取消一項或多項工作 (C# 和 Visual Basic)

發行項
03/12/2013

您可以設定可用來取消非同步應用程式中的按鈕，如果不要等待它完成。您可以依照本主題中的範例，您可以將取消按鈕加入至下載一個網站內容或網站清單的應用程式。

範例會使用微調非同步應用程式 (C# 和 Visual Basic) 描述的 UI。

注意事項
若要執行此範例，您必須將 Visual Studio 2012 中， Windows 桌面上的 Visual Studio Express 2012 for或者在您的電腦上安裝 .NET Framework 4.5。

取消工作

第一個範例和 [取消] 按鈕與單一下載工作有關聯。如果您選取按鈕時，應用程式下載內容時，下載被取消。

下載範例

您可以下載完成 Windows Presentation Foundation (WPF) 專案從 Async 範例:微調應用程式中依照下列步驟執行。

解壓縮您下載的檔案，然後啟動 Visual Studio 2012。
在功能表列上，選擇 [檔案]、[開啟]、[專案/方案]。
在 [開啟專案] 對話方塊中，開啟含有範例程式碼會在解壓縮，然後開啟 AsyncFineTuningCS 或 AsyncFineTuningVB 方案的資料夾 (.sln) 檔。
在 [方案總管]，開啟 [CancelAfterOneTask] 專案的捷徑功能表，然後選取 [設定為啟始專案]。
選擇 F5 鍵執行專案。

選取 Ctrl+F5 鍵執行專案，但不偵錯。

如果您不要下載專案，您可以檢閱 MainWindow.xaml.vb 或 MainWindow.xaml.cs 檔案在這個主題的結尾。

建置範例

下列變更將 [移除] 按鈕加入至下載中心網站的應用程式。如果您不要下載或建立這個範例，您可以檢閱「完整範例一節的最終產品本主題結尾。星號標示出在程式碼檔案中的變更。

若要建置範例，逐步，請依照 < 下載範例中的」表示部分，不過，選取 [StarterCode] 為 [啟始專案] 而不是 [CancelATask]。

接著將該專案 MainWindow.xaml.vb 或 MainWindow.xaml.cs 檔案進行下列變更。

宣告一個 CancellationTokenSource 變數，cts，對所有方法的範圍存取它。

Class MainWindow

    ' ***Declare a System.Threading.CancellationTokenSource.
    Dim cts As CancellationTokenSource

public partial class MainWindow : Window
{
    // ***Declare a System.Threading.CancellationTokenSource.
    CancellationTokenSource cts;

將下列程式碼加入至 [ 取消 ]按鈕的 事件處理常式。事件處理常式會使用 CancellationTokenSource.Cancel 方法告知 cts ，當使用者要求取消。

' ***Add an event handler for the Cancel button.
Private Sub cancelButton_Click(sender As Object, e As RoutedEventArgs)

    If cts IsNot Nothing Then
        cts.Cancel()
    End If
End Sub

// ***Add an event handler for the Cancel button.
private void cancelButton_Click(object sender, RoutedEventArgs e)
{
    if (cts != null)
    {
        cts.Cancel();
    }
}

在 [開始] 按鈕的事件處理常式中進行下列變更 startButton_Click。

具現化 CancellationTokenSource， cts。

' ***Instantiate the CancellationTokenSource.
cts = New CancellationTokenSource()

// ***Instantiate the CancellationTokenSource.
cts = new CancellationTokenSource();

呼叫 AccessTheWebAsync，其為下載自指定網站的內容，以cts 屬性做為引數，送出 CancellationTokenSource.Token 。如果要求取消， Token 屬性傳播訊息。將會顯示訊息的 catch 區塊，如果使用者選擇取消下載作業。下列程式碼顯示變更。

Try
    ' ***Send a token to carry the message if cancellation is requested.
    Dim contentLength As Integer = Await AccessTheWebAsync(cts.Token)

    resultsTextBox.Text &=
        String.Format(vbCrLf & "Length of the downloaded string: {0}." & vbCrLf, contentLength)

    ' *** If cancellation is requested, an OperationCanceledException results.
Catch ex As OperationCanceledException
    resultsTextBox.Text &= vbCrLf & "Download canceled." & vbCrLf

Catch ex As Exception
    resultsTextBox.Text &= vbCrLf & "Download failed." & vbCrLf
End Try

try
{
    // ***Send a token to carry the message if cancellation is requested.
    int contentLength = await AccessTheWebAsync(cts.Token);
    resultsTextBox.Text +=
        String.Format("\r\nLength of the downloaded string: {0}.\r\n", contentLength);
}
// *** If cancellation is requested, an OperationCanceledException results.
catch (OperationCanceledException)
{
    resultsTextBox.Text += "\r\nDownload canceled.\r\n";
}
catch (Exception)
{
    resultsTextBox.Text += "\r\nDownload failed.\r\n";
}

在 AccessTheWebAsync，請使用 GetAsync HttpClient.GetAsync(String, CancellationToken) 方法的多載 HttpClient 型別來下載網站的內容。傳入 ct，AccessTheWebAsync的參數CancellationToken ，做為第二個引數。如果使用者選取 [取消] 按鈕，此語彙基元會傳送訊息。

下列程式碼顯示在 AccessTheWebAsync中的這些變更。

' ***Provide a parameter for the CancellationToken.
Async Function AccessTheWebAsync(ct As CancellationToken) As Task(Of Integer)

    Dim client As HttpClient = New HttpClient()

    resultsTextBox.Text &=
        String.Format(vbCrLf & "Ready to download." & vbCrLf)

    ' You might need to slow things down to have a chance to cancel.
    Await Task.Delay(250)

    ' GetAsync returns a Task(Of HttpResponseMessage). 
    ' ***The ct argument carries the message if the Cancel button is chosen.
    Dim response As HttpResponseMessage = Await client.GetAsync("https://msdn.microsoft.com/en-us/library/dd470362.aspx", ct)

    ' Retrieve the website contents from the HttpResponseMessage.
    Dim urlContents As Byte() = Await response.Content.ReadAsByteArrayAsync()

    ' The result of the method is the length of the downloaded website.
    Return urlContents.Length
End Function

// ***Provide a parameter for the CancellationToken.
async Task<int> AccessTheWebAsync(CancellationToken ct)
{
    HttpClient client = new HttpClient();

    resultsTextBox.Text +=
        String.Format("\r\nReady to download.\r\n");

    // You might need to slow things down to have a chance to cancel.
    await Task.Delay(250);

    // GetAsync returns a Task<HttpResponseMessage>. 
    // ***The ct argument carries the message if the Cancel button is chosen.
    HttpResponseMessage response = await client.GetAsync("https://msdn.microsoft.com/en-us/library/dd470362.aspx", ct);

    // Retrieve the website contents from the HttpResponseMessage.
    byte[] urlContents = await response.Content.ReadAsByteArrayAsync();

    // The result of the method is the length of the downloaded website.
    return urlContents.Length;
}

如果您無法取消，程式會產生下列輸出。
```
Ready to download.
Length of the downloaded string: 158125.
```
如果您選取 [取消] 按鈕，在程式完成下載內容之前，程式會產生下列輸出。
```
Ready to download.
Download canceled.
```

取消工作的清單。

您可以擴充前一個範例，藉由關聯 CancellationTokenSource 與每一個工作來取消執行許多工作。如果您選取 [取消] 按鈕時，您會移除未完成的工作。

下載範例

您可以下載完成 Windows Presentation Foundation (WPF) 專案從 Async 範例:微調應用程式中依照下列步驟執行。

解壓縮您下載的檔案，然後啟動 Visual Studio 2012。
在功能表列上，選擇 [檔案]、[開啟]、[專案/方案]。
在 [開啟專案] 對話方塊中，開啟含有範例程式碼會在解壓縮，然後開啟 AsyncFineTuningCS 或 AsyncFineTuningVB 方案的資料夾 (.sln) 檔。
在 [方案總管]，開啟 [CancelAfterOneTask] 專案的捷徑功能表，然後選取 [設定為啟始專案]。
選擇 F5 鍵執行專案。

選取 Ctrl+F5 鍵執行專案，但不偵錯。

如果您不要下載專案，您可以檢閱 MainWindow.xaml.vb 或 MainWindow.xaml.cs 檔案在這個主題的結尾。

建置範例

若要擴充這個範例，逐步，請依照 < 下載範例中的」表示部分，不過，選取 [CancelATask] 為 [啟始專案]。將該專案進行下列變更。星號指示在程式中的變更。

