Question

我想在我的Windows窗体应用程序中使用进度条。该应用程序将用于将文件从目录下载到另一个目录。

但是，当用户单击下载按钮时，应用程序似乎无所事事。所以我想向用户显示下载进度条的过程。

我确实搜索了进度条，但我找不到答案＆＃34;如何使用进度条进行下载过程＆＃34;。

如果有人向我解释如何使用进度条进行下载，我会很高兴。

Answer 1

您可以使用 DownloadFileAsync 下载文件而不会阻止主线程，并设置一个事件处理程序来显示栏中的进度：

  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BackgroundWorker，其属性 WorkerReportsProgress 设置为true。然后，您应该在DoWork方法中订阅事件 DoWork 和 ProgressChanged ：您将代码下载或在单独的线程上传输文件并计算工作进度。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）中，您应该添加此代码以启动异步运行的后台工作程序：

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

Answer 2

WebClient有一个DownloadProgressChanged - 事件。把它连接到进度条，你很高兴。 MSDN

备注：您需要使用DownloadDataAsync，DownloadFileAsync或OpenReadAsync来触发DownloadProgressChanged - 事件。

如何使用进度条进行下载

2 个答案: