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C#使用Lambda表达式简化代码的示例详解

dawn 人气:0

Lambda,希腊字母λ,在C#编程语言中,被引入为Lambda表达式,表示为匿名函数(匿名方法)。

编程时离不开函数,函数都有函数名和函数体,声明函数名是为了方便多次使用,可是很多时候函数只使用一次,那么函数名就变得多余,这样就产生了匿名函数(匿名方法)。

很多编程语言都有Lambde表达式,如Python、JavaScript、Java等等,这似乎是现代编程语言的标配了。

作为编程语言C#和编程环境Visual Stuidio的发展,总得不停地变幻出新花样,功能还是那个功能或者略有增强,得益于编译器的强大,C#3.0推出了Lambda表达式。

其实这些是非必要的,只是为C#编码增加一些色彩和亮点而已,但是别人总喜欢这么写,我们就得熟悉这些规则了。

举例1:计算两个整数的相加和相减。

①  一般写法

        //声明变量
        private delegate int calculate(int x, int y);//声明一个用于计算的委托类型
        private calculate MyCalculate;//声明一个委托实例
 
        //声明函数
        private int Add(int x, int y)
        {
            return x+y;
        }
 
        private int Reduce(int x, int y)
        {
            return x - y;
        }

就可以直接使用了。

            MyCalculate = new calculate(Add);
            string StrResultAdd = MyCalculate(7, 2).ToString();
            MyCalculate = new calculate(Reduce);
            string StrResultReduce = MyCalculate(7, 2).ToString();
            //
            textBox1.Text = $"两数相加结果:{StrResultAdd}" + Environment.NewLine;
            textBox1.Text = textBox1.Text+ $"两数相减结果:{StrResultReduce}" + Environment.NewLine;

② 使用自定义的委托

使用自定义的委托来使用Lamda可以让代码更简洁:

            MyCalculate = delegate(int x,int y)
            {
                return x + y;
            };
            textBox1.Text = textBox1.Text+"两数相加结果:" + MyCalculate(7, 2).ToString()+Environment.NewLine;
            MyCalculate = delegate (int x, int y)
            {
                return x - y;
            };
            textBox1.Text = textBox1.Text + "两数相减结果:" + MyCalculate(7, 2).ToString() + Environment.NewLine;

上面得到的结果是一样的。

③ 使用Func委托

FUNC委托的重载:

Func<TResult>;
Func<T1,T2,TResult>;
Func<T1,...,T16,TResult>;

使用系统内置的FUNC命名的委托来写LambDa表达式:

Func<int,int,int> MyAdd = (int x, int y) => { return x + y; };
Func<int, int, int> MyReduce = (int x, int y) => { return x - y; };
 
textBox1.Text = textBox1.Text + $"两数相加结果:{MyAdd(7,2).ToString()}" + Environment.NewLine;
textBox1.Text = textBox1.Text + $"两数相减结果:{MyReduce(7, 2).ToString()}" + Environment.NewLine;

④ 使用规范的Lambda表达式

更简洁的写法:

MyCalculate = (int x, int y) => { return x + y; };
textBox1.Text = textBox1.Text+$"两数相加结果:{MyCalculate(7, 2).ToString()}" + Environment.NewLine;
MyCalculate = (int x, int y) => { return x - y; };
textBox1.Text = textBox1.Text+$"两数相减结果:{MyCalculate(7, 2).ToString()}" + Environment.NewLine;

完整代码:

namespace Lambda
{
    public partial class Form1 : Form
    {
        private delegate int calculate(int x, int y);//声明一个用于计算的委托类型
        private calculate MyCalculate;//声明一个委托实例
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            //1
            MyCalculate = new calculate(Add);
            string StrResultAdd = MyCalculate(7, 2).ToString();
            MyCalculate = new calculate(Reduce);
            string StrResultReduce = MyCalculate(7, 2).ToString();
            textBox1.Text = $"两数相加结果:{StrResultAdd}" + Environment.NewLine;
            textBox1.Text = textBox1.Text+ $"两数相减结果:{StrResultReduce}" + Environment.NewLine;
            //2
            MyCalculate = delegate(int x,int y)
            {
                return x + y;
            };
            textBox1.Text = textBox1.Text+"两数相加结果:" + MyCalculate(7, 2).ToString()+Environment.NewLine;
            MyCalculate = delegate (int x, int y)
            {
                return x - y;
            };
            textBox1.Text = textBox1.Text + "两数相减结果:" + MyCalculate(7, 2).ToString() + Environment.NewLine;
            //3
            Func<int,int,int> MyAdd = (int x, int y) => { return x + y; };
            Func<int, int, int> MyReduce = (int x, int y) => { return x - y; };
            textBox1.Text = textBox1.Text + $"两数相加结果:{MyAdd(7,2).ToString()}" + Environment.NewLine;
            textBox1.Text = textBox1.Text + $"两数相减结果:{MyReduce(7, 2).ToString()}" + Environment.NewLine;
            //4
            MyCalculate = (int x, int y) => { return x + y; };
            textBox1.Text = textBox1.Text+$"两数相加结果:{MyCalculate(7, 2).ToString()}" + Environment.NewLine;
            MyCalculate = (int x, int y) => { return x - y; };
            textBox1.Text = textBox1.Text+$"两数相减结果:{MyCalculate(7, 2).ToString()}" + Environment.NewLine;
        }
 
        private int Add(int x, int y)
        {
            return x+y;
        }
 
        private int Reduce(int x, int y)
        {
            return x - y;
        }

结果显示:

