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 | A note about as
Wjousts | 5:16 24 Jul '09 |
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Note: the as keyword will only work with reference types since value types can't be null.
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| Converting Variables
SashoJ | 8:32 29 Jun '09 |
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Please answer:
Is there a way to Convert variable with type as a String parameter?
Can you write a function like this:
a = MyTryCast(variable as Object, SystemType As String)
and then use it like:
a = MyTryCast("12.13", "System.Decimal")
without use of
Select Case SystemType
Case "System.String"
return CType(variable, String)
...
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| Missing a lot
JoshMouch | 15:27 25 Feb '07 |
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No offense, but this article is missing a lot. Each C# & VB.Net casting feature has an equivalent.
For example:
The VB.Net's equivalent to C#'s "as" is TryCast()
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| difference VB/C# in compile-time vs run-time error
Alexis Rzewski | 5:51 7 Feb '07 |
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one BIG difference between C# and VB:
C# compiler will never allow
int myInt = (int) "3";
VB.NET compiler, even with Option Strict ON will always allow
Dim myInt as Integer = CType ("3", Integer)
Both languages understand the .NET class System.Convert:
myInt = System.Convert.ToInt32("3")
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| How about casting arrays
eschneider100 | 9:57 19 Mar '05 |
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How about and example on casting arrays.
Thanks
Schneider
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I would like to figure out how to do this to.
This is something like what I would like to do...
Public Sub SortMyArray(aValues() as Object)
if typeof aValues is String() then
SortStrings(directcast(aValues,string())
elseif typeof aValues is SomeOtherObject() then
SortOtherObjects(directcast(aValues,SomeOtherObject())
end if
End Sub
Private Sub SortStrings(asValues() as String)
'Do the sort
End Sub
Private Sub SortOtherObjects(aValues() as SomeOtherObject)
'Do the sort
End Sub
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| ToString
George_Seremetidis | 14:40 28 Sep '04 |
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I prefer to use ToString rather than CType for certain things. ToString will return an empty string if a column is a NULL in a DataRow. CType will throw an exception on a NULL.
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| Don't Forget System.Convert.ChangeType
Shaun Hayward | 8:35 29 Jun '04 |
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Good article.
Another important conversion method is the System.Convert class's ChangeType method - especially when you're using Reflection.
The problem with GetType is that the second parameter must accept the name of the type but cannot accept an instance of System.Type (at least no way that I could find).
So you can't do the following:
obj2 = CType(SomeValue, obj1.GetType)
This was a REAL problem when trying to convert strings to an EXACT datatype to use the SetValue method in Reflection. The solution:
obj2 = System.Convert.ChangeType(SomeValue, obj1.GetType)
Something worth investigating and possibly adding to the article.
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Thank you for pointing out Convert.ChangeType function. This is more important for me then entire article.  
P.S. However, this function has one limitation- value has to implement IConvertible interface
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| Problems with casting objects
simbakid | 4:04 3 Mar '04 |
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I have a problem in my code with regard casting. I have a base class object called BaseDAO, a subclass is created from this called CustomerRowSet. I have a function which, through reflection, will create an instance of the subclass.
public static BaseDAO newInstance (DAOAssembly cAssembly, string strProviderID)
{
BaseDAO cDAO = m_cManager.lookup(cAssembly, strProviderID);
if (cDAO != null)
{
Console.WriteLine("Created DAO Instance");
}
else
{
Console.WriteLine("Failed to create specified DAO handler");
}
return cDAO;
}
I make a call to the newInstance function and test the type of the returned object, thus:
DAOAssembly x = new DAOAssembly("DAOTest.dll", "d:", "ds.xml", "d:", "TEST");
Object o = CustomerRowSet.newInstance(x, "SELECT_CUSTOMERS");
if (o is DAOTest.CustomerRowSet)
{
Console.WriteLine("Object is of correct type");
}
else
{
System.Type t;
t = o.GetType();
Console.WriteLine(t.FullName);
}
Upon return, execution branches into the else statement and not the if statement, but the output from code is:
Created DAO Instance
DAOTest.CustomerRowSet
This shows that the returned object is of the correct type yet doesn't execute the if branch of the code. In addition, if I try the following code:
CustomerRowSet rs = (CustomerRowSet)CustomerRowSet.newInstance(x, "SELECT_CUSTOMERS");
I get an InvalidCastException.
Grateful for any suggestions or information, many thanks in advance.
Chris.
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| Difference between DirectCast and Ctype?
FruitBatInShades | 6:36 26 Jan '04 |
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If the specified type and the run-time type of the expression are the same, however, the run-time performance of DirectCast is better than that of CType.
So which function gives the best performance under all circumstances? Can you give an example of what type of conversions cause DirectCast to throw!
Thanks
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| Please add pointers to the next update!
