Dynamic Typecasting

[Guest]

I have a variable and a data-type string stored in a database. I need to
dynamically cast the variable to the datatype at run-time. I am able to
create the Type from the data-type string, but I am not able to cast it
correctly. Here is an example of my code, although realize that I would need
to accomplish this with any type (Boolean, Guid, String, Integer...), and not
just GUID:

Dim typeStr as String = "System.GUID"
Dim myType As Type = Type.GetType(typeStr, True, True)
Dim varStr as String = "81db359d-a970-4247-89f8-67995412da35"

'this is the code that does not work. myType gets underlined in blue,
saying "Type 'tmpType' is not defined."
varStr = CType(varStr, myType)

 

[Cor Ligthert[MVP]]

Hi Honus,

Why you want to do it this, way, it sounds to me as.

I need a billion dollars tomorrow, can you tell me how to do that?

Cor

 

[Armin Zingler]

I have a variable and a data-type string stored in a database. I
need to dynamically cast the variable to the datatype at run-time.
I am able to create the Type from the data-type string, but I am not
able to cast it correctly. Here is an example of my code, although
realize that I would need to accomplish this with any type (Boolean,
Guid, String, Integer...), and not just GUID:

Dim typeStr as String = "System.GUID"
Dim myType As Type = Type.GetType(typeStr, True, True)
Dim varStr as String = "81db359d-a970-4247-89f8-67995412da35"

'this is the code that does not work. myType gets underlined in
blue, saying "Type 'tmpType' is not defined."
varStr = CType(varStr, myType)

What you want to do is contradictive:
- Casting is done by the compiler. The compiler must know the destination
type.
- Your destination type is unknown at compile time, therefore it can not
work.


Armin

 

[Herfried K. Wagner [MVP]]

I have a variable and a data-type string stored in a database. I need to
dynamically cast the variable to the datatype at run-time.

Casting is primarily a compile-time feature which will help the compiler to
detect certain flaws in the code.

If you are talking about type conversions, take a look at the
'TypeConverter' class.

 

[Guest]

Your synnicism is refreshing and envigorating. Oh wait, never mind.

 

[Cor Ligthert[MVP]]

Honus,

Your synnicism is refreshing and envigorating. Oh wait, never mind.

What you call this what you are now writing, informing us in a way that we
able to help you?

We are sharing information here, that is not in one direction, we try to
learn from each other.

Cor

 

[Guest]

How is an object of type List (of String) serialized into the database?

 

[Phill W.]

I have a variable and a data-type string stored in a database. I need to
dynamically cast the variable to the datatype at run-time. I am able to
create the Type from the data-type string, but I am not able to cast it
correctly.

Dim typeStr as String = "System.GUID"
Dim myType As Type = Type.GetType(typeStr, True, True)
Dim varStr as String = "81db359d-a970-4247-89f8-67995412da35"

All the data types have to be known at compile type, unless you resort
to some /really/ nasty P/Invoke-style coding (Yuk!).

Rather than that, since you will have the Type available at runtime, you
can use Activator.CreateInstance() to instantiate it:

Dim o As Object _
= Activator.CreateInstance( myType )

But, of course, "as Object" is /nowhere/ as useful "as Variant" used to
be...

HTH,
Phill W.

 

[Patrice]

If not yet solved your best bet is likely to explain what you are trying to
do as the code fragment you show doesn't make really sense (for example
casting a variable VarStr to another type and then affecting this variable
to the same variable doesn't make really sense).

You can create a guid using Dim g as new Guid(VarStr) and you can convert
the GUID back to text using the ToString method.