HEAD";
        HttpWebResponse response = requet.GetResponse() as HttpWebResponse;
        return response.ContentLength;
    }

    public void Close()
    {
        isStop = true;
    }

}

多线程下载文件

思路：

多线程下载思路是计算一个文件包大小，然后创建几个线程，计算每一个线程下载的始末下载的位置，最后是合并成一个整体的文件包写入到本地。

效果图：

核心代码：

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Net;
using UnityEngine;
using System.Threading;

public class MultiHttpDownLoad : MonoBehaviour
{
    string savePath = string.Empty;
    string FileName = "ClickEffect.apk";
    //string resourceURL = @"http://www.aladdingame.online/wuzhang/Resources/ClickEffect.apk";// @"http://www.dingxiaowei.cn/birdlogo.png";
    string resourceURL = @"http://www.dingxiaowei.cn/ClickEffect.apk";
    string saveFile = string.Empty;
    public int ThreadNum { get; set; }
    public bool[] ThreadStatus { get; set; }
    public string[] FileNames { get; set; }
    public int[] StartPos { get; set; }
    public int[] FileSize { get; set; }
    public string Url { get; set; }
    public bool IsMerge { get; set; }
    private int buffSize = 1024;
    DateTime beginTime;

    void Start()
    {
#if UNITY_EDITOR || UNITY_STANDALONE_WIN
        savePath = Application.streamingAssetsPath;
#elif UNITY_ANDROID
          savePath = Application.persistentDataPath;;
#endif
        saveFile = Path.Combine(savePath, FileName);

        DownDoad();
    }

    void Init(long fileSize)
    {
        if (ThreadNum == 0)
            ThreadNum = 5;

        ThreadStatus = new bool[ThreadNum];
        FileNames = new string[ThreadNum];
        StartPos = new int[ThreadNum];//下载字节起始点
        FileSize = new int[ThreadNum];//该进程文件大小
        int fileThread = (int)fileSize / ThreadNum;//单进程文件大小
        int fileThreade = fileThread + (int)fileSize % ThreadNum;//最后一个进程的资源大小
        for (int i = 0; i < ThreadNum; i++)
        {
            ThreadStatus[i] = false;
            FileNames[i] = i.ToString() + ".dat";
            if (i < ThreadNum - 1)
            {
                StartPos[i] = fileThread * i;
                FileSize[i] = fileThread;
            }
            else
            {
                StartPos[i] = fileThread * i;
                FileSize[i] = fileThreade;
            }
        }
    }

    void DownDoad()
    {
        UnityEngine.Debug.Log("开始下载 时间:" + System.DateTime.Now.ToString());
        beginTime = System.DateTime.Now;
        Url = resourceURL;
        long fileSizeAll = 0;
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
        fileSizeAll = request.GetResponse().ContentLength;
        Init(fileSizeAll);

        System.Threading.Thread[] threads = new System.Threading.Thread[ThreadNum];
        HttpMultiThreadDownload[] httpDownloads = new HttpMultiThreadDownload[ThreadNum];
        for (int i = 0; i < ThreadNum; i++)
        {
            httpDownloads[i] = new HttpMultiThreadDownload(request, this, i);
            threads[i] = new System.Threading.Thread(new System.Threading.ThreadStart(httpDownloads[i].Receive));
            threads[i].Name = string.Format("线程{0}:", i);
            threads[i].Start();
        }
        StartCoroutine(MergeFile());
    }

    IEnumerator MergeFile()
    {
        while (true)
        {
            IsMerge = true;
            for (int i = 0; i < ThreadNum; i++)
            {
                if (ThreadStatus[i] == false)
                {
                    IsMerge = false;
                    yield return 0;
                    System.Threading.Thread.Sleep(100);
                    break;
                }
            }
            if (IsMerge)
                break;
        }

        int bufferSize = 512;
        string downFileNamePath = saveFile;
        byte[] bytes = new byte[bufferSize];
        FileStream fs = new FileStream(downFileNamePath, FileMode.Create);
        FileStream fsTemp = null;

        for (int i = 0; i < ThreadNum; i++)
        {
            fsTemp = new FileStream(FileNames[i], FileMode.Open);
            while (true)
            {
                yield return 0;
                buffSize = fsTemp.Read(bytes, 0, bufferSize);
                if (buffSize > 0)
                    fs.Write(bytes, 0, buffSize);
                else
                    break;
            }
            fsTemp.Close();
        }
        fs.Close();
        Debug.Log("接受完毕!!!结束时间:" + System.DateTime.Now.ToString());
        Debug.LogError("下载耗时:" + (System.DateTime.Now - beginTime).TotalSeconds.ToString());
        yield return null;
        DeleteCacheFiles();
    }

    private void DeleteCacheFiles()
    {
        for (int i = 0; i < ThreadNum; i++)
        {
            FileInfo info = new FileInfo(FileNames[i]);
            Debug.LogFormat("Delete File {0} OK!", FileNames[i]);
            info.Delete();
        }
    }
}

public class HttpMultiThreadDownload
{
    private int threadId;
    private string url;
    MultiHttpDownLoad downLoadObj;
    private const int buffSize = 1024;
    HttpWebRequest request;

    public HttpMultiThreadDownload(HttpWebRequest request, MultiHttpDownLoad downLoadObj, int threadId)
    {
        this.request = request;
        this.threadId = threadId;
        this.url = downLoadObj.Url;
        this.downLoadObj = downLoadObj;
    }

    public void Receive()
    {
        string fileName = downLoadObj.FileNames[threadId];
        var buffer = new byte[buffSize];
        int readSize = 0;
        FileStream fs = new FileStream(fileName, System.IO.FileMode.Create);
        Stream ns = null;

        try
        {
            request.AddRange(downLoadObj.StartPos[threadId], downLoadObj.StartPos[threadId] + downLoadObj.FileSize[threadId]);
            ns = request.GetResponse().GetResponseStream();
            readSize = ns.Read(buffer, 0, buffSize);
            showLog("线程[" + threadId.ToString() + "] 正在接收 " + readSize);
            while (readSize > 0)
            {
                fs.Write(buffer, 0, readSize);
                readSize = ns.Read(buffer, 0, buffSize);
                showLog("线程[" + threadId.ToString() + "] 正在接收 " + readSize);
            }
            fs.Close();
            ns.Close();
        }
        catch (Exception er)
        {
            Debug.LogError(er.Message);
            fs.Close();
        }
        showLog("线程[" + threadId.ToString() + "] 结束!");
        downLoadObj.ThreadStatus[threadId] = true;
    }

    private void showLog(string processing)
    {
        Debug.Log(processing);
    }
}

线程下载速度跟线程的关系呈钟罩式关系，也就是说适量的线程数量会提高下载速度，但并不是说线程数越多就越好，因为线程的切换和资源的整合也是需要时间的。下面就列举下载单个文件，创建的线程数和对应的下载时间：

• 单线程
  
• 5个线程
  
• 15个线程
  

这里我是1M的带宽，下载的是一个300KB左右的资源，一般不会做多线程下载单一资源，多线程下载一般用于下载多个资源，除非单一资源真的很大才有多线程下载，然后做合包操作。

Demo下载

http://git.oschina.net/dingxiaowei/UnityResourceDownload
关注后续更新请点start或者fork，感谢！

开发交流

1群

1群如果已经满员，请加2群
159875734

后续计划

写一个实际商业项目中用到的资源更新案例。