C#语言各个版本特性(二)
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2022-05-07 15:57:19
二、排序Product 1.按名称对产品进行排序，以特定顺序显示一个列表的最简单方式就是先将列表排序，再遍历并显示其中的项。 C#1.1 使用IComparer对ArrayList进行排序 product类 1 using System.Collections; 2 using System.Com ......
二、排序Product
1.按名称对产品进行排序，以特定顺序显示一个列表的最简单方式就是先将列表排序，再遍历并显示其中的项。
C#1.1 使用IComparer对ArrayList进行排序
product类
1 using System.Collections;
2 using System.ComponentModel;
3
4 namespace Chapter01.CSharp1
5 {
6 [Description("Listing 1.01")]
7 public class Product
8 {
9 string name;
10 public string Name
11 {
12 get { return name; }
13 }
14
15 decimal price;
16 public decimal Price
17 {
18 get { return price; }
19 }
20
21 public Product(string name, decimal price)
22 {
23 this.name = name;
24 this.price = price;
25 }
26
27 public static ArrayList GetSampleProducts()
28 {
29 ArrayList list = new ArrayList();
30 list.Add(new Product("West Side Story", 9.99m));
31 list.Add(new Product("Assassins", 14.99m));
32 list.Add(new Product("Frogs", 13.99m));
33 list.Add(new Product("Sweeney Todd", 10.99m));
34 return list;
35 }
36
37 public override string ToString()
38 {
39 return string.Format("{0}: {1}", name, price);
40 }
41 }
42 }
ArrayListSort类
1 using System;
2 using System.Collections;
3 using System.ComponentModel;
4
5 namespace Chapter01.CSharp1
6 {
7 [Description("Listing 1.05")]
8 class ArrayListSort
9 {
10 class ProductNameComparer : IComparer
11 {
12 public int Compare(object x, object y)
13 {
14 Product first = (Product)x;
15 Product second = (Product)y;
16 return first.Name.CompareTo(second.Name);
17 }
18 }
19
20 static void Main()
21 {
22 ArrayList products = Product.GetSampleProducts();
23 products.Sort(new ProductNameComparer());
24 foreach (Product product in products)
25 {
26 Console.WriteLine(product);
27 }
28 }
29 }
30 }
提供一个IComparer实现，比较器。或者Product类实现IComparable。
区别：IComparer和IComparable(比较器接口和可比较的接口)
缺陷：Compare方法中显示强制类型转换，而ArrayList是类型不安全的，转换为对象Product时可能报错。foreach循环中隐式的编译器自动类型转换，转换为Product类型执行时可能报错。
2.C#2.0 引入泛型，使用IComparer<Product>对List<Product>进行排序
product类
1 using System.Collections.Generic;
2 using System.ComponentModel;
3
4 namespace Chapter01.CSharp2
5 {
6 [Description("Listing 1.02")]
7 public class Product
8 {
9 string name;
10 public string Name
11 {
12 get { return name; }
13 private set { name = value; }
14 }
15
16 decimal price;
17 public decimal Price
18 {
19 get { return price; }
20 private set { price = value; }
21 }
22
23 public Product(string name, decimal price)
24 {
25 Name = name;
26 Price = price;
27 }
28
29 public static List<Product> GetSampleProducts()
30 {
31 List<Product> list = new List<Product>();
32 list.Add(new Product("West Side Story", 9.99m));
33 list.Add(new Product("Assassins", 14.99m));
34 list.Add(new Product("Frogs", 13.99m));
35 list.Add(new Product("Sweeney Todd", 10.99m));
36 return list;
37 }
38
39 public override string ToString()
40 {
41 return string.Format("{0}: {1}", name, price);
42 }
43 }
44 }
ListSortWithComparer类
1 using System;
2 using System.Collections.Generic;
3 using System.ComponentModel;
4
5 namespace Chapter01.CSharp2
6 {
7 [Description("Listing 1.06")]
8 class ListSortWithComparer
9 {
10 class ProductNameComparer : IComparer<Product>
11 {
12 public int Compare(Product first, Product second)
13 {
14 return first.Name.CompareTo(second.Name);
15 }
16 }
17
18 static void Main()
19 {
20 List<Product> products = Product.GetSampleProducts();
21 products.Sort(new ProductNameComparer());
22 foreach (Product product in products)
23 {
24 Console.WriteLine(product);
25 }
26 }
27 }
28 }
使用Comparison<Product>对List<Product>进行排序(C#2)，不需要实现ProductNameComparer比较器类型，只是创建一个委托实例(C#2.0 匿名方法)。
1 using System;
2 using System.Collections.Generic;
3 using System.ComponentModel;
4
5 namespace Chapter01.CSharp2
6 {
7 [Description("Listing 1.07")]
8 class ListSortWithComparisonDelegate
9 {
10 static void Main()
11 {
12 List<Product> products = Product.GetSampleProducts();
13 products.Sort(delegate(Product first, Product second)
14 { return first.Name.CompareTo(second.Name); }
15 );
16 foreach (Product product in products)
17 {
18 Console.WriteLine(product);
19 }
20 }
21 }
22 }
3.C#3.0 Lambda表达式 在Lambda表达式中使用Comparison<Product>进行排序(C#3)
product类
1 using System.Collections.Generic;
2 using System.ComponentModel;
3
4 namespace Chapter01.CSharp3
5 {
6 [Description("Listing 1.3")]
7 class Product
8 {
9 public string Name { get; private set; }
10 public decimal Price { get; private set; }
11
12 public Product(string name, decimal price)
13 {
14 Name = name;
15 Price = price;
16 }
17
18 Product()
19 {
20 }
21
22 public static List<Product> GetSampleProducts()
23 {
24 return new List<Product>
25 {
26 new Product { Name="West Side Story", Price = 9.99m },
27 new Product { Name="Assassins", Price=14.99m },
28 new Product { Name="Frogs", Price=13.99m },
29 new Product { Name="Sweeney Todd", Price=10.99m}
30 };
31 }
32
33 public override string ToString()
34 {
35 return string.Format("{0}: {1}", Name, Price);
36 }
37 }
38 }
ListSortWithLambdaExpression类
1 using System;
2 using System.Collections.Generic;
3 using System.ComponentModel;
4
5 namespace Chapter01.CSharp3
6 {
7 [Description("Listing 1.08")]
8 class ListSortWithLambdaExpression
9 {
10 static void Main()
11 {
12 List<Product> products = Product.GetSampleProducts();
13 products.Sort(
14 (first, second) => first.Name.CompareTo(second.Name)
15 );
16 foreach (Product product in products)
17 {
18 Console.WriteLine(product);
19 }
20 }
21 }
22 }
ListOrderWithExtensionMethod类 使用扩展方法对List<Product>进行排序
1 using System;
2 using System.Collections.Generic;
3 using System.ComponentModel;
4 using System.Linq;
5
6 namespace Chapter01.CSharp3
7 {
8 [Description("Listing 1.09")]
9 class ListOrderWithExtensionMethod
10 {
11 static void Main()
12 {
13 List<Product> products = Product.GetSampleProducts();
14
15 foreach (Product product in products.OrderBy(p => p.Name))
16 {
17 Console.WriteLine(product);
18 }
19 }
20 }
21 }
总结：
→C#1,弱类型的比较功能不支持委托排序。
→C#2,强类型的比较功能，委托比较，匿名方法。
→C#3Lambda表达式，扩展方法,允许列表保持未排序状态。