上面通过对比说明了Lambda表达式的应用,可以看出这样的写法相比传统的写法还是干净利落,的确简洁而优雅一些。   

上面的可以改写:

        private delegate int calculate1(int x, int y,string str);//声明一个用于计算的委托类型
        private calculate1 MyCalculate1;//声明一个委托实例
        MyCalculate1 = (int x, int y,string StrOP) => {
                switch (StrOP)
                {
                    case "+":
                        return x + y; break;
                    case "-": return x - y; break;
                    default: return 0; break;
                }
        };
        textBox1.Text = textBox1.Text + $"两数相加结果:{MyCalculate1(7, 2,"+").ToString()}" + Environment.NewLine;
        textBox1.Text = textBox1.Text + $"两数相减结果:{MyCalculate1(7, 2,"-").ToString()}" + Environment.NewLine;

或者:

            Func<int, int, string,int> MyOperate = (int x, int y, string StrOP) => {
                switch (StrOP)
                {
                    case "+":
                        return x + y; break;
                    case "-": return x - y; break;
                    default: return 0;break;
                    }
            };
            textBox1.Text = textBox1.Text + $"两数相加结果:{MyOperate(7, 2,"+").ToString()}" + Environment.NewLine;
            textBox1.Text = textBox1.Text + $"两数相减结果:{MyOperate(7, 2,"-").ToString()}" + Environment.NewLine;

从上面的代码演示中可以看出,Lambda与委托是紧密相连的。

举例2:求几个数的最大值与最小值。

① 一般写法:

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text += "最大值:"+GetMax(new int[6]{7, 11,23,4,15,6}).ToString();
            textBox1.Text += Environment.NewLine;
            textBox1.Text += "最小值:" + GetMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
        }
 
        private static int GetMax(int[] Arr)
        {
            int ReturnValue = Arr[0];
            foreach( int a in Arr)
            {
                if(a > ReturnValue) ReturnValue = a;
            }
 
            return ReturnValue;
        }
 
        private static int GetMin(int[] Arr)
        {
            int ReturnValue = Arr[0];
            foreach (int a in Arr)
            {
                if (a < ReturnValue) ReturnValue = a;
            }
            return ReturnValue;
        }

② 使用委托来改写:

        //声明委托
        private delegate int GetMaxOrMin(int[] Arr);
        private GetMaxOrMin MyGetMaxOrMin;
 
        //定义函数
        private static int GetMax(int[] Arr)
        {
            int ReturnValue = Arr[0];
            foreach( int a in Arr)
            {
                if(a > ReturnValue) ReturnValue = a;
            }
 
            return ReturnValue;
        }
 
        private static int GetMin(int[] Arr)
        {
            int ReturnValue = Arr[0];
            foreach (int a in Arr)
            {
                if (a < ReturnValue) ReturnValue = a;
            }
            return ReturnValue;
        }
        
        //使用
        private void button2_Click(object sender, EventArgs e)
        {
            MyGetMaxOrMin = new GetMaxOrMin( GetMax);
            textBox1.Text += "最大值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
            textBox1.Text += Environment.NewLine;
            MyGetMaxOrMin = new GetMaxOrMin(GetMin);
            textBox1.Text += "最小值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
        }

③ 使用自定义的委托

            MyGetMaxOrMin=delegate(int[] Arr)
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (a > ReturnValue) ReturnValue = a;
                }
 
                return ReturnValue;
            };
            textBox1.Text += "最大值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
            MyGetMaxOrMin = delegate (int[] Arr)
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (a < ReturnValue) ReturnValue = a;
                }
                return ReturnValue;
            };
            textBox1.Text += "最小值:" + GetMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();

到这里,我们看到这两个方法只是判断位置的代码略有不同,其他的都相同,那么这个地方就可以使用委托来代替,就是把判断方法当做参数传进去。

        private delegate Boolean Judge(int x,int y);//定义判断
        private Judge MyJudge;//实例化委托
 
        private delegate int GetMaxOrMin(int[] Arr,Judge j);//定义得到最大值或者最小值的计算方法
        private GetMaxOrMin MyGetMaxOrMin;//实例化
 
        private void button2_Click(object sender, EventArgs e)
        {            
            MyGetMaxOrMin=delegate(int[] Arr,Judge MyJude)
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (MyJudge(a,ReturnValue)) ReturnValue = a;
                }
                return ReturnValue;
            };
            MyJudge = delegate (int x, int y) { return x > y; };
            textBox1.Text += "最大值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 },MyJudge).ToString();
            MyJudge = delegate (int x, int y) { return x < y; };
            textBox1.Text += "最小值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 },MyJudge).ToString();
        }

