Understanding Static Constructor, 理解静态构造函数

引言:

想起这个问题是一次面试提到的题目而起，而之前也有关于静态构造函数和构造函数区别, 于是有了这次探索.

用法:

1. 初始化静态成员数据

   1: public class MyTest

   2: {

   3:     static string Str = "This is MyTest";    

   4:     static int i = 0;

   5:  

   6:     static MyTest()

   7:     {

   8:         Str = "Hi, I am Initialized";

   9:         i++;            

  10:     }

  11: }

2. 初始化静态readonly成员

   1: public class MyTest

   2: {

   3:     static readonly string MyReadonlyData = "MyTest's MyReadonlyData";

   4:     

   5:     static MyTest()

   6:     {

   7:         MyReadonlyData = ":), Has been modifyed in static contructor";    

   8:     }

   9: }

实现层次:

对应的il代码结构, 所谓cctor, 是类中定义初始化数据的方法

在.Net对于赋值操作又分为两种方式

1. precise
2. beforefieldinit

precise 执行方式

   1: public class AnotherTest

   2: {

   3:         static AnotherTest() {

   4:  

   5:         }

   6:         public static string Test = "This is a test from another test";

   7: }

beforefieldinit

   1: public class AnotherTest

   2: {

   3:     public static string Test = "This is a test from another test";

   4: }

所谓beforefieldinit是指在数据被调用前初始化数据.

至于il代码，也是在class定义时添加了一个beforefieldinit标记, 在初始化数据时于是我们建议使用constructor chain来初始化数据，所谓constrcutor chain:

   1: namespace XWang

   2: {

   3:     public class Test

   4:     {

   5:         int A;

   6:         int B;

   7:         int C;

   8:         string InitialConfigurations;

   9:     

  10:         // The Constructor to initialize the private datas

  11:         public Test()

  12:         {

  13:             B = 2;

  14:             C = 3;

  15:         }

  16:  

  17:         // Initalize the a and call the default parameterless constructor

  18:         public Test(int a) : this()

  19:         {

  20:             A = a;

  21:         }

  22:  

  23:         // A Constructor Chain to initialize the datas

  24:         public Test(string configuration, int a): this(a)

  25:         {

  26:             InitialConfigurations = configuration;

  27:         }        

  28:     }

  29: }

对于静态构造函数，我们也应该在静态构造函数中初始化数据

   1: namespace XWang

   2: {

   3:     public class StaticConstructorTest

   4:     {

   5:         static string StaticData;

   6:  

   7:         static StaticConstructorTest()

   8:         {

   9:             StaticData = "Hi, I am initialized";

  10:         }

  11:     }

  12: }

同时这也是Effective C#中提到的其中几个原则:

• 条款12：变量初始化器优于赋值语句
• 条款13：使用静态构造器初始化静态类成员
• 条款14：利用构造器链

Have Fun :)