我知道这个问题很老，但我对我所做的扩展方法也有同样的问题。使用 Marc Gravell 的响应，我能够修改我的代码。此扩展方法将处理原始类型、字符串、枚举和具有原始属性的对象的列表。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Text;
/// <summary>
/// Converts a List<T> to a DataTable.
/// </summary>
/// <typeparam name="T">The type of the list collection.</typeparam>
/// <param name="list">List instance reference.</param>
/// <returns>A DataTable of the converted list collection.</returns>
public static DataTable ToDataTable<T>(this List<T> list)
{
var entityType = typeof (T);
// Lists of type System.String and System.Enum (which includes enumerations and structs) must be handled differently
// than primitives and custom objects (e.g. an object that is not type System.Object).
if (entityType == typeof (String))
{
var dataTable = new DataTable(entityType.Name);
dataTable.Columns.Add(entityType.Name);
// Iterate through each item in the list. There is only one cell, so use index 0 to set the value.
foreach (T item in list)
{
var row = dataTable.NewRow();
row[0] = item;
dataTable.Rows.Add(row);
}
return dataTable;
}
else if (entityType.BaseType == typeof (Enum))
{
var dataTable = new DataTable(entityType.Name);
dataTable.Columns.Add(entityType.Name);
// Iterate through each item in the list. There is only one cell, so use index 0 to set the value.
foreach (string namedConstant in Enum.GetNames(entityType))
{
var row = dataTable.NewRow();
row[0] = namedConstant;
dataTable.Rows.Add(row);
}
return dataTable;
}
// Check if the type of the list is a primitive type or not. Note that if the type of the list is a custom
// object (e.g. an object that is not type System.Object), the underlying type will be null.
var underlyingType = Nullable.GetUnderlyingType(entityType);
var primitiveTypes = new List<Type>
{
typeof (Byte),
typeof (Char),
typeof (Decimal),
typeof (Double),
typeof (Int16),
typeof (Int32),
typeof (Int64),
typeof (SByte),
typeof (Single),
typeof (UInt16),
typeof (UInt32),
typeof (UInt64),
};
var typeIsPrimitive = primitiveTypes.Contains(underlyingType);
// If the type of the list is a primitive, perform a simple conversion.
// Otherwise, map the object's properties to columns and fill the cells with the properties' values.
if (typeIsPrimitive)
{
var dataTable = new DataTable(underlyingType.Name);
dataTable.Columns.Add(underlyingType.Name);
// Iterate through each item in the list. There is only one cell, so use index 0 to set the value.
foreach (T item in list)
{
var row = dataTable.NewRow();
row[0] = item;
dataTable.Rows.Add(row);
}
return dataTable;
}
else
{
// TODO:
// 1. Convert lists of type System.Object to a data table.
// 2. Handle objects with nested objects (make the column name the name of the object and print "system.object" as the value).
var dataTable = new DataTable(entityType.Name);
var propertyDescriptorCollection = TypeDescriptor.GetProperties(entityType);
// Iterate through each property in the object and add that property name as a new column in the data table.
foreach (PropertyDescriptor propertyDescriptor in propertyDescriptorCollection)
{
// Data tables cannot have nullable columns. The cells can have null values, but the actual columns themselves cannot be nullable.
// Therefore, if the current property type is nullable, use the underlying type (e.g. if the type is a nullable int, use int).
var propertyType = Nullable.GetUnderlyingType(propertyDescriptor.PropertyType) ?? propertyDescriptor.PropertyType;
dataTable.Columns.Add(propertyDescriptor.Name, propertyType);
}
// Iterate through each object in the list adn add a new row in the data table.
// Then iterate through each property in the object and add the property's value to the current cell.
// Once all properties in the current object have been used, add the row to the data table.
foreach (T item in list)
{
var row = dataTable.NewRow();
foreach (PropertyDescriptor propertyDescriptor in propertyDescriptorCollection)
{
var value = propertyDescriptor.GetValue(item);
row[propertyDescriptor.Name] = value ?? DBNull.Value;
}
dataTable.Rows.Add(row);
}
return dataTable;
}
}