等待直到通过webClient从URL下载文件 [英] Wait until file is downloaded from URL via webClient

问题描述

我很难从URL下载一些MB excel文件，然后使用它.我正在使用VS2010，所以我不能使用await关键字. 我的代码如下:

I have struggle with downloading few MB excel file from URL and then work with it. Im using VS2010 so i cant use await keyword. My code follows:

using (WebClient webClient = new WebClient())
                {
                    // setting Windows Authentication
                    webClient.UseDefaultCredentials = true;
                    // event fired ExcelToCsv after file is downloaded
                    webClient.DownloadFileCompleted += (sender, e) => ExcelToCsv(fileName);
                    // start download
                    webClient.DownloadFileAsync(new Uri("http://serverx/something/Export.ashx"), exportPath);
                }

ExcelToCsv()方法中的行

using (FileStream stream = new FileStream(filePath, FileMode.Open))

向我抛出错误:

System.IO.IOException:该进程无法访问文件，因为它 正在被另一个进程使用.

System.IO.IOException: The process cannot access the file because it is being used by another process.

我仅尝试了webClient.DownloadFile()而不发生任何事件，但是它引发了相同的错误.如果我也不要处置，则会引发相同的错误.我该怎么办?

I tried webClient.DownloadFile() only without an event but it throws same error. Same error is throwed if i do not dispose too. What can i do ?

临时解决方法可能是Sleep()方法，但不是防弹措施.

Temporary workaround may be Sleep() method but its not bullet proof.

谢谢

我尝试了标准处理的第二种方法，但是代码有误

I tried second approach with standard handling but i have mistake in the code

  using (WebClient webClient = new WebClient())
                {
                    // nastaveni ze webClient ma pouzit Windows Authentication
                    webClient.UseDefaultCredentials = true;
                    // <--- I HAVE CONVERT ASYNC ERROR IN THIS LINE
                    webClient.DownloadFileCompleted += new DownloadDataCompletedEventHandler(HandleDownloadDataCompleted);

                    // spusteni stahovani
                    webClient.DownloadFile(new Uri("http://czprga2001/Logio_ZelenyKyblik/Export.ashx"), TempDirectory + PSFileName);
                }

public delegate void DownloadDataCompletedEventHandler(string fileName);
        public event DownloadDataCompletedEventHandler DownloadDataCompleted;
        static void HandleDownloadDataCompleted(string fileName)
        { 
            ExcelToCsv(fileName);
        }

方法3 我尝试了这段代码

approach 3 I tried this code

while (true)
                {
                    if (isFileLocked(downloadedFile))
                    {
                        System.Threading.Thread.Sleep(5000); //wait 5s
                        ExcelToCsv(fileName);
                        break;
                    }
                }

似乎永远无法访问:/我不明白.

and it seems that it is never accessible :/ I dont get it.

推荐答案

尝试使用DownloadFile而不是DownloadFileAsync，就像在Edit 1中一样:

Try to use DownloadFile instead of DownloadFileAsync, as you do in Edit 1, like this:

string filename=Path.Combine(TempDirectory, PSFileName);
using (WebClient webClient = new WebClient())
                {
                    // nastaveni ze webClient ma pouzit Windows Authentication
                    webClient.UseDefaultCredentials = true;    
                    // spusteni stahovani
                    webClient.DownloadFile(new Uri("http://czprga2001/Logio_ZelenyKyblik/Export.ashx"), filename);
                }
ExcelToCsv(filename);  //No need to create the event handler if it is not async

在您的示例中，您似乎不需要异步下载，因此请使用同步下载，并避免可能的相关问题，例如此处.

From your example it seems that you do not need asynchronous download, so use synchronous download and avoid possible related problems like here.

还可以使用Path.Combine组合路径的一部分，例如文件夹和文件名.

Also use Path.Combine to combine parts of a path like folder and filename.

也有可能它被其他东西锁定，请使用Sysinternals Process Explorer的Find DLL或Handle函数进行检查.

There is also a chance that it is locked by something else, use Sysinternals Process Explorer's Find DLL or Handle function to check it.

使用本地磁盘存储下载的文件，以防止网络出现问题.

Use local disk to store downloaded file to prevent problems with network.

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