如何使用进度条进行下载

Question

我想在我的 windows 表单应用程序中使用进度条。该应用程序将用于将文件从一个目录下载到另一个目录。

但是当用户点击下载按钮时，应用程序似乎什么都不做。所以我想用进度条向用户展示下载过程。

我确实搜索了进度条，但找不到 "how to use progress bar for process of downloading" 的答案。

如果有人向我解释如何使用进度条进行下载，我将非常高兴。

Answer 1

WebClient 有一个 DownloadProgressChanged-事件。将它连接到进度条，你就可以开始了。 MSDN

备注：您需要使用 DownloadDataAsync、DownloadFileAsync 或 OpenReadAsync 才能触发 DownloadProgressChanged-Event。

Answer 2

您可以使用 DownloadFileAsync 下载文件而不阻塞主线程，并设置事件处理程序以在栏中显示进度：

  private void button1_Click(object sender, EventArgs e)
    {
        WebClient webClient = new WebClient();
        string sourceFile = @"\server\test.txt";
        string destFile = @"\server2\test2.txt";
        webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(DownloadCompleted);
        webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
        webClient.DownloadFileAsync(new Uri(sourceFile), destFile);
    }

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

    private void DownloadCompleted(object sender, AsyncCompletedEventArgs e)
    {
        MessageBox.Show("The download is completed!");
    }

或者另一种方法可以使用将属性 WorkerReportsProgress 设置为 true 的 BackgroundWorker。那么你应该订阅事件 DoWork 和 ProgressChanged：在 DoWork 方法中，你将下载或传输文件的代码放在一个单独的线程上，并计算工作进度。在 ProgressChanged 方法中，只需更新进度条值。在这种情况下，您的代码将如下所示：

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        // the path of the source file
        string sourceFile = @"\shared\test.txt";
        // the path to write the file to
        string destFile = @"\shared2\test2.txt";

        FileInfo info = new FileInfo(sourceFile);
        // gets the size of the file in bytes
        Int64 size = info.Length;
        // keeps track of the total bytes downloaded so you can update the progress bar
        Int64 runningByteTotal = 0;
        using (FileStream reader = new FileStream(sourceFile, FileMode.Open, FileAccess.Read))
        {
            using (Stream writer = new FileStream(destFile, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                int iByteSize = 0;
                byte[] byteBuffer = new byte[size];
                while ((iByteSize = reader.Read(byteBuffer, 0, byteBuffer.Length)) > 0)
                {
                    // write the bytes to the file
                    writer.Write(byteBuffer, 0, iByteSize);
                    runningByteTotal += iByteSize;
                    // calculate the progress
                    double index = (double)(runningByteTotal);
                    double total = (double)byteBuffer.Length;
                    double progressPercentage = (index / total);
                    int iProgressPercentage = (int)(progressPercentage * 100);
                    // update the progress bar
                    backgroundWorker1.ReportProgress(iProgressPercentage);
                }
                // clean up the file stream
                writer.Close();
            }

        }
    }

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

在触发文件下载的按钮单击事件（或其他事件）中，您应该添加此代码以异步启动后台工作程序运行：

private void button1_Click(object sender, EventArgs e)
    {
        backgroundWorker1.RunWorkerAsync();
    }

如何使用进度条进行下载

how to use progressbar for process of downloading

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