Dynamic Cast in C#

mehdi62b · March 24th, 2005, 05:39 PM

Jacob,
well,all of your attributes implement IPluginAttribute and then while you want to retrieve your attributes you cast them to IPluginAttribute..and IPluginAttribute should have a definition for Name property..ofcource IPluginAttribute is recognized at compile time

Quote:

quote:Originally posted by jacob

However in order to make this general (since it require a type cast) I had to make the different attributes implement an interface, which I then can use for the cast.

I think you wanted a type cast for your several attributes so that you could be able to have the exact attribute and ...(instead of working on IPluginAttribute)

I think you needed to create the exact attribute not to create a base attribute (IPluginAttribute)

Quote:

quote:Originally posted by jacob

       attribute = (IPluginAttribute)Attribute.GetCustomAttribute(t
            , attributeType);
        // If the attribute is found and the property Name equals
        // what we are looking for the assembly is returned.
        if(attribute != null && attribute.Name.Equals(name))
        {
            this.type = t;
            this.assembly = a;
        }

did I guess your meaning correctly?

_____________
Mehdi.
software student.

jacob · March 25th, 2005, 05:13 AM

Mehdi...

What I am doing with the interface and what I wanted to do with the type given as argument is actually two different things, but seem to solve my problems.

Quote:

quote:I think you wanted a type cast for your several attributes so that you could be able to have the exact attribute and ...(instead of working on IPluginAttribute)

Therefore, the solution done with the interface is not the answer to my original question. I think it is a matter of opinion if the developer like the method argument approach or the interface approach. In kind of a psudo code I have tried to code what I wanted to do underneath.

Code:

public void LoadPluginAttribute(Type attributeType, string name)
{
    ...
    attribute = (attributeType)Attribute.GetCustomAttribute(t, attributeType);
    if(attribute != null && attribute.Name.Equals(name))
    {
        ...
    }
    ...
}

However in order to be able to retrieve the Name property I would have to make the attribute implement some interface anyways. Otherwise it would be a bad implementation.

What I did with the interface now seem to me like a good solution, since I would still have to make an interface for the classes due to the fact that the Name property has to be supported by every class which should be given as argument to the method, and therefore I might as well cast with the interface.

Jacob.

mehdi62b · March 25th, 2005, 02:13 PM

using the interface as you had done is a very good solution..

however you could do some other things,but you know languages like C#
don't support such dynamic abilities.(dynamic cast)

I can't have a method could return different objects with different types,

I had a problem,I wanted to create some dynamic objects at runtime(with the given type) I did something else I created an object with the given type and with ConstructorInfo, EventInfo, FieldInfo, MemberInfo, MethodInfo, ParameterInfo, and PropertyInfo...got the value I wanted..(for example in your case you could make the exact attribute you wanted and then get its desired property at runtime)..

Quote:

quote:Originally posted by paulie100
Instead of casting using something like

(Int32) y

In my app, I won't know that y is Int32 at coding time. That info will be loaded from a file or a database. So, if the string variable t is set to "Int32" to hold the type of y, I want to be able to do something like

(Type.GetType("System."+t)) y

No,C# doesn't support such abilities,C# is a statically typed language and can't return different objects with different types at run time.

_____________
Mehdi.
software student.

dave.dolan · January 3rd, 2006, 12:45 PM

http://www.codeproject.com/csharp/Fa...Properties.asp

It's the answer to all of your troubles, infact, it even has the same syntax you're looking for.

I about crapped when I saw it because I was just debating taking the time to learn this method of emitting so I can build an ORMapper for NON-relational data (yeah I know tough to find documentation on stuff like that out there because everyone uses RDBMS's, but I'm working with an experimental technology that isn't.. ) I'm quite happy with this little snippet.

yohm31 · April 5th, 2006, 09:25 AM

you can do easily dynamic casting and type manipulation with .Net 2.0 and the powerfull GENERICS

see more on http://www.15seconds.com/issue/031024.htm

bmains · September 25th, 2006, 11:37 AM

Hey,

I've been trying to achieve what you are trying to do. I found most of the resources stating to use Activator.CreateInstance() method, available here: http://msdn2.microsoft.com/en-us/lib...einstance.aspx

Brian