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What is ActiveX Com ?

Can experts tell me what is really ActiveX Com ?
Is it different than ActiveX DLL and ActiveX Control ?
Please explain to me in a very plain english, so
I can understand. Thanks !
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tryforum
Asked:
tryforum
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Arthur_WoodCommented:
COM is short for Component Object Model (COM) which is the structure that Microsoft developed to enable components (building blocks of programs, like Textboxes, and Buttons, and classes) to be developed in a standard way, so that they could be used, just like building blocks, to build larger programs out of smaller, standard pieces.

ActiveX is the name that Microsoft then gave to the technology which allows those component to communicate with each other.  It is a more advnaced version of a technology that Microsoft developed several years ago, which was known as OLE (Object Linking and Embedding).

A DLL is an Dynamic Link Library, and is one of the pieces of COM, as is an ActiveX Control.

Arthur Wood
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AmitabhCommented:
Well,
Though things have been very well explained above, would like to add further to make the topic more clear to you.

The objective is reusability, like if a handle of the car gets damaged u don't replace a whole car but only a handle.

COM is a technology specifications developed by Microsoft so that the components developed in different COM compliant languages can be used across platforms.

ActiveX is the name given to a technology which implements COM. Arthur has described it well, above.

Regards
A.Pandey
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AmitabhCommented:
There are basically three types of COM Components

ActiveX DLL
ActiveX Exe
ActiveX Control

ActiveX DLL is a component which does a particular job but don't have a user interface and hence it is used in the client's process space.

ActiveX exe differs with the DLL in the way that it runs in an independent process space and not one of client's. hence when the DLL breaks the client application also crashes but when an ActiveX Exe breaks Client application has no effect.

ActiveX control is a component with a user interface with which user can interect.



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priya_pbkCommented:
hi tryforum,

Both Arthur_Wood and Amitabh has given you a good explaination. Let me try in a very simplified way, ie simple english without much jargons.

ActiveX COM:
Branded by Microsoft as ActiveX COM. This means MS has given you the convience of making your own controls with the help of the existing conrols.
eg:
If you want to create a text box which should either take number data or string data or alhpa numeric ie (numbers and string), you can create this with the help of ActiveX COM project, rather than writing code in each of the textbox's keypress/keydown event.
Do'nt you feel it would be nice to have a control which you can design according to your requirements, do the coding once and use it across the various projects.

ActiveX DLL:
ActiveX DLL are those projects wherin you can write your code of various functions and procedures which you might want to use from time to time.
eg: Recently I had made a dll which had a function which takes an array of numbers and string as parameter for sending SMS to users.
I could have done the sending SMS part in the VB project itself, but whenever i had to send an sms i just need to reference that DLL in my project and call the function to send sms.

Also one of difference between ActiveX COM and ActiveX dll is that the former has a visual interface so that the author of the UserControl(ie the person who is making the ActiveX control) can place his different controls on that designer form, whereas since the DLL has just the functions and procedures, it does not have a visual interface.

To use this both, you have to Make it, ie ->File, Make .ocx or .dll and use/reference it in your projects.

Hope I could help you to get a better picture!

-priya

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