Question

我正在尝试制作一个简单的下载管理器。它有效。问题是如果我添加一个进度条来通知用户我得到了这个异常

此流不支持搜索操作

 while ((readed = ReadFrom.Read(read, 0, read.Length)) > 0)
            {

                strLocal.Write(read, 0, readed);
                **UpdateProgress(ReadFrom.Length, strLocal.Length);// throws exception**
            }

这是所有代码

  private void button1_Click(object sender, EventArgs e)
        {
            req = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
            res = (HttpWebResponse)req.GetResponse();
            Int64 contentlength = res.ContentLength;
            WebClient wc = new WebClient();
            Stream ReadFrom= wc.OpenRead(new Uri(url));

            strLocal = new FileStream(@"E:\\xxx.tar.gz", FileMode.Create, FileAccess.Write, FileShare.None);
            byte[]read=new byte[1024];

            int readed = 0;
            while ((readed = ReadFrom.Read(read, 0, read.Length)) > 0)
            {

                strLocal.Write(read, 0, readed);
                UpdateProgress(ReadFrom.Length, strLocal.Length);
            }

            strLocal.Close();
            ReadFrom.Close();

        }

        private void UpdateProgress(long Filesize, long readedBytes)
        {
          //  progressBar1.Maximum = 100;
         int downloaded =Convert.ToInt32((readedBytes * 100) / Filesize);
         progressBar1.Value = downloaded;
        }

这里有什么问题？

@Edit

        HttpWebRequest req;
        HttpWebResponse res;
        Stream strLocal;
        Stream ResponseStr;
        byte[] bytes = null;
        Thread thr;
        delegate void UpdateCallBack(long l1, long l2);
        public Form1()
        {
            InitializeComponent();
        }
        string url="https://www.unrealircd.org/downloads/Unreal3.2.10.3.tar.gz";
        ////string url2 = "http://www.microsoft.com/en-us/download/confirmation.aspx?id=34794&6B49FDFB-8E5B-4B07-BC31-15695C5A2143=1";
        string filename = @"C:\\Unreal3.2.10.3.tar.gz";
        private void Form1_Load(object sender, EventArgs e)
        {

        }



        private void button1_Click(object sender, EventArgs e)
        {
            thr = new Thread(download);
            thr.Start();

        }

private void download()
{
            req = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
            res = (HttpWebResponse)req.GetResponse();

            Int64 contentlength = res.ContentLength;

            ResponseStr = res.GetResponseStream();

            strLocal = new FileStream(@"E:\\xxx.tar.gz", FileMode.Create, FileAccess.Write, FileShare.None);
            byte[]read=new byte[1024];

            int readed = 0;
            while ((readed = ResponseStr.Read(read, 0, read.Length)) > 0)
            {

                strLocal.Write(read, 0, readed);
                this.Invoke(new UpdateCallBack(this.UpdateProgress), new object[] {ResponseStr.Length,strLocal.Length });


            }

            strLocal.Close();
            ResponseStr.Close();
}

        private void UpdateProgress(long Filesize, long readedBytes)
        {

         int updated =Convert.ToInt32((readedBytes * 100) / Filesize);
         progressBar1.Value = updated;
        }

@ EDIT2

private void download()
{
            req = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
            res = (HttpWebResponse)req.GetResponse();

            Int64 contentlength = res.ContentLength;

            ResponseStr = res.GetResponseStream();


            strLocal = new FileStream(@"E:\\xxx.tar.gz", FileMode.Create, FileAccess.Write, FileShare.None);


            byte[]read=new byte[1024];

            int readed = 0;
            while ((readed = ResponseStr.Read(read, 0, read.Length)) > 0)
            {

                strLocal.Write(read, 0, readed);
                backgroundWorker1.RunWorkerAsync();
              //  this.Invoke(new UpdateCallBack(this.UpdateProgress), new object[] {ResponseStr.Length,strLocal.Length });


            }

            strLocal.Close();
            ResponseStr.Close();
}

        private void UpdateProgress(long Filesize, long readedBytes)
        {

         int updated =Convert.ToInt32((readedBytes * 100) / Filesize);
         progressBar1.Value = updated;
        }

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            UpdateProgress(ResponseStr.Length, strLocal.Length);
        }

Answer 1

您的所有操作都发生在同一个线程上。在进行下载时，应用程序会暂停UI的更新。我通常使用BackgroundWorker来更新这种情况的进度条。

Here's an MSDN resource on background workers.

根据您的编辑，以下是一些代码：

// At the class level, put this:
BackgroundWorker bw = new BackgroundWorker();
bw.WorkerReportsProgress = true; // This means we want to send updates from the background worker.

// The DoWork method handles your time consuming task, which in this case is your download method. So you can try this:
private void Download()
{
    bw.RunWorkerAsync();
}

// This should be called as a result:
private void bw_DoWork(object sender, DoWorkEventArgs e)
{
    // The worker who's progress will be updated.
    BackgroundWorker worker = sender as BackgroundWorker;

    req = (HttpWebRequest)HttpWebRequest.Create(new Uri(url));
    res = (HttpWebResponse)req.GetResponse();

    Int64 contentLength = res.ContentLength;

    ResponseStr = res.GetResponseStream();

    strLocal = new FileStream(@"E:\xxx.tar.gz", FileMode.Create, FileAccess.Write, FileShare.None);

    byte[] read = new byte[1024];

    int readed = 0;
    while((readed = ResponseStr.Read(read, 0, read.Length)) > 0)
    {
        strLocal.Write(read, 0, readed);
        // Update the worker (this uses the number you calculated)
        worker.ReportProgress(Convert.ToInt32((ResponseStr.Length * 100) / strLocal.Length));

        strLocal.Close();
        ResponseStr.Close();
    }
}

// This is called via worker.ReportProgress
private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    progressBar1.Value = e.ProgressPercentage;
}

您需要在类中定义后台工作程序，并允许它接受进度更新。

然后，无论何时需要后台工作者的方法，都需要调用RunWorkerAsync。您可以在下载方法中执行此操作，或者替换您调用下载的位置。

在你的工作班中，你会做你通常会做的所有事情，但是在你想要更新进度的情况下，你可以用必要的值来调用ReportProgress。

如果您查看上面的链接，还可以实施其他方法 - 如果您担心取消后台工作人员或者是否有错误或其他任何方法。

修改

如果您仍然收到错误，我只是意识到您可能正在尝试从Stream对象中提取长度。如果错误仍然存在，请查看this question。

Answer 2

如上所述，它与线程有关。因此，您需要在多个线程上分离操作才能更新UI。您也可以使用async和await来解决此问题。下面是一篇很好的文章，文章是关于做一些动作和更新UI。

http://www.i-programmer.info/programming/c/1514-async-await-and-the-ui-problem.html

我无法在下载文件时更新进度条

2 个答案: