ASP.NET Learning Center---学习ASP.NET(1)

1,学习地址---微软官网

2,目标:学习Razor,以及建立Web应用.

3,https://docs.microsoft.com/zh-cn/aspnet/core/tutorials/razor-pages/?view=aspnetcore-3.0

4,概念学习:

异步编程模型 (TAP)'

相关网站

https://www.cnblogs.com/neverc/p/4653539.html

5, 异步线程执行的几个方式:

1,创建任务并且启动:

//方法1:
Task t = new Task(
               () =>
               {
                   Thread.Sleep(1000);
                   Console.WriteLine("Hello,World1\n");
               });
             t.Start();
//方法2:
await Task.Run(
             () =>
             {
                 Thread.Sleep(1000);
                 Console.WriteLine("Hello,World1\n");
             });

//方法3:

Task<string> task2 =Task.Factory.StartNew<string>(() =>
            {
                return $"hello, task2的ID为{ Thread.CurrentThread.ManagedThreadId}";
            });

2,aysnc 和 await的组合:

Thread.Sleep(1000);
             Console.WriteLine("Hello,World\n");
              await Task.Run<int>(
              () =>
              {
                  Thread.Sleep(1000);
                  Console.WriteLine("Hello,World1\n");
                  return 1;
              });
             Console.WriteLine("Hello,World2\n");
             return 1;

注意: 执行顺序     主函数---->调用aysnc函数并执行到await语句---------->回到主程序--->执行await之后的语句.

\                                                           /

\--执行 异步函数体-----------并且返回----/

3,任务的启动,取消,回调等...

任务等待:

Task的Wait/WaitAny/WaitAll方法
Task.WaitAll(new Task[]{ task1,task2});
Task.Factory.ContinueWhenAll(new Task[] { task1, task2 }, (t) =>
            {
                Thread.Sleep(100);
                Console.WriteLine("执行后续操作");
            });

4,任务取消CancellationTokenSource

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 +=
                    $"\r\nLength of the downloaded string: {urlContents.Length}.\r\n";
            }
        }

        // ***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/library/hh290138.aspx",
                "https://msdn.microsoft.com/library/hh290140.aspx",
                "https://msdn.microsoft.com/library/dd470362.aspx",
                "https://msdn.microsoft.com/library/aa578028.aspx",
                "https://msdn.microsoft.com/library/ms404677.aspx",
                "https://msdn.microsoft.com/library/ff730837.aspx"
            };
            return urls;
        }
    }

static async void GetWebAsync1(CancellationToken ct)
        {
            try
            {
                await AccessTheWebAsync(ct);

            }
            catch (OperationCanceledException)
            {

            }
            catch (Exception)
            {

            }

        }
    }

5 在一个任务完成后取消后续任务

static async Task  AccessTheWebAsync(CancellationTokenSource cts,CancellationToken ct)
        {
            HttpClient client = new HttpClient();
            List<string> urlList = SetUpURLList();
            IEnumerable<Task<int>> downloadTasksQuery =
                from url in urlList select ProcessURLAsync(url, client, ct);

            // ***Use ToArray to execute the query and start the download tasks.
            Task<int>[] downloadTasks = downloadTasksQuery.ToArray();

            // ***Call WhenAny and then await the result. The task that finishes
            // first is assigned to firstFinishedTask.
            Task<int> firstFinishedTask = await Task.WhenAny(downloadTasks);
            

cts.Cancel();

            // websites can finish first.
            var length = await firstFinishedTask;
            Console.WriteLine($"\r\nLength of the downloaded website:  {length}\r\n");
        }

5.1 利用 Linq语法生成枚举类型,然后再触发异步事件群.

5.2 利用WhenAny,WhenAll等方法进行堵塞

static async Task  AccessTheWebAsync(CancellationTokenSource cts,CancellationToken ct)
        {
            HttpClient client = new HttpClient();
            List<string> urlList = SetUpURLList();
            IEnumerable<Task<int>> downloadTasksQuery =
                from url in urlList select ProcessURLAsync(url, client, ct);

            // ***Use ToArray to execute the query and start the download tasks.
            Task<int>[] downloadTasks = downloadTasksQuery.ToArray();
           int[] first =await Task.WhenAll(downloadTasks);
            foreach(var x in first) Console.WriteLine(x + "\r\n");

        }
       static async Task<int> ProcessURLAsync(string url, HttpClient client, CancellationToken ct)
        {
            // GetAsync returns a Task<HttpResponseMessage>.
            HttpResponseMessage response = await client.GetAsync(url, ct);

            // Retrieve the website contents from the HttpResponseMessage.
            byte[] urlContents = await response.Content.ReadAsByteArrayAsync();
            Console.WriteLine("\r\n{urlContents}");
            return urlContents.Length;
        }

6,异步的防止再次进入函数的方法: