c# Async下载秒表，但UI冻结某处
本文关键字：UI 冻结 Async 下载 | 更新日期: 2023-09-27 18:12:40
下面是我用来下载文件并计算剩余时间和kbps的一些代码。然后，它将通过更新文本框和进度条将这些结果发布到表单上。我遇到的问题是UI正在冻结，我认为这可能是我使用秒表的方式，但不确定。有人有意见吗?
/// Downloads the file.
private void Download_Begin()
{
web_client = new System.Net.WebClient();
web_client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(Download_Progress);
web_client.DownloadFileCompleted += new AsyncCompletedEventHandler(Download_Complete);
stop_watch = new System.Diagnostics.Stopwatch();
stop_watch.Start();
try
{
if (Program.Current_Download == "Install_Client.exe")
{
web_client.DownloadFileAsync(new Uri("http://www.website.com/Client/Install_Client.exe"), @"C:'Downloads'Install_Client.exe");
}
else
{
web_client.DownloadFileAsync(new Uri((string.Format("http://www.website.com/{0}", Program.Current_Download))), (string.Format(@"C:'Downloads'{0}", Program.Current_Download)));
}
}
catch(Exception)
{
stop_watch.Stop();
}
Program.Downloading = true;
Download_Success = false;
}
/// -------------------
/// Tracks download progress.
private void Download_Progress(object sender, DownloadProgressChangedEventArgs e)
{
double bs = e.BytesReceived / stop_watch.Elapsed.TotalSeconds;
this.label_rate.Text = string.Format("{0} kb/s", (bs / 1024d).ToString("0.00"));
long bytes_remaining = e.TotalBytesToReceive - e.BytesReceived;
double time_remaining_in_seconds = bytes_remaining / bs;
var remaining_time = TimeSpan.FromSeconds(time_remaining_in_seconds);
string hours = remaining_time.Hours.ToString("00");
if (remaining_time.Hours > 99)
{
hours = remaining_time.Hours.ToString("000");
}
this.time_remaining.Text = string.Format("{0}::{1}::{2} Remaining", hours, remaining_time.Minutes.ToString("00"), remaining_time.Seconds.ToString("00"));
progressBar1.Maximum = (int)e.TotalBytesToReceive / 100;
progressBar1.Value = (int)e.BytesReceived / 100;
if (e.ProgressPercentage == 100)
{
Download_Success = true;
}
}
/// -------------------------
UI线程可能由于各种原因冻结，尽管您正在调用异步下载函数。防止UI冻结的一种方法是从与UI不同的线程中调用文件下载。例如，你可以用BackgroundWorker来完成这个任务，并通过线程安全调用来安全地修改表单的控件，或者简单地说，用BeginInvoke()调用来包装在非ui线程中执行的代码。
private void button1_Click(object sender, EventArgs e)
{
BackgroundWorker worker = new BackgroundWorker();
worker.DoWork += Worker_DoWork;
worker.RunWorkerAsync();
}
private void Worker_DoWork(object sender, DoWorkEventArgs e)
{
Download_Begin();
}
/// Downloads the file.
private void Download_Begin()
{
web_client = new System.Net.WebClient();
web_client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(Download_Progress);
web_client.DownloadFileCompleted += new AsyncCompletedEventHandler(Download_Complete);
stop_watch = new System.Diagnostics.Stopwatch();
stop_watch.Start();
try
{
if (Program.Current_Download == "Install_Client.exe")
{
web_client.DownloadFileAsync(new Uri("http://www.website.com/Client/Install_Client.exe"), @"C:'Downloads'Install_Client.exe");
}
else
{
web_client.DownloadFileAsync(new Uri((string.Format("http://www.website.com/{0}", Program.Current_Download))), (string.Format(@"C:'Downloads'{0}", Program.Current_Download)));
}
}
catch (Exception)
{
stop_watch.Stop();
}
Program.Downloading = true;
Download_Success = false;
}
/// -------------------
/// Tracks download progress.
private void Download_Progress(object sender, DownloadProgressChangedEventArgs e)
{
this.BeginInvoke(new Action(() =>
{
double bs = e.BytesReceived / stop_watch.Elapsed.TotalSeconds;
this.label_rate.Text = string.Format("{0} kb/s", (bs / 1024d).ToString("0.00"));
long bytes_remaining = e.TotalBytesToReceive - e.BytesReceived;
double time_remaining_in_seconds = bytes_remaining / bs;
var remaining_time = TimeSpan.FromSeconds(time_remaining_in_seconds);
string hours = remaining_time.Hours.ToString("00");
if (remaining_time.Hours > 99)
{
hours = remaining_time.Hours.ToString("000");
}
this.time_remaining.Text = string.Format("{0}::{1}::{2} Remaining", hours, remaining_time.Minutes.ToString("00"), remaining_time.Seconds.ToString("00"));
progressBar1.Maximum = (int)e.TotalBytesToReceive / 100;
progressBar1.Value = (int)e.BytesReceived / 100;
if (e.ProgressPercentage == 100)
{
Download_Success = true;
}
}));
}
关于你的代码的一些想法:
- 当异常发生时不需要关闭秒表，秒表内部不做任何工作，它只是在您启动秒表时记住当前时间，并在访问经过的时间时计算差异。
- 当您捕获所有异常时，不需要提供Exception类(即
catch而不是catch(Exception))。 - 仅在
DownloadFileCompleted事件中标记下载完成，而不是在DownloadProgressChanged事件中标记下载完成，因为即使下载尚未完成，ProgressPercentage也可以为100。 - 当使用异步代码时，在调用async方法之前，而不是之后，初始化状态变量(在您的情况下是
Download_Success和Program.Downloading)总是更好。
现在大约冻结。DownloadProgreesChanged可以经常被WebClient触发，因此UI线程可以被更新消息淹没。您需要拆分报表进度并更新UI代码。UI应该定时更新，例如，每秒两次。下面是非常粗略的代码示例:
// Put timer on your form, equivalent to:
// Update_Timer = new System.Windows.Forms.Timer();
// Update_Timer.Interval = 500;
// Update_Timer.Tick += Timer_Tick;
private void Download_Begin()
{
web_client = new System.Net.WebClient();
web_client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(Download_Progress);
web_client.DownloadFileCompleted += new AsyncCompletedEventHandler(Download_Complete);
Program.Downloading = true;
Download_Success = false;
stop_watch = System.Diagnostics.Stopwatch.StartNew();
Update_Timer.Start();
web_client.DownloadFileAsync(new Uri("uri"), "path");
}
private int _Progress;
private void Download_Progress(object sender, DownloadProgressChangedEventArgs e)
{
_Progress = e.ProgressPercentage;
}
private void Download_Complete(object sender, AsyncCompletedEventArgs e)
{
Update_Timer.Stop();
Program.Downloading = false;
Download_Success = true;
}
private void Timer_Tick(object sender, EventArgs e)
{
// Your code to update remaining time and speed
// this.label_rate.Text = ...
// this.time_remaining.Text = ...
progressBar1.Value = _Progress;
}