How to dynamically add propery in a Class in C#?

coolcoder2007 · #1 (**permalink**) December 23rd, 2008, 01:00 AM

Hi All,

I need to create property in a class dynamically.
Property names will come from database and also the total number of properies can be changed according to database value.
I have tried with CodeDome,but unable to solve.

Please suggest me.

Old Pedant · #2 (**permalink**) December 23rd, 2008, 01:09 AM

If you mean a simple data member of a class, much as you would do by coding

Code:

class Foo 
{
    int someProperty;
}

the answer is simple: You can't. You can't. You can't.

C#--along with C++ and VB.NET and C and Java and Pascal and many other languages--is a *COMPILED* language. Generally speaking, only INTERPRETED languages allow adding members to classes dynamically.

However...

However, if you want to plan ahead, you could clearly add a data member to your class that is, say, some kind of collection. And then you can add elements to that collection.

Depending on the rest of your code, this might be exactly what you need.

In fact, if your class includes, say, a DataTable member (or DataSet member), then you have accomplished what you are after already.

But *compiled*? No.

coolcoder2007 · #3 (**permalink**) December 23rd, 2008, 02:23 AM

Thanks a lot for your quick reply.

But could u plz explian this line
"However, if you want to plan ahead, you could clearly add a data member to your class that is, say, some kind of collection. And then you can add elements to that collection."

Means i need some example code.

Old Pedant · #4 (**permalink**) December 23rd, 2008, 03:43 AM

If you have *ANY* kind of collection object as a member of your class, then you could add to it as needed.

Example: Say you have a class that describes these "properties" that you want to dynamically add. Maybe a property has a name, a type, and a value. For simplicity, we'll say that the value is held as just an Object and you will write code to cast the various values to their correct types.

Code:

class MyProperty
{
    public String name;
    public DataTypeDescriptor type;
    public Object value;
}

(I'm keeping this simple, just making everything public. In "real life" you'd probably write get/set methods and keep the data members private. But that's really just syntactic sugar.)

Okay, so now you write your class that needs to be able to hold an arbitrary number of these dynamically added MyProperty objects.

Code:

class MyHolder
{
    // I'm just making up some other members of the class...
    public DateTime whenCreated; 
    public int timeToLive;
    public String password; // silly stuff

    // but then here is your collection:
    List<MyProperty> properties;

    // and you could have methods such as
    void AddProperty( MyProperty toAdd )
    {
        properties.Add( toAdd );
    }
    // or maybe:
    void AddProperty( String nm, DataTypeDescriptor dtd, Object val );
    {
        // really should have a constructor for MyProperty, but even without one
        // we can do it the brute force way:
        MyProperty prop = new MyProperty( );
        prop.Name = nm;
        prop.Type = dtd;
        prop.Value = val;
        properties.Add( prop );
    }
    // and much much more...
}

If you think about it, the .NET framework is just chock full of collections such as this. Just as one for-instance, DataReader and DataTable and DataRow objects are all implemented, under the covers, with some kind of collection. And of course when you use a method such as FindControl( ), you are really just looking for a particular object in the collection of objects that represent the HTML display. And and and...

At this point, maybe the best thing I can suggest is that you think about buying and reading this book:
http://www.wrox.com/WileyCDA/WroxTit...470261293.html

It's probably the best way to approach C#, much better than starting from building websites, I think. And it's going to cover these kinds of subjects in a lot more depth than anyone can, just posting messages in these silly little windows.

coolcoder2007 · #5 (**permalink**) December 23rd, 2008, 05:20 AM

thanks a lot for your help....
I'll try this.

joefawcett · #6 (**permalink**) December 23rd, 2008, 07:57 AM

It can be done using reflection and code emission, or possibly with extension methods to some xtent. You'd have to describe the scenario and it's complicated. Probably better off having a DynamicProperties property as the others have suggested.

planoie · #7 (**permalink**) December 23rd, 2008, 11:28 AM

coolcoder2007 -

Could you explain what you are trying to achieve, versus how you are trying to achieve it? Perhaps there is a more logical solution to what you are trying to do instead of us trying to help you implement how you think you should solve the original problem.

There are solutions for building code on the fly and compiling then consuming it, however, without a clearly stated problem, that may or may not be the appropriate solution.

Old Pedant · #8 (**permalink**) December 28th, 2008, 05:55 PM

Peter wrote: "There are solutions for building code on the fly and compiling then consuming it..."

I hadn't thought about it enough, I guess, but I can see that you could easily enough do that with ASP.NET. You just spit out ".aspx" files and then transfer to your dynamically created pages and presto.

But man oh man, I'd sure hate to try to maintain and debug such a system. Ugh, to say the least.

alenwu · #9 (**permalink**) January 5th, 2009, 09:29 PM

DaoMappingTool will connect your database and generate fully working extendable source code for DAO classes.

Google it and download to have a try.

Need to download code?

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