新建一個Winfrom專案，加入下面程式碼：

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 執行緒2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Task task1 = new Task(() =>
            {
                Thread.Sleep(400);
                Console.WriteLine("task1");
            });
            Task task2 = new Task(() =>
            {
                Thread.Sleep(300);
                Console.WriteLine("task2");
            });
            Task task3 = new Task(() =>
            {
                Thread.Sleep(200);
                Console.WriteLine("task3");
            });
            Task task4 = new Task(() =>
            {
                Thread.Sleep(100);
                Console.WriteLine("task4");
            });
            task1.Start();
            task2.Start();
            task3.Start();
            task4.Start();
        }
    }
}

執行：

由於延時不同，最先執行的Task1，反而最後一個執行完，那麼如果要求從任務1，一直執行到任務4，怎麼寫呢？

程式碼：

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 執行緒2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private List<Task> TaskList = new List<Task>();

        private void Form1_Load(object sender, EventArgs e)
        {
            Task task1 = new Task(() =>
            {
                Thread.Sleep(400);
                Console.WriteLine("task1");
            });
            Task task2 = new Task(() =>
            {
                Thread.Sleep(300);
                Console.WriteLine("task2");
            });
            Task task3 = new Task(() =>
            {
                Thread.Sleep(200);
                Console.WriteLine("task3");
            });
            Task task4 = new Task(() =>
            {
                Thread.Sleep(100);
                Console.WriteLine("task4");
            });

            TaskList.Add(task1);
            TaskList.Add(task2);
            TaskList.Add(task3);
            TaskList.Add(task4);

            foreach (Task task in TaskList)
            {
                task.Start();
                task.Wait();
            }
        }
    }
}

執行：

用上面的方法雖然有效，但會阻塞主執行緒，導致winfrom介面卡住，無法操作，那麼用異常的方法怎麼樣呢？

程式碼：

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 執行緒2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }


        private List<Task> TaskList = new List<Task>();

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void Button_Calculate_Click(object sender, EventArgs e)
        {
            Task task1 = new Task(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(4));
                Console.WriteLine("task1");
            });
            Task task2 = new Task(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(3));
                Console.WriteLine("task2");
            });
            Task task3 = new Task(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(2));
                Console.WriteLine("task3");
            });
            Task task4 = new Task(async () =>
            {
                await Task.Delay(TimeSpan.FromSeconds(1));
                Console.WriteLine("task4");
            });

            TaskList.Add(task1);
            TaskList.Add(task2);
            TaskList.Add(task3);
            TaskList.Add(task4);

            foreach (Task task in TaskList)
            {
                task.Start();
                task.Wait();
            }
        }
    }
}

執行：

用非同步方式雖然介面不會卡住，但另一個問題來了，task.wait()方法似乎沒有效果。裡面的任務佇列依然沒有按順序來執行。

後面我終於找到方法了，用下面的方法既不會卡住UI，也會按照佇列來執行，雖然寫法不是特別好，讀者可以按下面方法自己封裝了。

private void Test()
{
    Task.Run(() =>
    {
        Task t1 = new Task(() => {
            Thread.Sleep(2000);
            Console.WriteLine("t1");
            num = 1;
        });
        t1.Start();
        t1.Wait();
        Task t2 = new Task(() => {
            Thread.Sleep(1000);
            Console.WriteLine("t2");
            num = 3;
        });
        t2.Start();
        t2.Wait();
        Console.WriteLine("執行緒執行完畢");
    });
}

執行：

如果你這個帖子對你有用，歡迎給我點贊 + 留言，謝謝

end