C# 异步下载多个文件并等待所有文件完成，然后再执行其余代码
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Download multiple files async and wait for all of them to finish before executing the rest of the code
提问by user2100493
I am trying to download multiple files from the internet and await for all of them to finish. This is a C# console application that I am running, so no progress bar event handler should be necessary. However it currently just continues to execute code even though all files have not been downloaded.
我正在尝试从 Internet 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。但是，即使尚未下载所有文件，它目前也只是继续执行代码。
- 1.Downloading all files!
- 2.Finished Download File A
- 3.Finished Downloading all files!
- 4.Finished Downloading File B
- 5.Finished Downloading File C
- 1.下载所有文件！
- 2.完成下载文件A
- 3.完成下载所有文件！
- 4.完成下载文件B
- 5.完成下载文件C
How would you await till all async download files are finished.
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);
}
}
}
采纳答案by Stephen Cleary
The DownloadFileAsync/DownloadFileCompletedmembers of WebClientuse the Event-based Asynchronous Pattern. If you want to use asyncand await, you should be using the Task-based Asynchronous Pattern.
在DownloadFileAsync/DownloadFileCompleted的成员WebClient使用基于事件的异步模式。如果你想使用asyncand await，你应该使用基于任务的异步模式。
In this case, you should use the DownloadFileTaskAsyncmember, as such:
在这种情况下，您应该使用DownloadFileTaskAsync成员，如下所示：
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)));
}
Please note that your Context.listOfLocalDirectories.Addand Errors.printErrormethods should be threadsafe.
请注意，您的Context.listOfLocalDirectories.Add和Errors.printError方法应该是线程安全的。
