c# - 使用带有进度报告的 Async/Await 下载并提取 zip 文件

Question

我想实现一个可重用的类，该类将有助于下载给定的 zip 文件并将其解压缩，同时使用 C# 5 等待/异步功能报告进度。

我对此很陌生，目前正在努力解决这个问题。到目前为止，这是我的安装程序类:

class Installer
{
    Button saveButton;
    ProgressBar progressBar;
    Label statusLabel;
    Boolean downloadDone;

    public Installer(Button _saveButton, ProgressBar _progressBar, Label _statusLabel)
    {
        saveButton = _saveButton;
        progressBar = _progressBar;
        statusLabel = _statusLabel;
    }

    public async void Start(string fileUrl)
    {
        saveButton.BeginInvoke((Action)(() => {
            saveButton.Enabled = false;
        }));

        Task<bool> downloadArchiveTask = DownloadArchiveAsync(fileUrl);

        bool downloadArchiveDone = await downloadArchiveTask;

        if (downloadArchiveDone)
            statusLabel.BeginInvoke((Action)(() => {
                statusLabel.Text = "Download Completed";
            }));
    }

    async Task<bool> DownloadArchiveAsync(string fileUrl)
    {
        var downloadLink = new Uri(fileUrl);
        var saveFilename = Path.GetFileName(downloadLink.AbsolutePath);

        DownloadProgressChangedEventHandler DownloadProgressChangedEvent = (s, e) =>
        {
            progressBar.BeginInvoke((Action)(() => {
                progressBar.Value = e.ProgressPercentage;
            }));

            var downloadProgress = string.Format("{0} MB / {1} MB",
                    (e.BytesReceived / 1024d / 1024d).ToString("0.00"),
                    (e.TotalBytesToReceive / 1024d / 1024d).ToString("0.00"));

            statusLabel.BeginInvoke((Action)(() => {
                statusLabel.Text = "Downloading " + downloadProgress + " ...";
            }));
        };

        AsyncCompletedEventHandler AsyncCompletedEvent = (s, e) =>
        {
            // Todo: Extract
            downloadDone = true;
        };

        using (WebClient webClient = new WebClient())
        {
            webClient.DownloadProgressChanged += DownloadProgressChangedEvent;
            webClient.DownloadFileCompleted += AsyncCompletedEvent;
            webClient.DownloadFileAsync(downloadLink, saveFilename);
        }

        while (!downloadDone) ;

        return true;
    }
}

我是这样用的:

(new Installer(startBtn, progressBar, statusLabel)).Start("http://nginx.org/download/nginx-1.9.4.zip");

我不完全确定我是否正确实现了这一点。 Visual Studio 给我以下警告:

DownloadArchiveAsync - This async method lacks 'await' operators and will run synchronously.

另请注意；我目前没有合适的方法来检测下载何时完成，所以我正在使用 bool 和 while 循环 - 不确定是否也推荐这样做。

使用 async/await 异步下载 zip 文件并报告进度的正确方法是什么？

---

编辑

在深入研究之后，我找到了一种可能的解决方案。我已经实现了这个方法:

async Task IsDownloadDone()
{
    await Task.Run(() =>
    {
        while (!downloadDone) ;
    });
}

并像这样更新了 DownloadArchiveAsync 返回:

await IsDownloadDone();
return true;

完整代码现在如下所示:http://pastebin.com/MuW0386K

这是实现它的正确方法吗？

Answer 1

你可以用这样的东西替换 DownloadArchiveAsync，它实际上会异步工作:

async Task<bool> DownloadArchiveAsync( string fileUrl )
{
    var downloadLink = new Uri( fileUrl );
    var saveFilename = System.IO.Path.GetFileName( downloadLink.AbsolutePath );

    DownloadProgressChangedEventHandler DownloadProgressChangedEvent = ( s, e ) =>
    {
        progressBar.BeginInvoke( (Action)(() =>
        {
            progressBar.Value = e.ProgressPercentage;
        }) );

        var downloadProgress = string.Format( "{0} MB / {1} MB",
                (e.BytesReceived / 1024d / 1024d).ToString( "0.00" ),
                (e.TotalBytesToReceive / 1024d / 1024d).ToString( "0.00" ) );

        statusLabel.BeginInvoke( (Action)(() =>
        {
            statusLabel.Text = "Downloading " + downloadProgress + " ...";
        }) );
    };

    using (WebClient webClient = new WebClient())
    {
        webClient.DownloadProgressChanged += DownloadProgressChangedEvent;
        await webClient.DownloadFileTaskAsync( downloadLink, saveFilename );
    }

    return true;
}

编辑:我在 MSDN 中找到了 DownloadFileTaskAsync，这让事情变得更漂亮了。

方法上的

async 表示此方法使用 await。因此，请使用“WebClient”中的可等待函数。