C#用反射判斷一個類型是否是Nullable同時獲取它的根類型

在我們的應用程序中我們使用類描述我們的業務對象，為我們產生一些報表之類的，那就依賴大量不同的對象，我們創建一個幫助方法來轉換我們的業務對象，或是一個List的業務對象到DataTables.

由於數據庫表中字段可為null,對應.net 2.0以后我們可用Nullable類型來實現，那當我們業務對象類中字段有null時，並需要轉換為DataTable時，這個場景產生，你可能用到以下方法：

下面的代碼是一個list對象(不支持處理復雜類型)返回一個描述對象的DataTable

/// <summary>
 /// Converts a Generic List into a DataTable
 /// </summary>
 /// <param name="list"></param>
 /// <param name="typ"></param>
 /// <returns></returns>
 private DataTable GetDataTable(IList list, Type typ)
 {
     DataTable dt = new DataTable();

     // Get a list of all the properties on the object
     PropertyInfo[] pi = typ.GetProperties();

     // Loop through each property, and add it as a column to the datatable
     foreach (PropertyInfo p in pi)
     {
         // The the type of the property
         Type columnType = p.PropertyType;

         // We need to check whether the property is NULLABLE
         if (p.PropertyType.IsGenericType && p.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))
         {
             // If it is NULLABLE, then get the underlying type. eg if "Nullable<int>" then this will return just "int"
             columnType = p.PropertyType.GetGenericArguments()[0];
         }

         // Add the column definition to the datatable.
         dt.Columns.Add(new DataColumn(p.Name, columnType));
     }

     // For each object in the list, loop through and add the data to the datatable.
     foreach (object obj in list)
     {
         object[] row = new object[pi.Length];
         int i = 0;

         foreach (PropertyInfo p in pi)
         {
             row[i++] = p.GetValue(obj, null);
         }

         dt.Rows.Add(row);
     }

     return dt;
 }

上面的代碼的關鍵點：

• 用 PropertyType.IsGenericType 決定property是否是generic類型
• 用 ProprtyType.GetGenericTypeDefinition() == typeof(Nullable<>) 檢測它是否是一個nullable類型
• 用 PropertyType.GetGenericArguments() 獲取基類型。

下面讓我們來應用一下：

public class Person
{
    public string Name { get; set; }
    public DateTime DateOfBirth { get; set; }
    public DateTime? DateOfDeath { get; set; }
}

public class Example
{
    public static DataTable RunExample()
    {
        Person edward = new Person() { Name = "Edward", DateOfBirth = new DateTime(1900, 1, 1), DateOfDeath = new DateTime(1990, 10, 15) };
        Person margaret = new Person() { Name = "Margaret", DateOfBirth = new DateTime(1950, 2, 9), DateOfDeath = null };
        Person grant = new Person() { Name = "Grant", DateOfBirth = new DateTime(1975, 6, 13), DateOfDeath = null };

        List<Person> people = new List<Person>();

        people.Add(edward);
        people.Add(margaret);
        people.Add(grant);

        DataTable dt = GetDataTable(people, typeof(Person));

        return dt;
    }
}

將返回的DataTable像下面的內容:

Name (string)	DateOfBirth (DateTime)	DateOfDeath (DateTime)
Edward	1/1/1900	15/10/1990
Margaret	9/2/1950	[NULL]
Grant	13/6/1975	[NULL]