Nullable 类型的转换
今天碰到Nullable 不能通过Convert.ChangeType转换,辛苦在网上找到两个解决方法,共享一下。
1.The PumaCode.org Blog
2.Paul Wilson's .NET Blog
引用:http://weblogs.asp.net/pjohnson/archive/2006/02/07/437631.aspx
1.The PumaCode.org Blog
public object ChangeType(object value, Type conversionType)
{
if ( conversionType.IsGenericType &&
conversionType.GetGenericTypeDefinition( ).Equals( typeof( Nullable<> ) ) ) {
if(value == null)
return null;
System.ComponentModel.NullableConverter nullableConverter
= new System.ComponentModel.NullableConverter(conversionType);
conversionType = nullableConverter.UnderlyingType;
}
return Convert.ChangeType(value, conversionType);
}
引用:http://blog.pumacode.org/2006/05/18/using-convert-changetype-on-nullable-types/{
if ( conversionType.IsGenericType &&
conversionType.GetGenericTypeDefinition( ).Equals( typeof( Nullable<> ) ) ) {
if(value == null)
return null;
System.ComponentModel.NullableConverter nullableConverter
= new System.ComponentModel.NullableConverter(conversionType);
conversionType = nullableConverter.UnderlyingType;
}
return Convert.ChangeType(value, conversionType);
}
2.Paul Wilson's .NET Blog
public class DataTypeConverter
{
public static object ChangeType(Type type,object value)
{
if ((value == null) && type.IsGenericType)
{
return Activator.CreateInstance(type);
}
if (value == null)
{
return null;
}
if (type == value.GetType())
{
return value;
}
if (type.IsEnum)
{
if (value is string)
{
return Enum.Parse(type, value as string);
}
return Enum.ToObject(type, value);
}
if (!type.IsInterface && type.IsGenericType)
{
Type type1 = type.GetGenericArguments()[0];
object obj1 = DataTypeConverter.ChangeType(type1,value);
return Activator.CreateInstance(type, new object[] { obj1 });
}
if ((value is string) && (type == typeof(Guid)))
{
return new Guid(value as string);
}
if ((value is string) && (type == typeof(Version)))
{
return new Version(value as string);
}
if (!(value is IConvertible))
{
return value;
}
return Convert.ChangeType(value, type);
}
}
这个代码是WilsonORMapper中的QueryHelper类,不好意思,我Reflector了一下。{
public static object ChangeType(Type type,object value)
{
if ((value == null) && type.IsGenericType)
{
return Activator.CreateInstance(type);
}
if (value == null)
{
return null;
}
if (type == value.GetType())
{
return value;
}
if (type.IsEnum)
{
if (value is string)
{
return Enum.Parse(type, value as string);
}
return Enum.ToObject(type, value);
}
if (!type.IsInterface && type.IsGenericType)
{
Type type1 = type.GetGenericArguments()[0];
object obj1 = DataTypeConverter.ChangeType(type1,value);
return Activator.CreateInstance(type, new object[] { obj1 });
}
if ((value is string) && (type == typeof(Guid)))
{
return new Guid(value as string);
}
if ((value is string) && (type == typeof(Version)))
{
return new Version(value as string);
}
if (!(value is IConvertible))
{
return value;
}
return Convert.ChangeType(value, type);
}
}
引用:http://weblogs.asp.net/pjohnson/archive/2006/02/07/437631.aspx