Item 1: 使用属性,避免可访问的数据成员  Use Properties Instead of Accessible Data Members

• 属性允许你创建一个想可访问数据的接口,而且仍然有使用方法的所有优点.Properties enable you to create an interface that acts like data access but still has all the benefits of a method.在.NET框架设计中数据绑定支持属性,而不是公共数据成员,在WPF,WF,WebForms,Silverlight中是一样的.In fact, the data binding classes in the .NET Framework support properties, not public data members. This is true for all the data binding libraries: WPF, Windows Forms, Web Forms, and Silverlight.
• textBoxCity.DataBindings.Add("Text",address, "City");
• 属性更易于更改,可以做校验或者额外的验证Properties are far easier to change as you discover new requirements or behaviors over time. You might soon decide that your customer type should never have a blank name. If you used a public property for Name, that’s easy to fix in one location
  1 public class Customer
  2 {
  3 private string name;
  4 public string Name
  5 {
  6 get { return name; }
  7 set
  8 {
  9 if (string.IsNullOrEmpty(value))
  10 throw new ArgumentException( "Name cannot be blank", "Name");
  11 name = value;
  12 }
  13 }
  14 }
• 因为属性里可以使用方法,因此添加多线程变得更加容易.Because properties are implemented with methods, adding multithreaded support is easier. You can enhance the implementation of the get and set accessors to provide synchronized access to the data:
  1 public class Customer
  2 {
  3 private object syncHandle = new object();
  4 private string name;
  5 public string Name
  6 {
  7 get
  8 {
  9 lock (syncHandle)
  10 return name;
  11 }
  12 set
  13 {
  14 if (string.IsNullOrEmpty(value))
  15 throw new ArgumentException("Name cannot be blank","Name");
  16 lock (syncHandle)
  17 name = value;
  18 }
  19 }
  20 }
• 属性也可以是虚的,或者是抽象的.Properties have all the language features of methods. Properties can be virtual:
  1 public class Customer
  2 {
  3 public virtual string Name { get; set; }
  4 }

  这是C#3.0隐式声明语法.

• 你可以对get和set两个属性访问器做任何的修改,这比单单定义数据可见性强大的多.You can specify different accessibility modifiers to the get and set accessors in a property in C#. This gives you even greater control over the visibility of those data elements you expose as properties,这里也可以提供get-only或者set-only版本，甚至可以给读、写以不同的访问权限
  1 public class Customer
  2 {
  3 public virtual string Name
  4 {
  5 get;
  6 protected set;
  7 }
  8 }

Item 2: 使用只读方式,避免使用常量声明 Prefer readonly to const

• C#有两种常量版本,一种是编译时常量,另一种是运行时常量.错误的运用会导致性能和正确性降低.C# has two different versions of constants: compile-time constants and runtime constants. They have very different behaviors, and using the wrong one will cost you performance or correctness. 编译时常量比运行时常量稍微快点,但是灵活性差很多Compile-time constants are slightly faster, but far less flexible, than runtime constants

• 用readonly声明运行时常量,const声明编译时常量You declare runtime constants with the readonly keyword. Compile-time constants are declared with the const keyword.

• 编译时常量(const)可以在方法声明,运行时常量(readonly)不能在方法范围内声明Compile-time constants can also be declared inside methods. Read-only constants cannot be declared with method scope.

• 编译时常量被限制为数字,字符串类型.而运行时常量则可以是任何类型Compile-time constants are limited to numbers and strings. Read-only values are also constants, in that they cannot be modified after the constructor has executed. But read-only values are different in that they are assigned at runtime. You have much more flexibility in working with runtime constants. For one thing, runtime constants can be any type.

• 编译时常量与运行时常量行为的不同处在于它们的访问方式。编译时常量在编译后的结果代码中会被替换为该常量的值，例如下面的代码The differences in the behavior of compile-time and runtime constants follow from how they are accessed. A compile-time constant is replaced with the value of that constant in your object code. This construct:
  if (myDateTime.Year == Millennium)

  compiles to the same IL as if you had written this:

  if (myDateTime.Year == 2000)