上面的写法的效果是一样的。

④ 使用Func委托

            Func<int[],Judge,int> MyGetMax = (int[] Arr,Judge MyJudge) => {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (MyJudge(a, ReturnValue)) ReturnValue = a;
                }
                return ReturnValue;
            };
            MyJudge = delegate (int x, int y) { return x > y; };
            textBox1.Text += "最大值:" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 },MyJudge).ToString();
            MyJudge = delegate (int x, int y) { return x < y; };
            textBox1.Text += "最小值:" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();

⑤ 使用更简洁的Lambda表达式

            var MyGetMaxOrMin1 = (int[] Arr,Judge J1 ) =>
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (J1(a, ReturnValue)) ReturnValue = a;
                }
                return ReturnValue;
            };
            Judge JudgeMax = (int x, int y) => { return x > y; };
            textBox1.Text += "最大值:" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMax).ToString();
            Judge JudgeMin = (int x, int y) => { return x < y; };
            textBox1.Text += "最小值:" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMin).ToString();

完整代码:

using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Security.Cryptography.X509Certificates;
 
namespace Lambda
{
    public partial class Form1 : Form
    {
        private delegate int calculate(int x, int y);//声明一个用于计算的委托类型
        private calculate MyCalculate;//声明一个委托实例
 
        private delegate int calculate1(int x, int y,string str);//声明一个用于计算的委托类型
        private calculate1 MyCalculate1;//声明一个委托实例
 
        private delegate Boolean Judge(int x,int y);
        private Judge MyJudge;
 
        private delegate int GetMaxOrMinA(int[] Arr);
        private GetMaxOrMinA MyGetMaxOrMinA;
 
        private delegate int GetMaxOrMin(int[] Arr,Judge j);
        private GetMaxOrMin MyGetMaxOrMin;
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text += "最大值:" + GetMax(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
            textBox1.Text += "最小值:" + GetMin(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
            textBox1.Text += Environment.NewLine +"=====" + Environment.NewLine;
 
            MyGetMaxOrMinA = new GetMaxOrMinA(GetMax);
            textBox1.Text += "最大值:" + MyGetMaxOrMinA(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
            MyGetMaxOrMinA = new GetMaxOrMinA(GetMin);
            textBox1.Text += "最小值:" + MyGetMaxOrMinA(new int[6] { 7, 11, 23, 4, 15, 6 }).ToString();
            textBox1.Text += Environment.NewLine + "=====" + Environment.NewLine;
 
            MyGetMaxOrMin = delegate (int[] Arr, Judge MyJude)
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (MyJudge(a, ReturnValue)) ReturnValue = a;
                }
                return ReturnValue;
            };
            MyJudge = delegate (int x, int y) { return x > y; };
            textBox1.Text += "最大值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();
            MyJudge = delegate (int x, int y) { return x < y; };
            textBox1.Text += "最小值:" + MyGetMaxOrMin(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();
            textBox1.Text += Environment.NewLine +"=====" + Environment.NewLine;
 
            Func<int[], Judge, int> MyGetMax = (int[] Arr, Judge MyJudge) =>
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (MyJudge(a, ReturnValue)) ReturnValue = a;
                }
                return ReturnValue;
            };
            MyJudge = delegate (int x, int y) { return x > y; };
            textBox1.Text += "最大值:" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();
            MyJudge = delegate (int x, int y) { return x < y; };
            textBox1.Text += "最小值:" + MyGetMax(new int[6] { 7, 11, 23, 4, 15, 6 }, MyJudge).ToString();
            textBox1.Text += Environment.NewLine +"=====" + Environment.NewLine;
 
            var MyGetMaxOrMin1 = (int[] Arr,Judge Judge1 ) =>
            {
                int ReturnValue = Arr[0];
                foreach (int a in Arr)
                {
                    if (Judge1(a, ReturnValue)) ReturnValue = a;
                }
                return ReturnValue;
            };
            Judge JudgeMax = (int x, int y) => { return x > y; };
            textBox1.Text += "最大值:" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMax).ToString();
            Judge JudgeMin = (int x, int y) => { return x < y; };
            textBox1.Text += "最小值:" + MyGetMaxOrMin1(new int[6] { 7, 11, 23, 4, 15, 6 }, JudgeMin).ToString();
 
        }
        private static int GetMax(int[] Arr)
        {
            int ReturnValue = Arr[0];
            foreach( int a in Arr)
            {
                if(a > ReturnValue) ReturnValue = a;
            }
 
            return ReturnValue;
        }
 
        private static int GetMin(int[] Arr)
        {
            int ReturnValue = Arr[0];
            foreach (int a in Arr)
            {
                if (a < ReturnValue) ReturnValue = a;
            }
            return ReturnValue;
        }
 
        private static List<int> GetEven(List<int> list)
        {
            List<int> ReturnList =new List<int>();
            foreach (var a in list)
            {
                if (a %2 == 0) ReturnList.Add(a);
            }
            return ReturnList;
        }
 
        private static List<int> GetOdd(List<int> list)
        {
            List<int> ReturnList = new List<int>();
            foreach (var a in list)
            {
                if ( (a+1) % 2 == 0) ReturnList.Add(a);
            }
            return ReturnList;
        }
 
    }
}

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