加入一個方法以建立網路位址清單。

' ***Add a method that creates a list of web addresses.
Private Function SetUpURLList() As List(Of String)

    Dim urls = New List(Of String) From
        {
            "https://msdn.microsoft.com",
            "https://msdn.microsoft.com/en-us/library/hh290138.aspx",
            "https://msdn.microsoft.com/en-us/library/hh290140.aspx",
            "https://msdn.microsoft.com/en-us/library/dd470362.aspx",
            "https://msdn.microsoft.com/en-us/library/aa578028.aspx",
            "https://msdn.microsoft.com/en-us/library/ms404677.aspx",
            "https://msdn.microsoft.com/en-us/library/ff730837.aspx"
        }
    Return urls
End Function

// ***Add a method that creates a list of web addresses.
private List<string> SetUpURLList()
{
    List<string> urls = new List<string> 
    { 
        "https://msdn.microsoft.com",
        "https://msdn.microsoft.com/en-us/library/hh290138.aspx",
        "https://msdn.microsoft.com/en-us/library/hh290140.aspx",
        "https://msdn.microsoft.com/en-us/library/dd470362.aspx",
        "https://msdn.microsoft.com/en-us/library/aa578028.aspx",
        "https://msdn.microsoft.com/en-us/library/ms404677.aspx",
        "https://msdn.microsoft.com/en-us/library/ff730837.aspx"
    };
    return urls;
}

呼叫在 AccessTheWebAsync 中的方法。

' ***Call SetUpURLList to make a list of web addresses.
Dim urlList As List(Of String) = SetUpURLList()

// ***Call SetUpURLList to make a list of web addresses.
List<string> urlList = SetUpURLList();

將下列迴圈加入 AccessTheWebAsync 中來處理清單中的每個網路位址。

' ***Add a loop to process the list of web addresses.
For Each url In urlList
    ' GetAsync returns a Task(Of HttpResponseMessage). 
    ' Argument ct carries the message if the Cancel button is chosen. 
    ' ***Note that the Cancel button can cancel all remaining downloads.
    Dim response As HttpResponseMessage = Await client.GetAsync(url, ct)

    ' Retrieve the website contents from the HttpResponseMessage.
    Dim urlContents As Byte() = Await response.Content.ReadAsByteArrayAsync()

    resultsTextBox.Text &=
        String.Format(vbCrLf & "Length of the downloaded string: {0}." & vbCrLf, urlContents.Length)
Next

// ***Add a loop to process the list of web addresses.
foreach (var url in urlList)
{
    // GetAsync returns a Task<HttpResponseMessage>. 
    // Argument ct carries the message if the Cancel button is chosen. 
    // ***Note that the Cancel button can cancel all remaining downloads.
    HttpResponseMessage response = await client.GetAsync(url, ct);

    // Retrieve the website contents from the HttpResponseMessage.
    byte[] urlContents = await response.Content.ReadAsByteArrayAsync();

    resultsTextBox.Text +=
        String.Format("\r\nLength of the downloaded string: {0}.\r\n", urlContents.Length);
}

由於 AccessTheWebAsync 顯示長度，方法不需傳回任何值。移除 return 陳述式，並且變更方法的傳回型別為 Task 而不是 Task<TResult>。
```
Async Function AccessTheWebAsync(ct As CancellationToken) As Task
```
```
async Task AccessTheWebAsync(CancellationToken ct)
```
從 startButton_Click 呼叫的方法是使用陳述式 (而不是運算式)。
```
Await AccessTheWebAsync(cts.Token)
```
```
await AccessTheWebAsync(cts.Token);
```

如果您無法取消，程式會產生下列輸出。

Length of the downloaded string: 35939.

Length of the downloaded string: 237682.

Length of the downloaded string: 128607.

Length of the downloaded string: 158124.

Length of the downloaded string: 204890.

Length of the downloaded string: 175488.

Length of the downloaded string: 145790.

Downloads complete.

如果您選取 [取消] 按鈕，在下載完成之前，輸出包含在移除之前完成下載的長度。

Length of the downloaded string: 35939.

