C#用反射判断一个类型是否是Nullable同时获取它的根类型

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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)
Edward	1/1/1900	15/10/1990
Margaret	9/2/1950	[NULL]
Grant	13/6/1975	[NULL]

实际开发中应用

    /// <summary> 
        /// 集合装换DataSet 
        /// </summary> 
        /// <param name="list">集合</param> 
        /// <returns></returns> 
        /// 2008-08-01 22:08 HPDV2806 
        public static DataSet ToDataSet<T>(IList<T> p_List)
        {
            DataSet result = new DataSet();
            DataTable _DataTable = new DataTable();
            if (p_List.Count > 0)
            {
                PropertyInfo[] propertys = p_List[0].GetType().GetProperties();
                foreach (PropertyInfo pi in propertys)
                {


                    if (pi.PropertyType.IsGenericType && pi.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))
                    {    
                        _DataTable.Columns.Add(pi.Name, pi.PropertyType.GetGenericArguments()[0]);
                    }
                    else
                    {
                        _DataTable.Columns.Add(pi.Name, pi.PropertyType);
                    } 
                }

                for (int i = 0; i < p_List.Count; i++)
                {
                    ArrayList tempList = new ArrayList();
                    foreach (PropertyInfo pi in propertys)
                    {
                        object obj = pi.GetValue(p_List[i], null);
                        tempList.Add(obj);
                    }
                    object[] array = tempList.ToArray();
                    _DataTable.LoadDataRow(array, true);
                }
            }
            result.Tables.Add(_DataTable);
            return result;
        }