Delegate Lambda Action Func-白红宇

Delegate Lambda Action Func

阅读量：6038 次

发布时间：2019-06-20

本文共 11237 字，大约阅读时间需要 37 分钟。

委托(Delegate)就是把方法(方法名)作为方法的参数，例如：

using System;using System.Collections.Generic;using System.Text;namespace TestDemo{    public delegate void Delegate(int arg);    class Program    {        private static void FunctionX2(int x)        {            Console.WriteLine(x*x);        }        private static void FunctionX3(int x)        {            Console.WriteLine(x*x*x);        }        private static void Action(int x, Delegate function)        {            function(x);        }        static void Main(string[] args)        {            Action(2, FunctionX2);            Action(2, FunctionX3);            Console.ReadKey();        }    }}

委托可以简化代码，但是更大的意义是在一个线程中调用另一个线程的代码，先来看一个程序。

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;namespace WinFormTest{    public partial class MainForm : Form    {        public MainForm()        {            InitializeComponent();        }        private void Print(int n)        {            for (int i = 1; i <= n; i++)            {                Output.AppendText(i.ToString() + Environment.NewLine);            }        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            int n = int.Parse(Input.Text);            Print(n);            Show.Enabled = true;        }    }}

当输入100的时候，显示框能迅速显示，1000的时候显示开始出现停顿，10000的时候，主窗口明显会卡住，直到输出完成。怎么样让界面不被卡住呢？答案就是用多线程。

以下就是经过多线程改进的代码。

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private int n;                public MainForm()        {            InitializeComponent();        }        private void Print()        {            for (int i = 1; i <= n; i++)            {                Output.AppendText(i.ToString() + Environment.NewLine);            }        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

运行时出现如下错误

在子线程中无法访问UI线程的对象，这个时候代理就该出场了。以下是用代理实现后的代码

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private delegate void UiAction(string text);        private int n;        public MainForm()        {            InitializeComponent();        }        private void Print()        {            UiAction uiAction = new UiAction(AppendText);            for (int i = 1; i <= n; i++)            {                Output.Invoke(uiAction, i.ToString() + Environment.NewLine);            }        }        private void AppendText(string text)        {            Output.AppendText(text);        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

运行之后，即使是10000，Output的Text在不停的变化，主界面仍然处于活动状态，可以拖动或执行其他操作。再来看一下代码的另一种形式

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private delegate void UiAction(string text);        private int n;        public MainForm()        {            InitializeComponent();        }        private void Print()        {            UiAction uiAction = new UiAction(delegate(string text) { Output.AppendText(text); });            for (int i = 1; i <= n; i++)            {                Output.Invoke(uiAction, i.ToString() + Environment.NewLine);            }        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

执行正常，这是匿名委托的写法，匿名委托还可写成这样

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private delegate void UiAction();        private int n;        public MainForm()        {            InitializeComponent();        }        private void Print()        {            for (int i = 1; i <= n; i++)            {                Output.Invoke(new UiAction(delegate() { Output.AppendText(i.ToString() + Environment.NewLine); }));            }        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

现在我们再来引入一个概念Action，先看代码

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private int n;        public MainForm()        {            InitializeComponent();        }        private void Print()        {            for (int i = 1; i <= n; i++)            {                Action
     
       action = AppendText;                Output.Invoke(action, i.ToString() + Environment.NewLine);            }        }        private void AppendText(string text)        {            Output.AppendText(text);        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

Action其实就是委托，Action不带返回，但是可以带参数(形如Action,Action<T>,Action<T1,T2>,Action<T1,T2,T3>,Action<T1,T2,T3,T4>),如果用Lambda表达式来写的话代码就应该是这样

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private int n;        public MainForm()        {            InitializeComponent();        }        private void Print()        {            for (int i = 1; i <= n; i++)            {                Output.Invoke(new Action
     
      ((string text) => Output.AppendText(text)), i.ToString() + Environment.NewLine);            }        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

也可以写成这样的无参形式

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        private int n;        public MainForm()        {            InitializeComponent();        }        private void Print()        {            for (int i = 1; i <= n; i++)            {                Output.Invoke(new Action(() => Output.AppendText(i.ToString() + Environment.NewLine)));            }        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            n = int.Parse(Input.Text);            new Thread(new ThreadStart(Print)).Start();            Show.Enabled = true;        }    }}

如果把线程代码也用Lambda形式表达，代码应为这样

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        public MainForm()        {            InitializeComponent();        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            new Thread(() =>{                for (int i = 1; i <= int.Parse(Input.Text); i++)                {                    Output.Invoke(new Action(() => Output.AppendText(i.ToString() + Environment.NewLine)));                }            }).Start();            Show.Enabled = true;        }    }}

相比上一种形式，上面这段代码连参数n都省略了，个人认为，Action配上Lambda可以巧妙的把一段实际执行的代码作为类似‘参数’的形式直接执行，这里还稍微引述一个问多线程的问题，如果代码写成这样

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        public MainForm()        {            InitializeComponent();        }        private void Show_Click(object sender, EventArgs e)        {            Show.Enabled = false;            Output.Text = "";            new Thread(() =>{                Output.Invoke(new Action(() => {                    for (int i = 1; i <= int.Parse(Input.Text); i++)                    {                        Output.AppendText(i.ToString() + Environment.NewLine);                    }                }));            }).Start();            Show.Enabled = true;        }    }}

执行结果会是主界面会卡住，原因就是‘10000次操作’作为线程的‘1次操作’在主界面线程上执行了，而invoke到主界面线程执行的时候是会占用主线程的执行时间的，这样的写法跟没有用线程差不多，小区别就是用线程的时候Show.Enabled = true代码能马上执行。

Func跟Action类似，不过Func可以带返回，如

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Threading;namespace WinFormTest{    public partial class MainForm : Form    {        public MainForm()        {            InitializeComponent();        }        private void Show_Click(object sender, EventArgs e)        {            Output.AppendText(DoSomething(new Func
     
      ((int n) => n * n)));            Output.AppendText(DoSomething(new Func
      
       ((int n) => n * n * n)));        }        private string DoSomething(Func
       
         func)        {            int n = int.Parse(Input.Text);            if (n % 2 == 0)            {                return "您输入的是偶数，执行结果为：" + func(n) + Environment.NewLine;            }            else            {                return "您输入的是奇数，执行结果为：" + func(n) + Environment.NewLine;            }        }    }}

转载于:https://www.cnblogs.com/bady1211/archive/2012/09/27/2706101.html

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