Length of the downloaded string: 237682.

Length of the downloaded string: 128607.

Downloads canceled.

完整範例

下列章節包含每一個程式碼範例。請注意您必須增加 System.Net.Http的參考。

您可以從 Async範例:微調您的應用程式下載這個專案。

取消工作範例

下列程式碼完成 MainWindow.xaml.vb 或移除單一工作範例的 MainWindow.xaml.cs 檔案。

' Add an Imports directive and a reference for System.Net.Http.
Imports System.Net.Http

' Add the following Imports directive for System.Threading.
Imports System.Threading

Class MainWindow

    ' ***Declare a System.Threading.CancellationTokenSource.
    Dim cts As CancellationTokenSource

    Private Async Sub startButton_Click(sender As Object, e As RoutedEventArgs)
        ' ***Instantiate the CancellationTokenSource.
        cts = New CancellationTokenSource()

        resultsTextBox.Clear()

        Try
            ' ***Send a token to carry the message if cancellation is requested.
            Dim contentLength As Integer = Await AccessTheWebAsync(cts.Token)

            resultsTextBox.Text &=
                String.Format(vbCrLf & "Length of the downloaded string: {0}." & vbCrLf, contentLength)

            ' *** If cancellation is requested, an OperationCanceledException results.
        Catch ex As OperationCanceledException
            resultsTextBox.Text &= vbCrLf & "Download canceled." & vbCrLf

        Catch ex As Exception
            resultsTextBox.Text &= vbCrLf & "Download failed." & vbCrLf
        End Try

        ' ***Set the CancellationTokenSource to Nothing when the download is complete.
        cts = Nothing
    End Sub

    ' ***Add an event handler for the Cancel button.
    Private Sub cancelButton_Click(sender As Object, e As RoutedEventArgs)

        If cts IsNot Nothing Then
            cts.Cancel()
        End If
    End Sub

    ' ***Provide a parameter for the CancellationToken.
    Async Function AccessTheWebAsync(ct As CancellationToken) As Task(Of Integer)

        Dim client As HttpClient = New HttpClient()

        resultsTextBox.Text &=
            String.Format(vbCrLf & "Ready to download." & vbCrLf)

        ' You might need to slow things down to have a chance to cancel.
        Await Task.Delay(250)

        ' GetAsync returns a Task(Of HttpResponseMessage). 
        ' ***The ct argument carries the message if the Cancel button is chosen.
        Dim response As HttpResponseMessage = Await client.GetAsync("https://msdn.microsoft.com/en-us/library/dd470362.aspx", ct)

        ' Retrieve the website contents from the HttpResponseMessage.
        Dim urlContents As Byte() = Await response.Content.ReadAsByteArrayAsync()

        ' The result of the method is the length of the downloaded website.
        Return urlContents.Length
    End Function
End Class


' Output for a successful download:

' Ready to download.

' Length of the downloaded string: 158125.


' Or, if you cancel:

' Ready to download.

' Download canceled.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

// Add a using directive and a reference for System.Net.Http.
using System.Net.Http;

// Add the following using directive for System.Threading.

using System.Threading;
namespace CancelATask
{
    public partial class MainWindow : Window
    {
        // ***Declare a System.Threading.CancellationTokenSource.
        CancellationTokenSource cts;

        public MainWindow()
        {
            InitializeComponent();
        }


        private async void startButton_Click(object sender, RoutedEventArgs e)
        {
            // ***Instantiate the CancellationTokenSource.
            cts = new CancellationTokenSource();

            resultsTextBox.Clear();

            try
            {
                // ***Send a token to carry the message if cancellation is requested.
                int contentLength = await AccessTheWebAsync(cts.Token);
                resultsTextBox.Text +=
                    String.Format("\r\nLength of the downloaded string: {0}.\r\n", contentLength);
            }
            // *** If cancellation is requested, an OperationCanceledException results.
            catch (OperationCanceledException)
            {
                resultsTextBox.Text += "\r\nDownload canceled.\r\n";
            }
            catch (Exception)
            {
                resultsTextBox.Text += "\r\nDownload failed.\r\n";
            }

            // ***Set the CancellationTokenSource to null when the download is complete.
            cts = null; 
        }


