C# in depth (第一章 C#开发的进化史）

1.1 [b]数据类型[/b]

C#1.0

[Description("Listing 1.01")]
public class Product
{
string name;
public string Name
{
get { return name; }
}

decimal price;
public decimal Price
{
get { return price; }
}

public Product(string name, decimal price)
{
this.name = name;
this.price = price;
}

public static ArrayList GetSampleProducts()
{
ArrayList list = new ArrayList();
list.Add(new Product("West Side Story", 9.99m));
list.Add(new Product("Assassins", 14.99m));
list.Add(new Product("Frogs", 13.99m));
list.Add(new Product("Sweeney Todd", 10.99m));
return list;
}

public override string ToString()
{
return string.Format("{0}: {1}", name, price);
}
}

ArrayList不是类型安全的

属性的Get和Set的Access只能一致

用于创建属性和变量的代码复杂（除属性外必须再声明一个变量)

C#2.0

public class Product
{
string name;
public string Name
{
get { return name; }
private set { name = value; }
}

decimal price;
public decimal Price
{
get { return price; }
private set { price = value; }
}

public Product(string name, decimal price)
{
Name = name;
Price = price;
}

public static List<Product> GetSampleProducts()
{
List<Product> list = new List<Product>();
list.Add(new Product("West Side Story", 9.99m));
list.Add(new Product("Assassins", 14.99m));
list.Add(new Product("Frogs", 13.99m));
list.Add(new Product("Sweeney Todd", 10.99m));
return list;
}

public override string ToString()
{
return string.Format("{0}: {1}", name, price);
}
}

解决了C#1.0 里三个问题的前两个，(泛型，Private Set)

C#3.0

class Product
{
public string Name { get; private set; }
public decimal Price { get; private set; }

public Product(string name, decimal price)
{
Name = name;
Price = price;
}

Product()
{
}

public static List<Product> GetSampleProducts()
{
return new List<Product>
{
new Product { Name="West Side Story", Price = 9.99m },
new Product { Name="Assassins", Price=14.99m },
new Product { Name="Frogs", Price=13.99m },
new Product { Name="Sweeney Todd", Price=10.99m}
};
}

public override string ToString()
{
return string.Format("{0}: {1}", Name, Price);
}
}

通过自动属性解决了C#1.0里的第三个问题。

C#4.0

public class Product
{
readonly string name;
public string Name { get { return name; } }

decimal? price;
public decimal? Price { get { return price; } }

public Product(string name, decimal? price = null)
{
this.name = name;
this.price = price;
}

public static List<Product> GetSampleProducts()
{
List<Product> list = new List<Product>();
list.Add(new Product(name: "West Side Story", price: 9.99m));
list.Add(new Product(name: "Assassins", price: 14.99m));
list.Add(new Product(name: "Frogs", price: 13.99m));
list.Add(new Product(name: "Sweeney Todd", price: 10.99m));
list.Add(new Product(name: "Unpriced"));
return list;
}

public override string ToString()
{
return string.Format("{0}: {1}", name, price);
}
}

命名实参带来了清晰的初始化代码。

1.2 [b]排序和过滤[/b]

1.2.1 按名称对产品进行排序

[b]C#1.0[/b]

class ArrayListSort
{
class ProductNameComparer : IComparer
{
public int Compare(object x, object y)
{
Product first = (Product)x;
Product second = (Product)y;
return first.Name.CompareTo(second.Name);
}
}

static void Main()
{
ArrayList products = Product.GetSampleProducts();
products.Sort(new ProductNameComparer());
foreach (Product product in products)
{
Console.WriteLine(product);
}
}
}

必须引入一个额外的类来进行排序

非类型安全的

C#2.0

class ListSortWithComparer
{
class ProductNameComparer : IComparer<Product>
{
public int Compare(Product first, Product second)
{
return first.Name.CompareTo(second.Name);
}
}

static void Main()
{
List<Product> products = Product.GetSampleProducts();
products.Sort(new ProductNameComparer());
foreach (Product product in products)
{
Console.WriteLine(product);
}
}
}

用以上方法排序，和C#1.0一样同样需要引入一个新的类，但是由于C#2.0支持泛型，解决了类型安全的问题。

class ListSortWithComparisonDelegate
{
static void Main()
{
List<Product> products = Product.GetSampleProducts();
products.Sort(delegate(Product first, Product second)
{ return first.Name.CompareTo(second.Name); }
);
foreach (Product product in products)
{
Console.WriteLine(product);
}
}
}
}

使用委托(Comparison)可以避免创建一个新的类(ProductNameComparer)，将创建的委托传给Sort方法来执行比较。（匿名方法）

C#3.0

class ListSortWithLambdaExpression
{
static void Main()
{
List<Product> products = Product.GetSampleProducts();
products.Sort(
(first, second) => first.Name.CompareTo(second.Name)
);
foreach (Product product in products)
{
Console.WriteLine(product);
}
}
}

使用兰巴达表达式来代替委托。

class ListOrderWithExtensionMethod
{
static void Main()
{
List<Product> products = Product.GetSampleProducts();

foreach (Product product in products.OrderBy(p => p.Name))
{
Console.WriteLine(product);
}
}
}

使用到了扩展方法(Orderby),允许列表保持未排序状态(products)本身没有排序。

1.2.2 查询集合

C#1.0

class ArrayListQuery
{
static void Main()
{
ArrayList products = Product.GetSampleProducts();
foreach (Product product in products)
{
if (product.Price > 10m)
{
Console.WriteLine(product);
}
}
}
}

用foreach循环，用if判断，再用Console.WritleLine显示产品，这三个任务的依赖性一目了然。

C#2.0

class ListQueryWithDelegates
{
static void Main()
{
List<Product> products = Product.GetSampleProducts();
Predicate<Product> test = delegate(Product p)
{ return p.Price > 10m; };
List<Product> matches = products.FindAll(test);

Action<Product> print = Console.WriteLine;
matches.ForEach(print);
}
}

class ListQueryWithDelegatesCompact
{
static void Main()
{
List<Product> products = Product.GetSampleProducts();
products.FindAll(delegate(Product p) { return p.Price > 10; })
.ForEach(delegate(Product p) { Console.WriteLine(p); });
}
}

测试和打印分开进行

C#3.0

class ListQueryWithLambdaExpression
{
static void Main()
{
List<Product> products = Product.GetSampleProducts();
foreach (Product product in products.Where(p => p.Price > 10))
{
Console.WriteLine(product);
}
}
}

使用兰巴达表达式

1.3处理未知数据 (Nullable<T>)

1.4Linq

1.5Com和动态类型(Dynamic)

1.6 async/await

private async void CheckProduct(object sender, EventArgs e)
{
try
{
// Only permit one lookup at a time
productCheckButton.Enabled = false;
statusLabel.Text = "Checking...";
nameValue.Text = "";
priceValue.Text = "";
stockValue.Text = "";

string id = idInput.Text;
Task<Product> productLookup =    directory.LookupProductAsync(id);
Task<int> stockLookup = warehouse.LookupStockLevelAsync(id);

Product product = await productLookup;
if (product == null)
{
statusLabel.Text = "Product not found";
// We don't care about the result of the stock check
return;
}
nameValue.Text = product.Name;
priceValue.Text = product.Price.ToString("c");

int stock = await stockLookup;
stockValue.Text = stock.ToString();
statusLabel.Text = "Ready";
}
finally
{
// However we finish this method, allow another lookup
productCheckButton.Enabled = true;
}
}