Listen to Podcast 106: Shipping | iDeveloper.
A few notes:
- RemObjects C# on iOS is based on LLVM, so I assume the other platforms use that too.
- Both guys are really busy shipping stuff, and it is hard.
–jeroen
Archive for the ‘C# 3.0’ Category
Podcast 106: Shipping | iDeveloper; about RemObjects C# and a lot of other stuff
Posted by jpluimers on 2014/03/13
Posted in .NET, C#, C# 1.0, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, RemObjects C#, Software Development | 2 Comments »
UINavigationController video when using Oxygene or Hydrogene Remobjects C# (via: remobjects)
Posted by jpluimers on 2014/03/07
Nice video when using either of the RemObjects Elements (Oxygene or Hydrogene): for creating a UI UINavigationController – remobjects.
–jeroen
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.NET/C#: DBNull explained
Posted by jpluimers on 2014/02/11
The DBNull type is a very special type in .NET. It represents null values in databases, which are slightly different than null values in .NET.
The biggest confusion that people have with it is that it won’t convert to anything. Which means that you see a lot of questions like “System.InvalidCastException: Conversion from type ‘DBNull’ to type” “is not valid”.
You’d think the full name would be System.Data.DBNull, it is actually named System.DBNull. The reason is that various other functionality of the System namespace depend on it, for instance the System.Convert class.
DBNull was already present in .NET 1.x, so it predates nullable types that were introduced in C# 2 / .NET 2.
A null value on the database side will result in a DBNull instance.
If you want to explicitly pass a null value to a database, you use a DBNull.Value, which is a singleton.
Why DBNull
There is a very interestin question/answer series on StackOverflow about this: via .net – What is the point of DBNull? – Stack Overflow.
There are a few good arguments both for and against DBNull.
But the baseline is that DBNull predates the introduction in the .NET framework of genuine nullable types. Both their behaviour is slightly different, so DBNull had to stay.
Which means you have to deal with it every now and then.
Invalid casts
A bit more background on the invalid casts.
It is thrown like this:
throw new InvalidCastException(Environment.GetResourceString("InvalidCast_DBNull"));
from
Convert.DefaultToType();
which is called from the DBNull method
object IConvertible.ToType(Type type, IFormatProvider provider);
All other IConvertible methods are implementated like
bool IConvertible.ToBoolean(IFormatProvider provider) { throw new InvalidCastException(Environment.GetResourceString("InvalidCast_FromDBNull")); }
So these all throw the same exception:
bool IConvertible.ToBoolean(IFormatProvider provider); byte IConvertible.ToByte(IFormatProvider provider); char IConvertible.ToChar(IFormatProvider provider); DateTime IConvertible.ToDateTime(IFormatProvider provider); decimal IConvertible.ToDecimal(IFormatProvider provider); double IConvertible.ToDouble(IFormatProvider provider); short IConvertible.ToInt16(IFormatProvider provider); int IConvertible.ToInt32(IFormatProvider provider); long IConvertible.ToInt64(IFormatProvider provider); sbyte IConvertible.ToSByte(IFormatProvider provider); float IConvertible.ToSingle(IFormatProvider provider); ushort IConvertible.ToUInt16(IFormatProvider provider); uint IConvertible.ToUInt32(IFormatProvider provider); ulong IConvertible.ToUInt64(IFormatProvider provider);
–jeroen
via:
- .net – What is the point of DBNull? – Stack Overflow.
- Handling Null Values.
- SqlDataReader.IsDBNull Method (System.Data.SqlClient).
- Convert.IsDBNull Method (System).
- .net – Checking for DBNull throws a StrongTypingException – Stack Overflow.
- System.Data.SqlTypes Namespace ().
- INullable Interface (System.Data.SqlTypes).
- DBNull Class (System).
- DBNull.Value Field (System).
