C#用反射判断一个类型是否是Nullable同时获取它的根类型

时间:2022-10-10 17:01:43

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]