C#通過“委托和事件”的方式實現進程監控並與“普通方式”對比

今天重新學習了一下觀察者模式，對我的思路產生了啟發。進程監控程序之前寫過幾個，這回換一種思路，改用委托和事件來實現。我已經用序號將關鍵的幾步標注，方便大家理順思路。代碼如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ProcessMonitor
{
    public partial class ProcessMonitorForm : Form
    {
        public ProcessMonitorForm()
        {
            InitializeComponent();
            //Add the processes into the combox.
            var processes = Process.GetProcesses();
            foreach (var process in processes)
            {
                processComboBox.Items.Add(process.ProcessName.ToString());
            }
        }
        //The method that starts the monitor.
        private void startButton_Click(object sender, EventArgs e)
        {
            //4.Register the monitor.
            ProcessExit += new ProcessMonitor(ProExit);
            //Start the check.
            CheckProcess();
        }
        //The mothod that checks the process.
        private void CheckProcess()
        {
            bool flag = true;
            do
            {
                var processes = Process.GetProcesses();
                int count = 0;
                foreach (var process in processes)
                {
                    if (string.Compare(process.ProcessName, processComboBox.Text, true) == 0)
                    {
                        count++;
                    }
                }
                if (count == 0)
                {
                    //5.The event appears.
                    ProcessExit(this, new EventArgs());
                    flag = false;
                }
            } while (flag);
        }
        //1.The delegate that monitor the process.
        public delegate void ProcessMonitor(object sender, EventArgs strEventArg);
        //2.The event that encapsulates the delegate.
        public event ProcessMonitor ProcessExit;
        //3.The method that the delegate calls.
        private void ProExit(object sender, EventArgs strEventArg)
        {
            MessageBox.Show("The target process has been dispeared.");
        }
    }
}

為了不長篇累牘，效果只是簡單實現，實際工作中可以隨便擴展（選擇進程，點擊Start按鈕進行監控。）：

目標程序消失后彈出提示：

再附上一個脫去委托和事件的版本，代碼如下（實現效果相同）：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ProcessMonitor
{
    public partial class ProcessMonitorForm : Form
    {
        public ProcessMonitorForm()
        {
            InitializeComponent();
            //Add the processes into the combox.
            var processes = Process.GetProcesses();
            foreach (var process in processes)
            {
                processComboBox.Items.Add(process.ProcessName.ToString());
            }
        }
        //The method that starts the monitor.
        private void startButton_Click(object sender, EventArgs e)
        {
            //Start the check.
            CheckProcess();
        }
        //The mothod that checks the process.
        private void CheckProcess()
        {
            bool flag = true;
            do
            {
                var processes = Process.GetProcesses();
                int count = 0;
                foreach (var process in processes)
                {
                    if (string.Compare(process.ProcessName, processComboBox.Text, true) == 0)
                    {
                        count++;
                    }
                }
                if (count == 0)
                {
                    ProExit();
                    flag = false;
                }
            } while (flag);
        }
        private void ProExit()
        {
            MessageBox.Show("The target process has been dispeared.");
        }
    }
}

如果用Action內置委托類型來完成的話就更方便了，代碼如下（已經用序號標注關鍵步驟）：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ProcessMonitor
{
    public partial class ProcessMonitorForm : Form
    {
        public ProcessMonitorForm()
        {
            InitializeComponent();
            //Add the processes into the combox.
            var processes = Process.GetProcesses();
            foreach (var process in processes)
            {
                processComboBox.Items.Add(process.ProcessName.ToString());
            }
        }
        //The method that starts the monitor.
        private void startButton_Click(object sender, EventArgs e)
        {
            //Start the check.
            CheckProcess();
        }
        //The mothod that checks the process.
        private void CheckProcess()
        {
            //1.Define the action.
            Action<string> processExit = s => MessageBox.Show(s);
            bool flag = true;
            do
            {
                var processes = Process.GetProcesses();
                int count = 0;
                foreach (var process in processes)
                {
                    if (string.Compare(process.ProcessName, processComboBox.Text, true) == 0)
                    {
                        count++;
                    }
                }
                if (count == 0)
                {
                    //2.Active the action.
                    processExit("The target process has been dispeared.");
                    flag = false;
                }
            } while (flag);
        }
    }
}

脫去委托和事件的版本代碼量明顯比用委托和事件的代碼量少了，為什么我們還要選擇用委托和事件來做這件事呢？到底什么情況下，更適合用委托和事件的方式來完成？書中說，委托可以提高方法擴展性，沒錯，是這樣的，說白了就是因為更高級！個人意見哈，在代碼量少，以后不需要擴展方法的情況下，用不着用委托和事件的方式去完成，直接調用方法就好了。如果我說錯了，歡迎指正我。

利用C#6.0中的語法糖擴展方法來替代foreach循環，代碼量將更少。代碼如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ProcessMonitor
{
    public partial class ProcessMonitorForm : Form
    {
        public ProcessMonitorForm()
        {
            InitializeComponent();
            //Add the processes into the combox.
            var processes = Process.GetProcesses();
            foreach (var process in processes)
            {
                processComboBox.Items.Add(process.ProcessName.ToString());
            }
        }
        //The method that starts the monitor.
        private void startButton_Click(object sender, EventArgs e)
        {
            //Start the check.
            CheckProcess();
        }
        //The mothod that checks the process.
        private void CheckProcess()
        {
            //1.Define the action.
            Action<string> processExit = s => MessageBox.Show(s);
            bool flag = true;
            do
            {
                var processes = Process.GetProcesses();
                var countVar = processes.Where(i => i.ProcessName == processComboBox.Text);
                if (countVar.Count() == 0)
                {
                    //2.Active the action.
                    processExit("The target process has been dispeared.");
                    flag = false;
                }
            } while (flag);
        }
    }
}