        // ***Add an event handler for the Cancel button.
        private void cancelButton_Click(object sender, RoutedEventArgs e)
        {
            if (cts != null)
            {
                cts.Cancel();
            }
        }


        // ***Provide a parameter for the CancellationToken.
        async Task<int> AccessTheWebAsync(CancellationToken ct)
        {
            HttpClient client = new HttpClient();

            resultsTextBox.Text +=
                String.Format("\r\nReady to download.\r\n");

            // You might need to slow things down to have a chance to cancel.
            await Task.Delay(250);

            // GetAsync returns a Task<HttpResponseMessage>. 
            // ***The ct argument carries the message if the Cancel button is chosen.
            HttpResponseMessage response = await client.GetAsync("https://msdn.microsoft.com/en-us/library/dd470362.aspx", ct);

            // Retrieve the website contents from the HttpResponseMessage.
            byte[] urlContents = await response.Content.ReadAsByteArrayAsync();

            // The result of the method is the length of the downloaded website.
            return urlContents.Length;
        }
    }

    // Output for a successful download:

    // Ready to download.

    // Length of the downloaded string: 158125.


    // Or, if you cancel:

    // Ready to download.

    // Download canceled.
}

取消工作範例清單。

下列程式碼完成 MainWindow.xaml.vb 或取消工作清單的範例的 MainWindow.xaml.cs 檔案。

' Add an Imports directive and a reference for System.Net.Http.
Imports System.Net.Http

' Add the following Imports directive for System.Threading.
Imports System.Threading

Class MainWindow

    ' Declare a System.Threading.CancellationTokenSource.
    Dim cts As CancellationTokenSource


    Private Async Sub startButton_Click(sender As Object, e As RoutedEventArgs)

        ' Instantiate the CancellationTokenSource.
        cts = New CancellationTokenSource()

        resultsTextBox.Clear()

        Try
            ' ***AccessTheWebAsync returns a Task, not a Task(Of Integer).
            Await AccessTheWebAsync(cts.Token)
            '  ***Small change in the display lines.
            resultsTextBox.Text &= vbCrLf & "Downloads complete."

        Catch ex As OperationCanceledException
            resultsTextBox.Text &= vbCrLf & "Downloads canceled." & vbCrLf

        Catch ex As Exception
            resultsTextBox.Text &= vbCrLf & "Downloads failed." & vbCrLf
        End Try

        ' Set the CancellationTokenSource to Nothing when the download is complete.
        cts = Nothing
    End Sub


    ' Add an event handler for the Cancel button.
    Private Sub cancelButton_Click(sender As Object, e As RoutedEventArgs)

        If cts IsNot Nothing Then
            cts.Cancel()
        End If
    End Sub


    ' Provide a parameter for the CancellationToken.
    ' ***Change the return type to Task because the method has no return statement.
    Async Function AccessTheWebAsync(ct As CancellationToken) As Task

        Dim client As HttpClient = New HttpClient()

        ' ***Call SetUpURLList to make a list of web addresses.
        Dim urlList As List(Of String) = SetUpURLList()

        ' ***Add a loop to process the list of web addresses.
        For Each url In urlList
            ' GetAsync returns a Task(Of HttpResponseMessage). 
            ' Argument ct carries the message if the Cancel button is chosen. 
            ' ***Note that the Cancel button can cancel all remaining downloads.
            Dim response As HttpResponseMessage = Await client.GetAsync(url, ct)

            ' Retrieve the website contents from the HttpResponseMessage.
            Dim urlContents As Byte() = Await response.Content.ReadAsByteArrayAsync()

            resultsTextBox.Text &=
                String.Format(vbCrLf & "Length of the downloaded string: {0}." & vbCrLf, urlContents.Length)
        Next
    End Function


    ' ***Add a method that creates a list of web addresses.
    Private Function SetUpURLList() As List(Of String)

        Dim urls = New List(Of String) From
            {
                "https://msdn.microsoft.com",
                "https://msdn.microsoft.com/en-us/library/hh290138.aspx",
                "https://msdn.microsoft.com/en-us/library/hh290140.aspx",
                "https://msdn.microsoft.com/en-us/library/dd470362.aspx",
                "https://msdn.microsoft.com/en-us/library/aa578028.aspx",
                "https://msdn.microsoft.com/en-us/library/ms404677.aspx",
                "https://msdn.microsoft.com/en-us/library/ff730837.aspx"
            }
        Return urls
    End Function

End Class


' Output if you do not choose to cancel:

' Length of the downloaded string: 35939.