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.NET/C#: When XmlSerializer throws “Unable to generate a temporary class (result=1).” / “error CS2001”
Posted by jpluimers on 2014/02/06
A while ago, I had this error when running an application on a hardened server:
Unhandled Exception:System.InvalidOperationException: Unable to generate a temporary class (result=1). error CS2001: Source file 'C:\windows\TEMP\0hocq2nq.0.cs' could not be found error CS2008: No inputs specified at System.Xml.Serialization.Compiler.Compile(Assembly parent, String ns, XmlSerializerCompilerParameters xmlParameters, Evidence evidence) at System.Xml.Serialization.TempAssembly.GenerateAssembly(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, Evidence evidence, XmlSerializerCompilerParameters parameters, Assembly assembly, Hashtable assemblies) at System.Xml.Serialization.TempAssembly..ctor(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, String location, Evidence evidence) at System.Xml.Serialization.XmlSerializer..ctor(Type type, XmlAttributeOverrides overrides, Type[] extraTypes, XmlRootAttribute root, String defaultNamespace, String location, Evidence evidence) at System.Xml.Serialization.XmlSerializer..ctor(Type type, XmlAttributeOverrides overrides, Type[] extraTypes, XmlRootAttribute root, String defaultNamespace, String location) at System.Xml.Serialization.XmlSerializer..ctor(Type type, Type[] extraTypes)
Usually I’m not the first with strange errors, but searching for “Unhandled Exception:System.InvalidOperationException: Unable to generate a temporary class” didn’t get many results.
This was a program running from SSIS under a non-system domain account with very little access.
My first guess was the right now: the XmlSerializer wants to generate a temporary C# file, then compile it into a temporary assembly. Since it cannot generate the C# file because the account does not have access to %windir\TEMP%, the compiler cannot find the (not generated) C# file.
After a few tries, I searched for XmlSerializer without GenerateAssembly, where the first hit ended at Changing where XmlSerializer Outputs Temporary Assemblies – Scott Hanselman.
That post indicated I should try looking for tempFilesLocation in the XmlSerializer context.
That got me these posts: Read the rest of this entry »
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.NET/C#/VB.NET – Default value for generics (via: Stack Overflow)
Posted by jpluimers on 2014/02/05
Looking for the pesky little differences between C# and VB.NET, I stumbled over this nice question by Micah Martin on default values for generics in VB.NET as compared to C#. Actually there were 3 questions, so I did a bit of post-editing:
How do I create the default for a generic in VB.NET? in C# I can call:
T variable = default(T);
- How do I do this in VB?
- If this just returns null (C#) or nothing (VB.NET) then what happens to value types?
- Is there a way to specify for a custom type what the default value is? For instance what if I want the default value to be the equivalent to calling a parameterless constructor on my class.
User Konrad Rudolph – Stack Overflow. promptly gave three answers:
Question 1:
Dim variable As T‘ or ‘Dim variable As T = Nothing‘ or ‘Dim variable As New T()Notice that the latter only works if you specifiy either theNewor theStructureconstraint for the generic type.Question 2:
For value types all members of the struct are “nulled” out, i.e. all reference type members are set to
null(Nothing) and all value types are in turn nulled out. And no, sincestringis a reference type, it does not result in""for strings as suggested in the other answer.Question 3:
No, there’s no way to specify this. There are some threads about this on Stack Overflow already, e.g. here. Jon has posted an excellent explanation why this is.
–jeroen
via: c# – Default value for generics – Stack Overflow.
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.NET/C#: refactoring some C# 1 code that uses HashTables as a poor mans property bag (via:Stack Overflow)
Posted by jpluimers on 2014/01/30
A while ago, I was refactoring some C# 1 code that uses HashTables as a poor mans property bag.
The problem was that I felt my code was convoluted, and should be denser, especially avoiding Convert.ChangeType. My code was already much simpler than casting tuples to a superclass.
So I asked this question on StackOverflow: c# – Is there a solution that feels less clumsy than Convert.ChangeType to get the value from a HashTable – Stack Overflow.
