COM Extensions to AutoIt

A short introduction

What is COM?

COM stands for "Component Object Model". It is the Microsoft way to interconnect software using a common interface. These interfaces are defined in a COM Object.

Before COM, you had to know the exact implementation of a program before you could 'interface' with it. Using COM, you can now "talk" to its defined Object(s). The only things you have to know are the names of the Objects that are used and which 'properties' or 'methods' they have.

What are (Object) properties or methods?

These are the two basic characteristics of an Object. You can see a 'property' as the data storage of an Object. A 'method' can be seen as an internal function call to do something with the data.

Do I need COM in my AutoIt script?

It just depends. AutoIt has a lot of built-in functions and a huge library of UDF's. You can do most of your programming with these. However if you need special 'interfacing' to other applications, using COM might save you some lines of script. Scripters have to be aware that the existence of COM Objects depend HEAVILY on the Operating System AND the installed software. The examples below have all been tested under a 'plain' Windows XP professional version with Microsoft Office 2000.

An example usage of COM in AutoIt

Let's say you want to minimize all open windows. You could do this using regular AutoIt functions like WinList and WinSetState. However, two lines of COM-code can give you the same result:

Side note: The example is no longer the shortest way to minimize all windows after the introduction of the WinMinimizeAll() function in AutoIt.

On the first line we create a new object called "shell.application". This is an internal Windows object, defined in shell32.dll. The pointer to this new object is assigned to the variable $oShell. $oShell is from now on an Object variable.

On the second line, we use a Method called "MinimizeAll" to the oShell object. This will minimize all windows.

All Windows versions have a huge amount of internal Objects for various purposes. And applications like Excel or Word have also their own set of Objects.

However, it is sometimes difficult to get a list of all existing Objects defined on your system with their corresponding properties and methods. Searching at Microsoft.com or Google.com might give you some clues about the Object 'X' you want to use.

For instance, you can find information about the "shell.application" object at:
http://msdn.microsoft.com/en-us/library/bb774094.aspx

To get a peek on all objects currently installed on your system, the "OLE/COM Object Viewer" is a very helpful tool. This tool will be explained in a separate section below.

Let's do another example. We would like to get a HTML source code from a certain web page. You could use the internal InetGet() function to save the result to a file and retrieve it back again with FileRead(). But these lines of code do the same:

The (string) variable $HTMLSource now contains the complete HTML code of the AutoItScript.com home page (that is, the top HTML-Frame).

(Information about the "winhttp.winhttprequest" object can be found at:
http://msdn.microsoft.com/en-us/library/aa384106.aspx )

Please mind this: The existence of Objects depend on the computer's operating system and installed programs. For example, the winhttp.winhttprequest.5.1 object only exists on computers that have at least Internet Explorer version 5 installed. When you are sharing scripts that use COM objects, be sure the objects exist on all computers.

Object variables behave a bit different than other types of AutoIt variables. An Object is not a real value, but a 'pointer' to something outside the script. So you can't perform arithmetic's, nor equations on Object variables. When you assign an Object variable a different value, the 'pointer' will automatically be released. You can, for instance, force deletion of an Object by assigning it any number or any text value.

You don't need to delete Objects when you are finished. If a script exits, AutoIt tries to release all active references to Objects that had been created in the script. Same thing happens when you had defined a local Object variable inside a function, and the function ends with a return.

Automation using COM

A very popular application of COM is to 'automate' programs. Instead of using the regular AutoIt functions like Send() or WinActivate(), you can make use of the Objects that are defined inside the program.

Here is an example that 'automates' Microsoft Excel:

The complexity of controlling other programs depends on that specific program, not on the AutoIt script. If something does not work as expected you might need to consult the applications' documentation and not the AutoIt help.

Special Statements

In AutoIt, two special statements are designed for COM usage:

With/EndWith and the For/In/Next loop.

With..EndWith

The With/EndWith statement does not add functionality, but it makes your script easier to read. For instance, the previous example using Excel can also be written as:

This example does not save you a lot of text, but when your object uses long lines of properties/methods, you can shorten it heavily within a With statement.

For..In

The FOR...IN loop is required when using Collections. Collections are a special type of Object, that exist out of multiple sub-Objects. You could see them as Arrays (Actually, the For..In statement also works on Array-type variables).

For..In loop using an Array

Below is an example of an For..In loop. This example uses a normal AutoIt array, so it has nothing to do with COM. It's just to show you the principle: