Why use DLLs?

  • Thread starter Thread starter Florian
  • Start date Start date
F

Florian

Hi,

I have a question regarding Application Development and the usage of
DLLs. Because my EXE is growing I'm not sure if I should put some code
into a DLL. But what kind of code should I put there? In my
unserstanding it only make sense for code wich isn't often used. At
which size does it make sense?
thx
 
Florian said:
I have a question regarding Application Development and the usage of
DLLs. Because my EXE is growing I'm not sure if I should put some code
into a DLL. But what kind of code should I put there? In my
unserstanding it only make sense for code wich isn't often used. At
which size does it make sense?
Click to expand...

On the contrary - libraries are ideal for code which *is* often used -
by different applications. If you have two applications, both of which
want to use a bunch of the same classes, you can put those classes in a
library, and both applications can reference the same library.
 
Jon Skeet said:
On the contrary - libraries are ideal for code which *is* often used -
by different applications. If you have two applications, both of which
want to use a bunch of the same classes, you can put those classes in a
library, and both applications can reference the same library.
Click to expand...

In addition to that, DLL's also help structuring an application: You can
develop and test them separately (maybe by separate people, too).
Maintainance is also often easier, as responsibilities between different
assemblies (DLL's and EXE's) are clearer.

And, DLL's are also often used for optional code parts: If a certain feature
is only needed by some of your customers, you can put it into a DLL, and (if
the DLL is loaded dynamically) deploy that DLL only on PCs where it's
needed.

Niki
 
My design philosophy is that almost all code should go in a DLL and that the
EXE would contain minimal logic. The best EXE will have only a simple main
function that processes the commandline arguments and passes that
information to classes from the library.
 
Florian,
As Peter suggested, my EXE's tend to be smaller, while most of the actual
"program" logic is in various DLLs. Which may or may not be shared across
applications.

Normally my DLL's follow the logical tiers of my application.

For example:

MyApp.Exe
MyApp.Framework.dll
MyApp.Plugin1.dll
MyApp.Plugin2.dll
MyApp.Data.dll
MyApp.UI.dll
MyApp.SomeSubSystem.dll
...


Another example: I have a Windows Service that is organized as:

MyApp.Manager.exe (a Windows Forms Program)
MyApp.Service.exe (a Windows Service)
MyApp.Framework.dll (a class library)

The Server & Manager both call into the Framework to perform actions.

Hope this helps
Jay
 
I have to agree too, keep your interface as lightweight as possible and put
your business logic in a business layer. Its the principle of multi-tiered
applications and you'll reap the benefits in the long run. That said,
sometime its quicker and cheaper to hack your code into a single exe if you
cant think of a scenario in your environment where you might need
reusability.

--
Regards

John Timney
ASP.NET MVP
Microsoft Regional Director
 
I have a question regarding Application Development and the usage of
DLLs. Because my EXE is growing I'm not sure if I should put some code
into a DLL. But what kind of code should I put there? In my
unserstanding it only make sense for code wich isn't often used. At
which size does it make sense?
Click to expand...

You can easily leave it as it is - unless you have a dozen or so
different apps that would all be using the same code (in that case,
put all the common code into one or multiple DLL's).

Having DLL's can achieve two main things:

* Reduce the code size (on disk) by sharing common code amongst
applications - not such a great issue anymore with multi-gigabyte
harddisks

* Make apps more easily maintainable, since you might be able to
upgrade some of the app's functionality by simply replacing a DLL (or
multiple DLLs) that contain the code implementing the functionality.

Also, using a DLL-based plugin system can make your app more easily
extensible.

But all in all, if you have just basically one app and don't need
dynamic extensions, you can easily leave everything in one big EXE.