User dasblinkenlight showed it could be shortened and explained why (hyperlinks are mine):
Since System.String is sealed, the expression
genericType.IsSubclassOf(stringType)is the same as
genericType == stringTypeTherefore you do not need a call of Convert.ChangeType: you can cast to T by casting to object, like this:
object stringResult; // Note the change of type to "object" if (haveValue) stringResult = ((string)properties[propertyName]).Trim(); else stringResult = string.Empty; result = (T)stringResult; // It is allowed to cast object to generic T
The original .NET 1.1 code had loads of null checks wrapped if/then/else statements to assign default values for null values.
I wanted to get rid of that, and get code like this: Read the rest of this entry »
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.NET/C#: fun with enums and aliases part 2
Posted by jpluimers on 2014/01/29
In the .NET/C#: fun with enums and aliases part 1 you saw that an enumerated type can specify an underlying type.
The underlying type is limited to a strict set of built-in C# types: , so you cannot use a CTS type for it.
So you might think that you can only define enumeration values by integer constant like this:
namespace BeSharp
{
enum TwoState
{
False = 0,
True = 1,
}
enum ThreeState
{
False = 0,
True = 1,
Unknown = -1,
}
}
Well, you can do it like this too, since Operations between different enum types are allowed in another enum declaration: Read the rest of this entry »
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Faking num lock, caps lock and scroll lock leds – About My Code
Posted by jpluimers on 2014/01/21
I remember doing this in DOS ages ago (in the Turbo Pascal 5 era) for exactly the same reason: flash the keyboard LEDs to indicate some event was happening, but I’ve yet to find back the source code.
Here is how to do it in Windows using either C# or C: Faking num lock, caps lock and scroll lock leds – About My Code.
–jeroen
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.NET/C#: you cannot do string? because Nullable is for value type, and string is a reference type
Posted by jpluimers on 2014/01/15
At clients, I see quite a few people being confused by this compiler error message:
Error 1 The type 'string' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable'
One of the reasons about the confusion is that a string variable behaves like a value type, but in fact is a reference type because their values can consume a huge amount of memory (thanks User codekaizen).
A few interesting questions on that on StackOverflow:
- c# – Why strings behave like ValueType – Stack Overflow.
- c# – Why String behaves like value type while using == – Stack Overflow.
- In C#, why is String a reference type that behaves like a value type? – Stack Overflow.
- why string behaves as value type even though it is a reference type in c# – Stack Overflow.
- c# – Why .NET String is immutable? – Stack Overflow.
- .net – Is string a value type or a reference type? – Stack Overflow.
Anyway, back to the error message above.
Lots of people are confused by it, just see a few questions on StackOverflow: Read the rest of this entry »
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Posted in .NET, .NET 2.0, .NET 3.0, .NET 3.5, .NET 4.0, .NET 4.5, C#, C# 2.0, C# 3.0, C# 4.0, C# 5.0, Development, Jon Skeet, Software Development | Leave a Comment »
When two types are not the same: Assembly Load Contexts Subtleties (via: All Your Base Are Belong To Us)
Posted by jpluimers on 2014/01/09
Reading c# – Type.IsSubclassOf does not behave as expected – Stack Overflow, I found this very interesting link via Assembly Load Contexts Subtleties at Sasha Goldshtein’s blog (I love the name of the blog: All Your Base Are Belong To Us).
He explains the reasons for the error message
System.InvalidCastException: Unable to cast object of type ‘Plugin.MyPlugin’ to type ‘Plugin.MyPlugin’.
Actually his blog entry is an abstract of a 200+ page thesis on that is also recommended reading: Flexible Dynamic Linkin for .NET (by Anders Aaltonen, Alex Buckley and Susan Eisenbach).
–jeroen
via:
- Assembly Load Contexts Subtleties – All Your Base Are Belong To Us.
- Flexible Dynamic Linkin for .NET (by Anders Aaltonen, Alex Buckley and Susan Eisenbach)
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The Wiert Corner - irregular stream of stuff 