Late binding to objects... - C# Discussion Boards

30-Jul-02 7:47

How is late binding done in C#? I'd like to allow for the registration of 'pluggins' (used loosly) for an automation tool for Source Safe. IE as I come across a file type, the appropriate class/library which implements the correct interface is loaded and used to process the file...

Andy Smith30-Jul-02 8:34

Andy Smith

30-Jul-02 8:34

your plugins should implement an interface, which means you don't have to late bind anything beyond checking and casting to the interface.

VB implements its latebinding using reflection behind the scenes (InvokeMember i suppose), which you can do manually in c# if you want.

Ryan Cromwell30-Jul-02 8:44

30-Jul-02 8:44

But I don't want to have to recompile the code after each time or create a switch/if for each type

ie I don't want to do this

IVSSCheckout itemHandler;
switch (fileExt) {
case "asp":
IVSSCheckout itemHandler = new ASPHandler(); //tight bind is problem
case "cls":
IVSSCheckout itemHandler = new VBFileHandler();
case "cpp":
IVSSCheckout itemHandler = new VCPPPHandler();
}

I would rather do something parallel to:

className = GetFromRegistry( fileExt )
itemHandler = CreateObject( className )

I could very well be missing something quite simple and fundamental as I have just moved into .Net languages from C++ and VB.

Eric Gunnerson (msft)30-Jul-02 8:54

30-Jul-02 8:54

You won't have to if you use an interface.

Here's what you need to do:

1) Write an interface that describes the add-in.
2) Build it to a separate assembly.
3) Reference that assembly both in your main program and in the add-in.

Then it's merely a matter of loading the assembly, finding all the types that implement the interface, creating an instance, and casting it to an interface.

If you look on http://www.gotdotnet.com/team/csharp, you'll find two examples of doing this.

On the information page, there's an "execution time code generation" section that does something nearly identical to what you want to do (from the loading perspective).

On the main page, there's a column on app domains and dynamic loading that does something similar, though it's delegate based instead of interface based.

Hope that helps.

Ryan Cromwell30-Jul-02 9:04

30-Jul-02 9:04

Thanks a ton... I'll take a look at it those.

Ryan Cromwell30-Jul-02 9:33

30-Jul-02 9:33

That's great. I knew there would be a way to do it. The reflection namespace was what I was looking for.

I'm not worried about memory resident assemblies as they will be unloaded rather quickly, so loading the Assembly via the Load call appears it will give me what I need. Thanks a lot for your quick responses. And these Reynolds people say you Microsoft guys aren't nice to work with... <sarcasm>

Eric Gunnerson (msft)30-Jul-02 9:49

30-Jul-02 9:49

If you don't have the unload/reload issue, it's a *whole* lot easier to avoid appdomains, put the add-in in the same directory as the exe (or a subdir under it), and just use assembly.Load().

The way appdomains work takes a bit of mind-warping to figure out. It's really like running a process on another machine, from the way you deal with things.

leppie31-Jul-02 2:12

leppie

31-Jul-02 2:12

Eric Gunnerson (msft) wrote:
The way appdomains work takes a bit of mind-warping to figure out.

Hi Eric, i have had my mind warped already (partially) Smile | :)

I understand from your article how to use objects from remote domains in the main app domain, but how does it work the other way around?

Eg. You have main program with an object say A. In my case object A also contains a NetworkStream that should not be disconnected. I want to now load/unload "helper" assmeblies in a remote domain that can reference an instance of object A in the main app. Can this be done, without me landing up in a psychiatric ward? Eek! | :eek:

Reading both parts of the graphing calculator article was already a great help, i cant find any examples on how to do the reverse as described above.

Thanking you in advance

Cheers

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Eric Gunnerson (msft)31-Jul-02 6:48

Why does OleDbDataAdaptor do this?

31-Jul-02 6:48

I think the way you'd do this would be to pass a MarshalByReference object as a parameter to the other app domain when you made a call. That should result in the other app domain having a proxy object to the object in the main app domain.

I haven't tried this, however.

Zombies with Coffee, LLC30-Jul-02 5:51

Zombies with Coffee, LLC

30-Jul-02 5:51

Really curious why the 'where' statements that the OleDbDataAdaptors creates are excessively wordy...

What are they trying to accomplish here? Do automatic code creators get paid by the line? What is the point of the extra 250 lines of code?

