如果你不打擾閱讀整個文本,可以跳到最後兩個點:對C#與隊列列表異步下載
這個網站已經幫助我的時候一打已經過去,但現在我真的需要幫助。
的問題如下:
首先,我用show UI選項一起使用的DownloadFile功能。這很好,但用戶界面很醜,並沒有太多可用的選項。
然後,我切換到DownloadFileAsync與改變的進度事件,以基本上有我自己的用戶界面。我遇到的唯一問題是我循環訪問程序必須下載的文件列表,並調用下載函數(調用DownloadAsync函數)。就像這樣:
foreach (ListViewItem t in themeList.CheckedItems) { DownloadFile(file to be downloaded); }
但顯然這並沒有工作,因爲DownloadFileAsync功能不支持在同一時間多個呼叫,因爲沒有排隊系統,如DownloadFile了,所以它會只下載第一稱爲文件。 因此,我所做的是創建一個函數,將要下載的文件添加到數組中,並通過列表使背景工作循環,然後等待調用DownloadAsync,直到完成上一個下載爲止。這有點解決了。下面是代碼:
#region "Download functions" //Function that converts download speed to a nice user friendly format private static string BpsToString(double bps) { var m = new string[] { "bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB" }; var i = 0; while (bps >= 0.9 * 1024) { bps /= 1024; i++; } return String.Format("{0:0.00} {1}/sec", bps, m[i]); } private bool _complete = false; private string _speed; private int _secondsRemaining = -1; private long _transferred = 0; private Stopwatch _sw = new Stopwatch(); private List<string[]> _fd = new List<string[]>(); private void DownloadFile(string url, string des, bool overwrite = false) { if (overwrite) //if the file needs to be overwritten or not { if (File.Exists(des)) File.Delete(des); } else { if (File.Exists(des)) return; } if (!Directory.Exists(Path.GetDirectoryName(des))) //create the directory if it doesn't exist Directory.CreateDirectory(Path.GetDirectoryName(des)); string[] file = {url, des}; _fd.Add(file); //add file to queue list if(!backgroundDownloader.IsBusy) //if downloader isn't doing anything, start it again backgroundDownloader.RunWorkerAsync(); } //function called by the backgroundworker to actually download the file private void ContinueDownloadFile(string url, string des) { var webClient = new WebClient(); webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed); webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged); webClient.DownloadFileAsync(new Uri(_fd[0][0]), _fd[0][1]); } //when download completed, set progress bar to 0% and remove the first (0) download from the queue private void Completed(object sender, AsyncCompletedEventArgs e) { SetProgressText("Idle"); SetProgressValue(0); if(_fd.Count != 0) _fd.RemoveAt(0); _complete = true; //if it's complete, set to true so the backgroundworker knows it can start the next download } //progress bar value change and status change for download speed etc... private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e) { if(progressLabel.Text == "Idle") SetProgressText("Downloading..."); if (_sw.Elapsed >= TimeSpan.FromSeconds(1)) { _sw.Stop(); var bytes = e.BytesReceived - _transferred; var bps = bytes * 1000.0/_sw.Elapsed.TotalMilliseconds; _speed = BpsToString(bps); _secondsRemaining = (int)((e.TotalBytesToReceive - e.BytesReceived)/bps); _transferred = e.BytesReceived; _sw.Reset(); _sw.Start(); SetProgressText("Downloading: " + e.ProgressPercentage + "% | Seconds remaining: " + _secondsRemaining + " | Files remaining: " + _fd.Count + " | Speed: " + _speed); } SetProgressValue(e.ProgressPercentage); } //the backgroundworker who starts the downloads from the list one by one private void BackgroundDownloaderDoWork(object sender, DoWorkEventArgs e) { while (_fd.Count != 0) { _sw.Start(); _complete = false; //let the backgroundworker wait till the download is complete ContinueDownloadFile(_fd[0][0], _fd[0][1]); while(!_complete) //let it wait here Thread.Sleep(100); _sw.Stop(); _sw.Reset(); } } #endregion
所以basicly我的下一個問題是,程序必須等待與執行任何代碼,直至下載完成。我做這個做:
while (_fd.Count != 0) Application.DoEvents();
這顯然不是最好的解決辦法,因爲他們可以通過點擊其他的事情,而下載是忙碌的,但是,是的Thread.Sleep也只是凍結一切。 相反,我會在主窗體頂部重點放置一個等待窗體(也許這裏是一個進度條,而不是主窗體),所以它們不能單擊主窗體並將Thread.Sleep放在主窗體上形成?
你會如何解決這個問題?你是否還會使用循環遍歷文件數組的背景工作,或者是否有更簡單,更高效的方法。也許不使用DownloadFileAsync,但手動套接字下載?
我basicly想要的是同步下載文件,但有自己的UI(所以我需要使用異步下載功能)。哈哈
我希望我通知你足夠。提前致謝。
也許這是「TL; DR」的信息? –
我會讓它更短,因爲它確實包含一些不必要的東西 – d0ggy
你對子彈#5的計劃聽起來是最好的方式。您也可以嘗試使用任務並行庫(TPL)。它可以簡化併發下載調用,並且可以使用同步文件下載器。 –