这是今天真的绊倒了我。我敢肯定，它并不难，但我有一个System.Reflection.PropertyInfo对象。我想设置基于数据库查询的结果它的价值（考虑ORM，映射列回属性）。

This is really stumping me today. I'm sure its not that hard, but I have a System.Reflection.PropertyInfo object. I want to set its value based on the result of a database lookup (think ORM, mapping a column back to a property).

我的问题是，如果数据库返回的值是为DBNull，我只是想将属性值设置为默认值，与调用：

My problem is if the DB returned value is DBNull, I just want to set the property value to its default, the same as calling:

value = default(T);  // where T is the type of the property.

不过，如果你给它一个类型，默认（）方法将不会编译这是我有：

However, the default() method won't compile if you give it a Type, which is what I have:

object myObj = ???; // doesn't really matter. some arbitrary class.
PropertyInfo myPropInf = ???; // the reflection data for a property on the myObj object.
myPropInf.SetValue(myObj, default(myPropInf.PropertyType), null);

以上不能编译。默认（Type）为无效。我也想过这样做的：

The above doesn't compile. default(Type) is invalid. I also thought about doing:

object myObj = ???;
PropertyInfo myPropInf = ???;
myPropInf.SetValue(myObj, Activator.CreateInstance(myPropInf.PropertyType), null);

然而，如果类型为字符串，将分配值新的String（），但我真的想空，这是默认值（字符串）将返回。

However, if the Type is string, that would assign the value "new String()", but I really want "null", which is what "default(string)" would return.

那么，我在这里丢失？ 我想一个真正哈克的方法是创建一个MyObj中的类型的新实例，复制属性过，但似乎只是愚蠢的......

So what am I missing here? I suppose a really hacky way would be to create a new instance of myObj's Type and copy the property over, but that just seems stupid...

object myObj = ???;
PropertyInfo  myPropInf = ???;
var blank = Activator.CreateInstance(myObj.GetType());
object defaultValue = myPropInf.GetValue(blank, null);
myPropInf.SetValue(myObj, defaultValue, null);

我宁愿不浪费内存，打造了一个全新的实例，只是为了得到默认的属性，虽然。似乎很浪费的。

I'd rather not waste the memory to make a whole new instance, just to get the default for the property though. Seems very wasteful.

任何想法？

推荐答案

我相信，如果你只是做

prop.SetValue(obj,null,null);

如果它是一个值类型，它会设置为默认值，如果它是一个引用类型，它会设置为null。

If it's a valuetype, it'll set it to the default value, if it's a reference type, it'll set it to null.