下载大文件

Question

通过下载文件UnityEngine.WWW,我收到错误

OverflowException:Number溢出.

我发现错误是由结构本身引起的,因为字节数组比int.MaxValue可以分配更多的字节(~2GB).

通过返回数组来触发错误www.bytes,这意味着框架可能以其他方式存储数组.

如何以其他方式访问下载的数据,还是有更大的文件替代？

public IEnumerator downloadFile()
{
    WWW www = new WWW(filesource);

    while(!www.isDone)
    {
        progress = www.progress;
        yield return null;
    }

    if(string.IsNullOrEmpty(www.error))
    {
        data = www.bytes; // <- Errormessage fired here
    }
}

Answer 1

新答案(Unity 2017.2及以上版本)

使用UnityWebRequest带DownloadHandlerFile.该DownloadHandlerFile班是新的,用于直接下载和保存文件,同时防止高内存使用情况.

IEnumerator Start()
{
    string url = "http://dl3.webmfiles.org/big-buck-bunny_trailer.webm";

    string vidSavePath = Path.Combine(Application.persistentDataPath, "Videos");
    vidSavePath = Path.Combine(vidSavePath, "MyVideo.webm");

    //Create Directory if it does not exist
    if (!Directory.Exists(Path.GetDirectoryName(vidSavePath)))
    {
        Directory.CreateDirectory(Path.GetDirectoryName(vidSavePath));
    }

    var uwr = new UnityWebRequest(url);
    uwr.method = UnityWebRequest.kHttpVerbGET;
    var dh = new DownloadHandlerFile(vidSavePath);
    dh.removeFileOnAbort = true;
    uwr.downloadHandler = dh;
    yield return uwr.SendWebRequest();

    if (uwr.isNetworkError || uwr.isHttpError)
        Debug.Log(uwr.error);
    else
        Debug.Log("Download saved to: " + vidSavePath.Replace("/", "\\") + "\r\n" + uwr.error);
}

旧答案(Unity 2017.1及以下版本)如果要在下载文件时访问每个字节,请使用此选项)

像这样的问题是为什么Unity UnityWebRequest已经制作但它不能直接工作,因为WWWAPI现在UnityWebRequest在最新版本的Unity 中的API 之上实现,这意味着如果你得到WWWAPI的错误,你也可能会得到相同的错误UnityWebRequest.即使它有效,你也可能在像Android这样的小型内存移动设备上遇到问题.

该怎么做是使用UnityWebRequest的DownloadHandlerScript功能,它允许您以块的形式下载数据.通过以块的形式下载数据,可以防止导致溢出错误.该WWWAPI没有实现这个功能,因此UnityWebRequest并DownloadHandlerScript必须用于下载数据块中的数据.你可以在这里阅读它是如何工作的.

虽然这应该可以解决您当前的问题,但在尝试保存大数据时可能会遇到另一个内存问题File.WriteAllBytes.用FileStream做储蓄的部分,并关闭它,只有当下载完成.

创建UnityWebRequest用于以块的形式下载数据的自定义,如下所示:

using System;
using System.IO;
using UnityEngine;
using UnityEngine.Networking;

public class CustomWebRequest : DownloadHandlerScript
{
    // Standard scripted download handler - will allocate memory on each ReceiveData callback
    public CustomWebRequest()
        : base()
    {
    }

    // Pre-allocated scripted download handler
    // Will reuse the supplied byte array to deliver data.
    // Eliminates memory allocation.
    public CustomWebRequest(byte[] buffer)
        : base(buffer)
    {

        Init();
    }

    // Required by DownloadHandler base class. Called when you address the 'bytes' property.
    protected override byte[] GetData() { return null; }

    // Called once per frame when data has been received from the network.
    protected override bool ReceiveData(byte[] byteFromServer, int dataLength)
    {
        if (byteFromServer == null || byteFromServer.Length < 1)
        {
            Debug.Log("CustomWebRequest :: ReceiveData - received a null/empty buffer");
            return false;
        }

        //Write the current data chunk to file
        AppendFile(byteFromServer, dataLength);

        return true;
    }

    //Where to save the video file
    string vidSavePath;
    //The FileStream to save the file
    FileStream fileStream = null;
    //Used to determine if there was an error while opening or saving the file
    bool success;

    void Init()
    {
        vidSavePath = Path.Combine(Application.persistentDataPath, "Videos");
        vidSavePath = Path.Combine(vidSavePath, "MyVideo.webm");


        //Create Directory if it does not exist
        if (!Directory.Exists(Path.GetDirectoryName(vidSavePath)))
        {
            Directory.CreateDirectory(Path.GetDirectoryName(vidSavePath));
        }


        try
        {
            //Open the current file to write to
            fileStream = new FileStream(vidSavePath, FileMode.OpenOrCreate, FileAccess.ReadWrite);
            Debug.Log("File Successfully opened at" + vidSavePath.Replace("/", "\\"));
            success = true;
        }
        catch (Exception e)
        {
            success = false;
            Debug.LogError("Failed to Open File at Dir: " + vidSavePath.Replace("/", "\\") + "\r\n" + e.Message);
        }
    }

    void AppendFile(byte[] buffer, int length)
    {
        if (success)
        {
            try
            {
                //Write the current data to the file
                fileStream.Write(buffer, 0, length);
                Debug.Log("Written data chunk to: " + vidSavePath.Replace("/", "\\"));
            }
            catch (Exception e)
            {
                success = false;
            }
        }
    }

    // Called when all data has been received from the server and delivered via ReceiveData
    protected override void CompleteContent()
    {
        if (success)
            Debug.Log("Done! Saved File to: " + vidSavePath.Replace("/", "\\"));
        else
            Debug.LogError("Failed to Save File to: " + vidSavePath.Replace("/", "\\"));

        //Close filestream
        fileStream.Close();
    }

    // Called when a Content-Length header is received from the server.
    protected override void ReceiveContentLength(int contentLength)
    {
        //Debug.Log(string.Format("CustomWebRequest :: ReceiveContentLength - length {0}", contentLength));
    }
}

如何使用:

UnityWebRequest webRequest;
//Pre-allocate memory so that this is not done each time data is received
byte[] bytes = new byte[2000];

IEnumerator Start()
{
    string url = "http://dl3.webmfiles.org/big-buck-bunny_trailer.webm";
    webRequest = new UnityWebRequest(url);
    webRequest.downloadHandler = new CustomWebRequest(bytes);
    webRequest.SendWebRequest();
    yield return webRequest;
}