异步下载时设置用户状态答案

【问题标题】：Setting the user state when downloading asynchronously异步下载时设置用户状态
【发布时间】：2009-08-01 09:34:17
【问题描述】：

VS 2008 SP1

我正在使用网络客户端异步下载一些文件。

我有 5 个文件要下载。

但是，我想监控每次下载，想把用户状态设置为文件名，所以在ProgressCompletedEvent中可以查看用户状态，看看哪个文件完成了？

他是我正在尝试做的一个简短的代码 sn-p。

// This function will be called for each file that is going to be downloaded.
// is there a way I can set the user state so I know that the download 
// has been completed 
// for that file, in the DownloadFileCompleted Event? 
private void DownloadSingleFile()
{
    if (!wb.IsBusy)
    {        
        //  Set user state here       
        wb.DownloadFileAsync(new Uri(downloadUrl), installationPath);
    }
}


void wb_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    Console.WriteLine("File userstate: [ " + e.UserState + " ]");   
}

void wb_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
    Console.WriteLine("File userstate: [ " + e.UserState + " ]");   

    double bytesIn = double.Parse(e.BytesReceived.ToString());
    double totalBytes = double.Parse(e.TotalBytesToReceive.ToString());
    double percentage = bytesIn / totalBytes * 100;

    progressBar1.Value = int.Parse(Math.Truncate(percentage).ToString());

}

【问题讨论】：

标签： c# webclient

【解决方案1】：

您可以将任何对象作为第三个 参数传递给DownloadFileAsync() 调用，然后将其作为userState 取回。在您的情况下，您可以简单地传递您的文件名。

【讨论】：

client.UploadFileCompleted += new UploadFileCompletedEventHandler(UploadFileCallback);Client.UploadFileAsync(uri, "STOR", sourceFile,fileName);私人无效UploadFileCallback（对象发送者，UploadFileCompletedEventArgs e）{MessageBox.Show（e.UserState.ToString（））; . . . }

【解决方案2】：

这样的事情怎么样：

private void BeginDownload(
    string uriString,
    string localFile,
    Action<string, DownloadProgressChangedEventArgs> onProgress,
    Action<string, AsyncCompletedEventArgs> onComplete)
{
    WebClient webClient = new WebClient();

    webClient.DownloadProgressChanged +=
        (object sender, DownloadProgressChangedEventArgs e) =>
            onProgress(localFile, e);

    webClient.DownloadFileCompleted +=
        (object sender, AsyncCompletedEventArgs e) =>
            onComplete(localFile, e);

    webClient.DownloadFileAsync(new Uri(uriString), localFile);
}

在您的调用代码中，您可以使用如下代码：

Action<string, DownloadProgressChangedEventArgs> onProgress =
    (string localFile, DownloadProgressChangedEventArgs e) =>
    {
        Console.WriteLine("{0}: {1}/{2} bytes received ({3}%)",
            localFile, e.BytesReceived,
            e.TotalBytesToReceive, e.ProgressPercentage);
    };

Action<string, AsyncCompletedEventArgs> onComplete =
    (string localFile, AsyncCompletedEventArgs e) =>
    {
        Console.WriteLine("{0}: {1}", localFile,
            e.Error != null ? e.Error.Message : "Completed");
    };

downloader.BeginDownload(
    @"http://url/to/file",
    @"/local/path/to/file",
    onProgress, onComplete);

如果您不介意让它过于可重用，您实际上可以将传入的函数全部丢弃，直接在代码中编写 lambda 表达式：

private void BeginDownload(string uriString, string localFile)
{
    WebClient webClient = new WebClient();

    webClient.DownloadProgressChanged +=
        (object sender, DownloadProgressChangedEventArgs e) =>
            Console.WriteLine("{0}: {1}/{2} bytes received ({3}%)",
                localFile, e.BytesReceived,
                e.TotalBytesToReceive, e.ProgressPercentage);

    webClient.DownloadFileCompleted +=
        (object sender, AsyncCompletedEventArgs e) =>
            Console.WriteLine("{0}: {1}", localFile,
                e.Error != null ? e.Error.Message : "Completed");

    webClient.DownloadFileAsync(new Uri(uriString), localFile);
}

调用两次，这将为您提供类似这样的输出

/path/to/file1：收到 265/265 个字节 (100%)
/path/to/file1：已完成
/path/to/file2: 收到 2134/2134 字节 (100%)
/path/to/file2: 完成

【讨论】：