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詳解C#中使用對象或集合的初始值設(shè)定項(xiàng)初始化的操作

更新時間：2016年01月31日 14:49:38 投稿：goldensun

這篇文章主要介紹了詳解C#中使用對象或集合的初始值設(shè)定項(xiàng)初始化的操作,文中分別講了對對象和字典的初始化,需要的朋友可以參考下

使用對象初始值設(shè)定項(xiàng)初始化對象

可以使用對象初始值設(shè)定項(xiàng)以聲明方式初始化類型對象，而無需顯式調(diào)用類型的構(gòu)造函數(shù)。
下面的示例演示如何將對象初始值設(shè)定項(xiàng)用于命名對象。編譯器通過先訪問默認(rèn)實(shí)例構(gòu)造函數(shù)然后處理成員初始化處理對象初始值設(shè)定項(xiàng)。因此，如果默認(rèn)構(gòu)造函數(shù)在類中聲明為 private，那么需要公共訪問權(quán)的對象初始值設(shè)定項(xiàng)將失敗。

下面的示例演示如何使用對象初始值設(shè)定項(xiàng)初始化新的 StudentName 類型。

public class Program
{
  public static void Main()
  {

    // Declare a StudentName by using the constructor that has two parameters.
    StudentName student1 = new StudentName("Craig", "Playstead");

    // Make the same declaration by using an object initializer and sending 
    // arguments for the first and last names. The default constructor is 
    // invoked in processing this declaration, not the constructor that has
    // two parameters.
    StudentName student2 = new StudentName
    {
      FirstName = "Craig",
      LastName = "Playstead",
    };

    // Declare a StudentName by using an object initializer and sending 
    // an argument for only the ID property. No corresponding constructor is
    // necessary. Only the default constructor is used to process object 
    // initializers.
    StudentName student3 = new StudentName
    {
      ID = 183
    };

    // Declare a StudentName by using an object initializer and sending
    // arguments for all three properties. No corresponding constructor is 
    // defined in the class.
    StudentName student4 = new StudentName
    {
      FirstName = "Craig",
      LastName = "Playstead",
      ID = 116
    };

    System.Console.WriteLine(student1.ToString());
    System.Console.WriteLine(student2.ToString());
    System.Console.WriteLine(student3.ToString());
    System.Console.WriteLine(student4.ToString());
  }
}

這段的輸出是：

Craig 0
Craig 0
183
Craig 116

public class StudentName
{
  // The default constructor has no parameters. The default constructor 
  // is invoked in the processing of object initializers. 
  // You can test this by changing the access modifier from public to 
  // private. The declarations in Main that use object initializers will 
  // fail.
  public StudentName() { }

  // The following constructor has parameters for two of the three 
  // properties. 
  public StudentName(string first, string last)
  {
    FirstName = first;
    LastName = last;
  }

  // Properties.
  public string FirstName { get; set; }
  public string LastName { get; set; }
  public int ID { get; set; }

  public override string ToString()
  {
    return FirstName + " " + ID;
  }
}

下面的示例演示如何使用集合初始值設(shè)定項(xiàng)初始化一個 StudentName 類型集合。請注意，集合初始值設(shè)定項(xiàng)是一系列由逗號分隔的對象初始值設(shè)定項(xiàng)。

List<StudentName> students = new List<StudentName>()
{
 new StudentName {FirstName="Craig", LastName="Playstead", ID=116},
 new StudentName {FirstName="Shu", LastName="Ito", ID=112},
 new StudentName {FirstName="Gretchen", LastName="Rivas", ID=113},
 new StudentName {FirstName="Rajesh", LastName="Rotti", ID=114}
};

使用集合初始值設(shè)定項(xiàng)初始化字典

Dictionary<TKey, TValue> 包含鍵/值對集合。它的 Add 方法采用兩個參數(shù)，一個用于鍵，另一個用于值。若要初始化 Dictionary<TKey, TValue> 或其 Add 方法采用多個參數(shù)的任何集合，請將每組參數(shù)括在大括號中，如下面的示例所示。
示例
在下面的代碼示例中，使用 StudentName 類型的實(shí)例初始化一個 Dictionary<TKey, TValue>。

class StudentName
{
  public string FirstName { get; set; }
  public string LastName { get; set; }
  public int ID { get; set; }
}

class CollInit
{
  Dictionary<int, StudentName> students = new Dictionary<int, StudentName>()
  {
    { 111, new StudentName {FirstName="Sachin", LastName="Karnik", ID=211}},
    { 112, new StudentName {FirstName="Dina", LastName="Salimzianova", ID=317}},
    { 113, new StudentName {FirstName="Andy", LastName="Ruth", ID=198}}
  };
}

請注意集合的每個元素中的兩對大括號。最內(nèi)層的大括號括起了 StudentName 的對象初始值，而最外層的大括號括起了將要添加到 studentsDictionary<TKey, TValue> 中的鍵/值對的初始值。最后，字典的整個集合初始值括在一對大括號內(nèi)。

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