C#用反射判断一个类型是否是Nullable同时获取它的根类型



在我们的应用程序中我们使用类描述我们的业务对象，为我们产生一些报表之类的，那就依赖大量不同的对象，我们创建一个帮助方法来转换我们的业务对象，或是一个List的业务对象到DataTables.

由于数据库表中字段可为null,对应.net 2.0以后我们可用Nullable类型来实现，那当我们业务对象类中字段有null时，并需要转换为DataTable时，这个场景产生，你可能用到以下方法：

下面的代码是一个list对象(不支持处理复杂类型)返回一个描述对象的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; }

上面的代码的关键点：

• 用 PropertyType.IsGenericType 决定property是否是generic类型
• 用 ProprtyType.GetGenericTypeDefinition() == typeof(Nullable<>) 检测它是否是一个nullable类型
• 用 PropertyType.GetGenericArguments() 获取基类型。

下面让我们来应用一下：

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;    }}

将返回的DataTable像下面的内容:

Name (string)DateOfBirth (DateTime)DateOfDeath (DateTime)Edward1/1/190015/10/1990Margaret9/2/1950[NULL]Grant13/6/1975[NULL]