Anonymous | 14:20 4 Oct '03 |
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Please add pointers in the next update, they are still used in C# and casting can be done with them. I am particularly having trouble with pointers in my COM Interop which involves casting.
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| OK, but could be better
David Bennett | 5:23 30 Sep '03 |
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>>>C# is a strictly typed language. Whenever types don't match, casting is necessary.
This is simply not true. C# allows you to upcast and perform implicit conversions (eg double to int) without needing a cast.
The whole issue of implicit vs explicit is not mentioned.
The existence of a range of other conversion functions (CInt, CDbl, etc) is ignored. Likewise the Convert functions, ToString(), etc.
I'll wait for V2.
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| Informative
Nishant S | 21:14 23 Sep '03 |
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| Comments
Nick Seng | 16:21 23 Sep '03 |
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Where were you when I just started doing C# & VB.Net? 
Anyway, a couple of comments:
1) Your explaination of DirectCast isn't really clear. Maybe it would help if you showed some example.
2) I don't really see the difference for point 4 & 5.
Besides that good article. A lot of newbie would undoubtably find it helpfull 
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| Good
dog_spawn | 14:14 23 Sep '03 |
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I liked the style of this article as you consider both C# and VB.NET. I learnt something new - I did not know about the as operator
Do any C++ purists agree with me when I say: casting is never needed in good OO design.
Even in an XML parser you don't need it. Consider a simple example: if you can always predict what nodes you might need to 'cast' into you can provide a function:
CommentElement Node::GetAsComment()
...where Node is the superclass of all Xml element nodes.
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dog_spawn wrote:
Do any C++ purists agree with me when I say: casting is never needed in good OO design.
Just off the top of my head, here are some examples where very good design in C# requires casting:
* Creating a plug-in architecture - try loading and instantiating dynamically assemblies without polymorphic reflection tests and casting.
* Using pretty much any of the Asynchronous programming methods in the FCL - all use boxing and un-boxing, which can't be done without casting.
* Adding queue items that return values to a the ThreadPool requires boxing and un-boxing, which again is casting.
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You seem to have missed my point. I will try to explain myself better.
Obviously using C# requires casting. But that is because most of the framework is not designed as well as it could be. My point is about design not about the way the framework happens to be setup
Most of the time we only cast because C# doesn't allow us to make specialized collections easily enough yet. 'generics' will solve that hopefully.
No plugin architecture ever needs casting. Any plugin object inherits some interface. Obviously a give program only knows about the interface. If you end up casting using plugin objects your interfaces need redesigning
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| Re: Good
Rudi Breedenraedt | 6:22 25 Sep '03 |
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First, thanks for the compliment!
Concerning your good OO design (btw, I don't know if C++ purists are by definition to be considered as OO purists, but please, let's not start that discussion here... ):
Casting is in my opinion not a matter of design. Casting originates from the fact that the implementation is done in a strong-typed language. Would you implement in a purely object-oriented language as SmallTalk, then you would never have to cast, since it does no typechecking, and even does not know what casting is...
Now, should you design in such a way that casting will not be necessary in an implementation language ? My answer would again be no. Good OO designs are caracterised by their good distribution of responsibilities. Is it a good distribution of responsibility to have the superclass know about all it's (current but also future !?!) subclasses, since it should provide GetAsSubclass methods for each one of them ? I believe the contrary. By the way, as I pointed out, you can only provide GetAs methods for known (=current) subclasses, so you disallow extension by subclassing by 3rd parties. Wasn't OO meant to be extended that way ?
Consequently, if C# requires casting, it's not due to bad design (although design could have been better), but due to it's strong-typed character.
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Rudi Breedenraedt wrote:
Consequently, if C# requires casting, it's not due to bad design (although design could have been better), but due to it's strong-typed character.
C# is a strongly typed language. However the collections are not, hence my comments about bad design.
I think you have got mixed up here You do not need casting with a strongly typed language. That is the point of types. C# requires casting so frequently because of the bad design of the collections.
Rudi Breedenraedt wrote:
I believe the contrary
I agree it is bad design to have GetAsSubclass method However that is a better solution than casting. This problem can be solved by good design. For example GetElementsByTagName in the XML part of the framework should return a list of XmlElements, not a list of XmlNodes as it currently does.
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Casting in C# is nothing else than querying for another interface. The cast is verified to be valid. So what?
"Vierteile den, der sie Hure schimpft mit einem türkischen Säbel."
sighist | Agile Programming | doxygen
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Heh, well 'So what?' is a perfectly practical point of view It kind of misses the point but it's less hard work.
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What is the difference between a cast and a QueryInterface in C# ?
"Vierteile den, der sie Hure schimpft mit einem türkischen Säbel."
sighist | Agile Programming | doxygen
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