C# .net - override existing built-in function + get underlying method code

Apologies if these are extremely basic questions, but let's say I'm using the void Add(T item) function of BlockingCollection:

1) How would I override the Add function, i.e. if I want to add a check at the beginning and then call the base function, is this possible to do, and if so, would the code look something like this?

protected sealed class BlockingCollection<T> : IEnumerable<T>
    {
        protected override void Add(T item)
        {
            // do something here
            // call base blockingcollection add function, something like return base.Add(item)??
        }
    }

2) If instead of calling the base function, I wanted to actually modify the Add code, is there a way to get the underlying code for the Add function? Would I use something such as Reflection? If so, is there any way to get the underlying code without writing my own program and using reflection to get the method code (i.e. ca开发者_开发知识库n I get the underlying method code within the Visual Studio IDE itself without having to write / compile / run code every time I want to get the underlying code of a method?)?

IEnumerable doesn't have an "Add" method; you'd have to implement your own. ICollection does, however!

Also, because IEnumerable/ICollection are interfaces, not classes, there's no existing implmementation for you to override. You have to do that part yourself.

Edit for possible additional extra super duper correctness:

If you're trying to subclass BlockingCollection and you want to do some additional "stuff" before T is added via "Add", you could do it like this:

public class Foo<T> : BlockingCollection<T>
{
    public new void Add(T item)
    {
        base.Add(item);
        base.Add(item);
    }
}

So, this extremely simple implementation will add anything you put into your Foo via "Add" twice.

I hope you are aware that you are creating a brand new BlockingCollection class, you aren't modifying the System.Collections.Concurrent.BlockingCollection<T> class that's part of the BCL.

Actually modifying the library version of BlockingCollection<T>.Add would be quite difficult to say the least. It's distributed as a signed binary, and .NET doesn't provide a detours-style mechanism. Although DynamicMethod allows you to add new methods to existing classes, I don't think you can use it to replace existing methods.

1) Yes, that is the correct way to do what you are asking.

2) You use a decompiler to view source code for a library API you are choosing to override. This is done by you, the human, and not as part of program execution.

Reflection is a bit different. It allows your code to access an API at run time, but does not access nor expose the API's source code. There are a lot of resources out there, but you could start on MSDN.

Update:

Since the method you are overriding is void, you may not change the implementation by returning something. Try this:

protected override void Add(T item)
{
    // do something here
    // call base blockingcollection add function
    base.Add(item);

    // this is unnecessary, but you could do it for giggles
    return;
}

If the original library has allowed you to override Add then the pseudo-code you show is along the right track. You do need a bit of modification though if I understand your question properly.

First, you would create your own class, inheriting the old class and if not already done by the old class implementing the IEnumerable interface. Of course if the old class is "sealed" you will not be able to do this.

protected sealed class MyBlockingCollection<T> : BlockingCollection<T>, IEnumerable<T>
{
    protected override void Add<T>(T item)
    {
    }
}

now marking your class as sealed will prevent anyone from further overriding methods exposed. If the old class is marked sealed, you will not be able to do this.

To see the code, you will need to decompile the library, using a tool which could be easy or difficult depending on the level of obfuscation that may or may not be employed to keep you from doing just that.

Edit: just winging the code, you should check a reference to ensure you have the appropriate syntax for what you are trying to do.