如何执行typeof [英] How to execute a typeof

问题描述

我有一个包含一些列的数据表.我想获取一列的类型并将其放在此命令中:

Hi,
I have a DataTable that contains some columns. I want to get the type of one column and put it in this command:

dataRow1.Field<"I wrote here dataRow1.Table.Columns["columnName"].DataType>("columnName")

但这没用.

在此先谢谢您.

But it''s not worked.

Thanks in advance.

推荐答案

您应该在通用参数中定义实际的数据类型.例如，如果列为string，则:

You should define the actual datatype in the generic parameter. For example if the column is string, then:

dataRow1.Field<string>("columnName")

等等.

不幸的是，泛型不能那样工作.

泛型类型参数必须在编译时已知，并且不能是运行时因变量

我建议要么使用通用基类(对象)，要么创建一种方法来测试运行时数据类型，并使用正确的设计时指定的通用类型参数:

Unfortunately generics don''t work like that.

Generic type parameters must be known at compile-time and cannot be a runtime dependent variable

I would suggest either working with a common base class (object) or creating a method that tests the runtime datatype and uses the correct, design-time specified, generic type argument:

if(dataRow1.Table.Columns["columnName"].DataType == typeof(string))
{
   //use dataRow1.Field<string>("columnName")
}
else if (dataRow1.Table.Columns["columnName"].DataType == typeof(int))
{
   //use dataRow1.Field<int>("columnName")
}
...

这篇关于如何执行typeof的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！