等待下载完成 [英] Wait for download to complete
问题描述
我正在尝试创建一个简单的程序来下载几个文件.我已经尝试了在网上找到的一些现成的解决方案，但我无法让它按照我想要的方式工作.我正在使用这个:
I'm trying to create a simple program to download few files. I've tried some ready-made solutions I found on the web but I can't manage to make it work the way I want it to. I'm using this:
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");
});
}
我想让程序在下载完成后继续(下载下一个文件/显示OK"消息/执行下一行代码中的任何操作).在当前的形式中，如果我把例如.
I'd like to make the program continue (download next file / show the "OK" message / do whatever is in the next line of code) AFTER the download has finished. In the current form, if I'd put eg.
private void button1_Click(object sender, EventArgs e)
{
startDownload(url, localpath + @"file.zip");
textBoxLog.AppendText("the cake is a lie");
}
它首先向我显示此文本，然后确定".
it's showing me this text first and "OK" later.
我是从 c#/.net 开始的，我之前从未学过面向对象编程，所以这对我来说是双重挑战，我自己无法弄清楚.如果能提供相对简单的解释，我将不胜感激.
I'm beginning with c#/.net and I've never learned object-oriented programming before so it's kind of double challenge for me and I can't figure it out by myself. I would be really grateful for relatively easy explanation.
推荐答案
您可以通过 Application.DoEvents() 像这样:
You can have startDownload wait for the asynchronous file download through Application.DoEvents() like this:
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;
});
}
还有下载队列...
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));
}
}
但是，我认为您最好阅读有关 HttpWebRequest 并使用适当的检查和事件编写您自己的下载器类...这是 Hemanshu Bhojak 的一个很好的例子(来源)，你可以展开:
However, I think you're better off reading about HttpWebRequest and writing your own downloader class with proper checks and events... Here's a pretty good example by Hemanshu Bhojak (Source) that you can expand upon:
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);
}
}
}
示例用法:
Task.Run(() => new Downloader().Download(downloadString, saveToString)).Wait();
大致如下:
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;
}
}
这篇关于等待下载完成的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