Wouldn't just WHERE (CustomerID=?) work just fine?
WTF | :WTF:

this.oleDbDeleteCommand1.CommandText = @"DELETE FROM Customers WHERE (CustomerID = ?) AND (Address = ? OR ? IS NULL AND Address IS NULL) AND (City = ? OR ? IS NULL AND City IS NULL) AND (CompanyName = ?) AND (ContactName = ? OR ? IS NULL AND ContactName IS NULL) AND (ContactTitle = ? OR ? IS NULL AND ContactTitle IS NULL) AND (Country = ? OR ? IS NULL AND Country IS NULL) AND (Fax = ? OR ? IS NULL AND Fax IS NULL) AND (Phone = ? OR ? IS NULL AND Phone IS NULL) AND (PostalCode = ? OR ? IS NULL AND PostalCode IS NULL) AND (Region = ? OR ? IS NULL AND Region IS NULL)";<br />

And the parameter list...

this.oleDbDeleteCommand1.Parameters.Add(new System.Data.OleDb.OleDbParameter("Original_Address", System.Data.OleDb.OleDbType.VarWChar, 60, System.Data.ParameterDirection.Input, false, ((System.Byte)(0)), ((System.Byte)(0)), "Address", System.Data.DataRowVersion.Original, null));<br />
this.oleDbDeleteCommand1.Parameters.Add(new System.Data.OleDb.OleDbParameter("Original_Address1", System.Data.OleDb.OleDbType.VarWChar, 60, System.Data.ParameterDirection.Input, false, ((System.Byte)(0)), ((System.Byte)(0)), "Address", System.Data.DataRowVersion.Original, null));<br />
<br />
... x 10 times more

Re: Why does OleDbDataAdaptor do this?

Zombies with Coffee, LLC30-Jul-02 6:18

Zombies with Coffee, LLC

30-Jul-02 6:18

Ahhh... Optimistic Concurrency. Nevermind.

implicit cast

Christian Graus30-Jul-02 4:23

Christian Graus

30-Jul-02 4:23

Is it possible to create a class, call it a, and make it implicity accept a reasonable cast, for example

string s = MyA;

???

I was thinking of writing a class called ConstString, for example, passing a string into the constructor, and then having it return the string when the object was used as a string. So I could do this

public void MyFunc (ConstString s)

and call it like this

MyFunc(ConstString(myString));

Oh, and if anyone reading has an answer to my XmlTextWriter problem from yesterday, it's still driving me mad.....

Thanks.

Christian

We're just observing the seasonal migration from VB to VC. Most of these birds will be killed by predators or will die of hunger. Only the best will survive - Tomasz Sowinski 29-07-2002 ( on the number of newbie posters in the VC forum )

Nish Nishant30-Jul-02 5:23

Nish Nishant

30-Jul-02 5:23

Christian Graus wrote:
Is it possible to create a class, call it a, and make it implicity accept a reasonable cast, for example

string s = MyA;

???

using System;

class Nish
{
	public static void Main()
	{
		string s = new Nish("Christian Graus");
		Console.WriteLine(s);
	}

	public Nish(string s)
	{
		m_s = s;
	}

	public static implicit operator string(Nish a)
	{
		return a.m_s;
	}
	private string m_s;
}

Author of the romantic comedy

Summer Love and Some more Cricket [New Win]

Review by Shog⁹
Click here for review[NW]

Christian Graus30-Jul-02 12:27

Christian Graus

30-Jul-02 12:27

Thanks - looks like I win and C# loses. It's such a shame to find myself fighting the language.

Christian

We're just observing the seasonal migration from VB to VC. Most of these birds will be killed by predators or will die of hunger. Only the best will survive - Tomasz Sowinski 29-07-2002 ( on the number of newbie posters in the VC forum )

James T. Johnson30-Jul-02 16:22

James T. Johnson

30-Jul-02 16:22

You don't need to do that for a string object. strings are immutable so no changes can be made to it.

All methods on string that would do any modification return a new string object containing the changes.

James
"Java is free - and worth every penny." - Christian Graus

Christian Graus30-Jul-02 17:17

Christian Graus

30-Jul-02 17:17

Thanks - I know that, I just wrote the first example that sprang to mind. The object I actually want to pass is an XmlNode, and I dunno that this will help, because once I get back the node, I can still call methods on it that change it.

Christian

We're just observing the seasonal migration from VB to VC. Most of these birds will be killed by predators or will die of hunger. Only the best will survive - Tomasz Sowinski 29-07-2002 ( on the number of newbie posters in the VC forum )

DLL Hell

gekoscan30-Jul-02 2:38

gekoscan

30-Jul-02 2:38

I am trying to use a library file that I created in MFC Visual C++. It
won't let me include it as a reference so I am assuming I need to do
something like this:

[DllImport("MyDLL.dll")]
private static extern bool Counter(out long lpCount);

However I don't just wanna import a method I wanna make an instance of the
class which is called CAppBar. Can anyone point me in the write direction
here? It would be a huge help thanks...

Big Grin | :-D

Re: DLL Hell

Eric Gunnerson (msft)30-Jul-02 8:48