' Length of the downloaded string: 237682.

' Length of the downloaded string: 128607.

' Length of the downloaded string: 158124.

' Length of the downloaded string: 204890.

' Length of the downloaded string: 175488.

' Length of the downloaded string: 145790.

' Downloads complete.


'  Sample output if you choose to cancel:

' Length of the downloaded string: 35939.

' Length of the downloaded string: 237682.

' Length of the downloaded string: 128607.

' Downloads canceled.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

// Add a using directive and a reference for System.Net.Http.
using System.Net.Http;

// Add the following using directive for System.Threading.
using System.Threading;

namespace CancelAListOfTasks
{
    public partial class MainWindow : Window
    {
        // Declare a System.Threading.CancellationTokenSource.
        CancellationTokenSource cts;

        public MainWindow()
        {
            InitializeComponent();
        }


        private async void startButton_Click(object sender, RoutedEventArgs e)
        {
            // Instantiate the CancellationTokenSource.
            cts = new CancellationTokenSource();

            resultsTextBox.Clear();

            try
            {
                await AccessTheWebAsync(cts.Token);
                // ***Small change in the display lines.
                resultsTextBox.Text += "\r\nDownloads complete.";
            }
            catch (OperationCanceledException)
            {
                resultsTextBox.Text += "\r\nDownloads canceled.";
            }
            catch (Exception)
            {
                resultsTextBox.Text += "\r\nDownloads failed.";
            }

            // Set the CancellationTokenSource to null when the download is complete.
            cts = null;
        }


        // Add an event handler for the Cancel button.
        private void cancelButton_Click(object sender, RoutedEventArgs e)
        {
            if (cts != null)
            {
                cts.Cancel();
            }
        }


        // Provide a parameter for the CancellationToken.
        // ***Change the return type to Task because the method has no return statement.
        async Task AccessTheWebAsync(CancellationToken ct)
        {
            // Declare an HttpClient object.
            HttpClient client = new HttpClient();

            // ***Call SetUpURLList to make a list of web addresses.
            List<string> urlList = SetUpURLList();

            // ***Add a loop to process the list of web addresses.
            foreach (var url in urlList)
            {
                // GetAsync returns a Task<HttpResponseMessage>. 
                // Argument ct carries the message if the Cancel button is chosen. 
                // ***Note that the Cancel button can cancel all remaining downloads.
                HttpResponseMessage response = await client.GetAsync(url, ct);

                // Retrieve the website contents from the HttpResponseMessage.
                byte[] urlContents = await response.Content.ReadAsByteArrayAsync();

                resultsTextBox.Text +=
                    String.Format("\r\nLength of the downloaded string: {0}.\r\n", urlContents.Length);
            }
        }


        // ***Add a method that creates a list of web addresses.
        private List<string> SetUpURLList()
        {
            List<string> urls = new List<string> 
            { 
                "https://msdn.microsoft.com",
                "https://msdn.microsoft.com/en-us/library/hh290138.aspx",
                "https://msdn.microsoft.com/en-us/library/hh290140.aspx",
                "https://msdn.microsoft.com/en-us/library/dd470362.aspx",
                "https://msdn.microsoft.com/en-us/library/aa578028.aspx",
                "https://msdn.microsoft.com/en-us/library/ms404677.aspx",
                "https://msdn.microsoft.com/en-us/library/ff730837.aspx"
            };
            return urls;
        }
    }

    // Output if you do not choose to cancel:

    //Length of the downloaded string: 35939.

    //Length of the downloaded string: 237682.

    //Length of the downloaded string: 128607.

    //Length of the downloaded string: 158124.

    //Length of the downloaded string: 204890.

    //Length of the downloaded string: 175488.

    //Length of the downloaded string: 145790.

    //Downloads complete.


    // Sample output if you choose to cancel:

    //Length of the downloaded string: 35939.

    //Length of the downloaded string: 237682.

    //Length of the downloaded string: 128607.

    //Downloads canceled.
}

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