我正在尝试从互联网下载多个文件并等待所有文件完成。这是我正在运行的 C# 控制台应用程序,因此不需要进度条事件处理程序。然而,即使所有文件尚未下载,它目前也只是继续执行代码。
- 1.下载所有文件!
- 2.完成下载文件A
- 3.所有文件下载完毕!
- 4.文件B下载完成
- 5.C文件下载完成
您将如何等待所有异步下载文件完成。
private void DownloadMultipleFiles(List<DocumentObject> doclist)
{
foreach(var value in doclist){
try
{
using (WebClient webClient = new WebClient())
{
string downloadToDirectory = @Resources.defaultDirectory + value.docName;
webClient.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
webClient.DownloadFileCompleted += client_DownloadFileCompleted;
webClient.DownloadFileAsync(new Uri(value.docUrl), @downloadToDirectory);
//Add them to the local
Context.listOfLocalDirectories.Add(downloadToDirectory);
}
}
catch (Exception)
{
Errors.printError("Failed to download File: " + value.docName);
}
}
}
The DownloadFileAsync
/DownloadFileCompleted
的成员WebClient
使用基于事件的异步模式 http://msdn.microsoft.com/en-us/library/ms228969.aspx。如果你想使用async
and await
,你应该使用基于任务的异步模式 http://msdn.microsoft.com/en-us/library/hh873175.aspx.
在这种情况下,您应该使用DownloadFileTaskAsync member http://msdn.microsoft.com/en-us/library/hh193917.aspx, 像这样:
private async Task DownloadFileAsync(DocumentObject doc)
{
try
{
using (WebClient webClient = new WebClient())
{
string downloadToDirectory = @Resources.defaultDirectory + doc.docName;
webClient.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;
await webClient.DownloadFileTaskAsync(new Uri(doc.docUrl), @downloadToDirectory);
//Add them to the local
Context.listOfLocalDirectories.Add(downloadToDirectory);
}
}
catch (Exception)
{
Errors.printError("Failed to download File: " + doc.docName);
}
}
private async Task DownloadMultipleFilesAsync(List<DocumentObject> doclist)
{
await Task.WhenAll(doclist.Select(doc => DownloadFileAsync(doc)));
}
请注意,您的Context.listOfLocalDirectories.Add
and Errors.printError
方法应该是线程安全的。
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