Marc

================================================================
Marc Scheuner May The Source Be With You!
Bern, Switzerland m.scheuner(at)inova.ch
 
Hi,
thx for the answers. Does that mean that a DLL should be written for
every logical part (namespace) in an application? Isn't there a big
overhead for dll loading? So If I write a application with DB Access I
have all the classes for the Datamodel in a DLL ,a DLL for the DB
Access and a DLL for the GUI, when all the Layers are on the Client?

thx again
Florian
 
Florian said:
Hi,
thx for the answers. Does that mean that a DLL should be written for
every logical part (namespace) in an application?
Click to expand...

This is really largely a matter of taste, but it's not uncommon.
Isn't there a big overhead for dll loading?
Click to expand...

No. Loading code from an EXE file or from an DLL file shouldn't make any
difference.

Niki
 
thx for the answers. Does that mean that a DLL should be written for
every logical part (namespace) in an application?
Click to expand...

No, I wouldn't create a DLL for every namespace - I would create a DLL
for every logically separate part of your app, especially those which
you might want to extend dynamically (e.g. import filters on a
graphics display program etc.). We normally create separate DLL's for

* database access
* business logic layer
* UI code
* utility / shared code

plus a main app's EXE tying everything together.

MArc
================================================================
Marc Scheuner May The Source Be With You!
Bern, Switzerland m.scheuner(at)inova.ch
 
Hi,
Sorry to poke my nose in the conversation…
I am doing exactly the same splitting things up as …
< *database access
* business logic layer
* UI code
* utility / shared code
Click to expand...

But, I am developing a large application which currently holds about
100 forms in the UI(I think its going to get 200 forms in total) I do
reuse the forms when ever possible. Right now my application exe size
is 2.5 MB.

So I need to know is it *Bad* to have big exe? If so how to reduce it?
I thought of splitting the UI into the multiple dlls but, it's not
possible as the forms need to communicate with each other.

I would appreciate any feedback or suggestions

Thanks

RK
 
Raj said:
Hi,
Sorry to poke my nose in the conversation.
Click to expand...

This is a public newsgroup. I always thought anyone was invited to post
here?
I am doing exactly the same splitting things up as .
< *database access

But, I am developing a large application which currently holds about
100 forms in the UI(I think its going to get 200 forms in total) I do
reuse the forms when ever possible. Right now my application exe size
is 2.5 MB.

So I need to know is it *Bad* to have big exe?
Click to expand...

It certainly needs more memory, but splitting it into DLLs wouldn't change
that. Things don't get inefficient or something like that (to the best of my
knowledge), if that's what you meant.
If so how to reduce it?
Click to expand...

Reduce redundancy. Hard to give you any better advice without facts. Given
the number of 200 forms, maybe it would be efficient to build some kind of
generic data-input (or whatever) form that can be reused heavily (e.g. you
could populate it by using reflection, inserting an appropriate control for
each member in a class?)

Niki
 
Thanks Niki for the feedback

Currently i have about 100 forms, i am assuming that it could reach
200 figure!
All these forms have been reused multiple times so i do not think that
is an option now.
Only idea behind the reducing the size being easy updates(Physical
transfer of files) on all the clients.
I am thinking since my application is an intranet application i should
build some kind of auto update feature to the application(some thing
like a Microsoft's smart client), so that this contraint will be
minimized
I know if i tried to build a dll for each of my forms its going to be
bigger mess than ever trying to manage components individually.

Thanks again
Raj
 
Right now my application exe size is 2.5 MB.
So I need to know is it *Bad* to have big exe?
Click to expand...

No - Windows will only load whatever parts it actually needs - it
won't load the whole EXE into memory (as long as you don't poke around
it with e.g. EXE compressors etc.).

So it might be a problem in terms of deployment (you need to copy out
your 2.5 MB EXE file to all your customers, whenever there's an
update), but other than that, and especially at runtime, there's no
significant drawback to having a large EXE file.

Marc

================================================================
Marc Scheuner May The Source Be With You!
Bern, Switzerland m.scheuner(at)inova.ch
 
Back
Top