Convert.ChangeType doesn't handle nullables

re: Convert.ChangeType doesn't handle nullables

Thomas Jensen — Wed, 18 Feb 2009 22:20:37 GMT

public static T ChangeType<T>(object value)

{

Type conversionType = typeof(T);

if (conversionType.IsGenericType && conversionType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))

{

if (value == null)

{

return default(T);

}

else

{ NullableConverter nullableConverter = new NullableConverter(conversionType);

conversionType = nullableConverter.UnderlyingType;

}

return (T)Convert.ChangeType(value, conversionType);

}

re: Convert.ChangeType doesn't handle nullables

Idrees — Mon, 21 Jul 2008 12:37:45 GMT

Great work. especially the generic method.

Thankx.

re: Convert.ChangeType doesn't handle nullables

vkelman — Tue, 08 Jul 2008 22:46:31 GMT

I slightly modified your http://aspalliance.com/852 code. I canno tput code there due to server error.

I modified your code slightly, to make it generic. Thanks!

public static T ChangeType<T>(object value) {

Type conversionType = typeof(T);

if (conversionType.IsGenericType &&

conversionType.GetGenericTypeDefinition().Equals(typeof(Nullable<>))) {

if (value == null) { return default(T); }

conversionType = Nullable.GetUnderlyingType(conversionType); ;

}

return (T)Convert.ChangeType(value, conversionType);

}

re: Convert.ChangeType doesn't handle nullables

Andrew — Mon, 28 Jan 2008 23:37:58 GMT

Very elegant solution Rich, love it. Thanks.

re: Convert.ChangeType doesn't handle nullables

Chris Carter — Tue, 27 Nov 2007 05:20:42 GMT

Thanks Rich, that rocks!

re: Convert.ChangeType doesn't handle nullables

Martin — Wed, 14 Nov 2007 16:02:52 GMT

Excellent solution Rich. Thanks.

re: Convert.ChangeType doesn't handle nullables

Rich — Wed, 31 Oct 2007 22:14:18 GMT

Thanks was looking into this issue..

How about this as an option?

public static class Converter {

public static T ChangeType<T>(object value) {

TypeConverter tc = TypeDescriptor.GetConverter(typeof(T));

return (T)tc.ConvertFrom(value);

}

public static void RegisterTypeConverter<T, TC>() where TC : TypeConverter {

TypeDescriptor.AddAttributes(typeof(T), new TypeConverterAttribute(typeof(TC)));

}

This allows you to create new TypeDescriptors and add them at runtime, for any missing converters e.g. Version

public class VersionConverter : TypeConverter

{

public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value) {

string strvalue = value as string;

if (strvalue != null) {

return new Version(strvalue);

}

else {

return new Version();

}

Test code...

static void Main(string[] args) {

Converter.RegisterTypeConverter<Version, VersionConverter>();

int? i = Converter.ChangeType<int?>("123");

DateTime dt = Converter.ChangeType<DateTime>("20:33");

char c = Converter.ChangeType<char>("x");

Guid g = Converter.ChangeType<Guid>("{32F92EEB-A703-4eb7-A9F8-62E09F87D03F}");

Version v = Converter.ChangeType<Version>("1.2.3.4");

DateTime? k = Converter.ChangeType<DateTime?>(null);

}

http://aspalliance.com/852

TrackBack — Wed, 31 May 2006 15:33:42 GMT

The PumaCode.org Blog: using Convert.ChangeType() on nullable types in C#

TrackBack — Fri, 19 May 2006 19:24:00 GMT

The PumaCode.org Blog: using Convert.ChangeType() on nullable types in C#

re: Convert.ChangeType doesn't handle nullables

Paul Wilson — Tue, 07 Feb 2006 19:39:00 GMT

By the way, the call to QueryHelper.ChangeType is just a recursive call on the exact same method, so change the QueryHelper class name to your own class name.