如何解决此问题，以将其通用转换为Nullable< T> ;？
问题描述：
我目前使用这种方便的转换扩展方法在类型之间进行转换：
I currently use this handy conversion extension method to do conversions between types:
public static T To<T>(this IConvertible obj)
{
return (T)Convert.ChangeType(obj, typeof(T));
}
但是，它不喜欢将有效值转换为Nullable，例如，这会失败：
However, it doesn't like converting valid values to Nullable, for example, this fails:
"1".To<int?>();
显然，很容易将1转换为（int？），但是会出现错误：
Obviously, 1 is easily converted to an (int?), but it gets the error:
Invalid cast from 'System.String' to 'System.Nullable`1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'.
这是一个明显简化的示例，实际上我正在使用它来进行类似字符串类型的转换因此：
This is an obviously simplified example, in reality I'm using it to do conversions from string types like so:
packageDb.Quantity = package.package.ElementDeep(Namespace + "PackageQuantity", Namespace + "ActualQuantity", Namespace + "Quantity").ValueOrNull().To<int?>();
如果Convert.ChangeType不喜欢Nullable，那么有人有什么好主意吗？
If Convert.ChangeType doesn't like Nullable, anyone have any great ideas?
答
public static T To<T>(this IConvertible obj)
{
Type t = typeof(T);
Type u = Nullable.GetUnderlyingType(t);
if (u != null)
{
return (obj == null) ? default(T) : (T)Convert.ChangeType(obj, u);
}
else
{
return (T)Convert.ChangeType(obj, t);
}
}