等待下载完成(Wait for download to complete)

我试图创建一个简单的程序来下载一些文件。我已经尝试了一些现成的解决方案，我在网上找到，但我不能设法让它工作，我希望它的方式。我使用的是这样的：

    private void startDownload(string toDownload, string saveLocation)
    {
        Thread thread = new Thread(() =>
        {
            WebClient client = new WebClient();
            client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
            client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted);
            client.DownloadFileAsync(new Uri(toDownload), saveLocation);
        });
        thread.Start();
    }

    void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
    {
        this.BeginInvoke((MethodInvoker)delegate
        {
            double bytesIn = double.Parse(e.BytesReceived.ToString());
            double totalBytes = double.Parse(e.TotalBytesToReceive.ToString());
            double percentage = bytesIn / totalBytes * 100;
            labelPercentage.Text = "Downloading " + Convert.ToInt32(percentage) + "%  -  " + Convert.ToInt32(bytesIn / 1024) + " / " + Convert.ToInt32(totalBytes / 1024) + " kB";
            progressBar1.Value = int.Parse(Math.Truncate(percentage).ToString());
        });
    }

    void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
    {
        this.BeginInvoke((MethodInvoker)delegate
        {
            textBoxLog.AppendText("OK");
        });
    }

我想使程序继续（下载下一个文件/显示“OK”消息/为所欲为是在下一行代码）后下载完成。在目前的形式，如果我把如。

    private void button1_Click(object sender, EventArgs e)
    {
        startDownload(url, localpath + @"\file.zip");
        textBoxLog.AppendText("the cake is a lie");
    }

它是第一个我看这个文本和“OK”之后。

我用C＃/。NET开始，我从来没有学过面向对象编程之前，所以它是一种对我的双重挑战的，我不能由我自己看着办吧。我会是比较容易解释真的很感激。

Answer 1:

你可以有startDownload等待通过异步文件下载Application.DoEvents（）是这样的：

private bool downloadComplete = false;

private void startDownload(Uri toDownload, string saveLocation)
{
    string outputFile = Path.Combine(saveLocation, Path.GetFileName(toDownload.AbsolutePath));

    WebClient client = new WebClient();
    client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged);
    client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted);
    client.DownloadFileAsync(toDownload, outputFile);

    while (!downloadComplete)
    {
        Application.DoEvents();
    }

    downloadComplete = false;
}

void client_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
{
// No changes in this method...
}

void client_DownloadFileCompleted(object sender, AsyncCompletedEventArgs e)
{
    this.BeginInvoke((MethodInvoker)delegate
    {
        textBoxLog.AppendText("OK");
        downloadComplete = true;
    });
}

和下载队列...

private void button1_Click(object sender, EventArgs e)
{
    FireDownloadQueue(urls, localpath);
    textBoxLog.AppendText("the cake is a lie");
}

private async void FireDownloadQueue(Uri[] toDownload, string saveLocation)
{
    foreach (var url in urls)
    {
        await Task.Run(() => startDownload(url, localpath));
    }
}

不过，我觉得你最好阅读有关HttpWebRequest的，写有适当的检查和事件你自己下载类......这里有一个很好的例子由Hemanshu Bhojak（来源），您可以在扩大：

public class Downloader
{
    public async Task Download(string url, string saveAs)
    {
        var httpClient = new HttpClient();
        var response = await httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Head, url));
        var parallelDownloadSuported = response.Headers.AcceptRanges.Contains("bytes");
        var contentLength = response.Content.Headers.ContentLength ?? 0;

        if (parallelDownloadSuported)
        {
            const double numberOfParts = 5.0;
            var tasks = new List<Task>();
            var partSize = (long)Math.Ceiling(contentLength / numberOfParts);

            File.Create(saveAs).Dispose();

            for (var i = 0; i < numberOfParts; i++)
            {
                var start = i*partSize + Math.Min(1, i);
                var end = Math.Min((i + 1)*partSize, contentLength);

                tasks.Add(
                    Task.Run(() => DownloadPart(url, saveAs, start, end))
                    );
            }

            await Task.WhenAll(tasks);
        }
    }

    private async void DownloadPart(string url, string saveAs, long start, long end)
    {
        using (var httpClient = new HttpClient())
        using (var fileStream = new FileStream(saveAs, FileMode.Open, FileAccess.Write, FileShare.Write))
        {
            var message = new HttpRequestMessage(HttpMethod.Get, url);
            message.Headers.Add("Range", string.Format("bytes={0}-{1}", start, end));

            fileStream.Position = start;
            await httpClient.SendAsync(message).Result.Content.CopyToAsync(fileStream);
        }
    }
}

实例：

Task.Run(() => new Downloader().Download(downloadString, saveToString)).Wait();

随着沿线的东西：

public class Downloader
{
    public event EventHandler DownloadProgress;
    DownloaderEventArgs downloaderEventArgs;

    public void DownloadStarted(DownloaderEventArgs e)
    {
        EventHandler downloadProgress = DownloadProgress;
        if (downloadProgress != null)
            downloadProgress(this, e);
    }

    // ...
}

class DownloaderEventArgs : EventArgs
{
    public string Filename { get; private set; }
    public int Progress { get; private set; }

    public DownloaderEventArgs(int progress, string filename)
    {
        Progress = progress;
        Filename = filename;
    }
    public DownloaderEventArgs(int progress) : this(progress, String.Empty)
    {
        Progress = progress;
    }
}