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Previous: 19.17 Win32 ExtensionsChapter 19
Win32 Modules and Extensions
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19.18 OLE Automation

The Win32::OLE modules give Perl support for OLE automation. OLE automation is a Microsoft technology based on COM that allows objects created by another application to be used and manipulated by a program through a common interface.

The application (or DLL) that implements the automation interface is called the automation server. The application that creates and uses the interface is called the automation controller or automation client. Many popular applications expose their objects through automation. Microsoft Word, Excel, and other Office applications can be used as automation servers. Automation is widely used by Active Server Pages (ASP) and CGI scripts to access data repositories, perhaps via ActiveX Data Objects (ADO). You can even use automation to control many development environments and editors.

In order to create an automation object, the server needs to be registered on the system. This is typically done by the server's installation program, but can be done manually using a utility like regsvr32.exe. This involves adding entries to the system registry to tell COM how to find the component, what types of interfaces it provides, what type of server it is, etc. You should be able to find the object model, available methods and properties of the interface in the documentation provided by the application. This object model can be used via Perl's object syntax to create and control objects in your programs.

Four modules provide automation functionality to Perl:

Win32::OLE

Provides the main interface for OLE automation. You can create or open automation objects, use their methods, and set their properties.

Win32::OLE::Enum

Creates objects for collections and defines an interface for enumerating them.

Win32::OLE::Variant

Allows you to convert the Variant data type used in OLE.

Win32::OLE::Const

Imports constants from an automation object into your script.

There are a few limitations to Win32::OLE to note. There is currently no support for OCXs or OLE events (notifications generated by the automation server). Win32::OLE implements the IDispatch interface only, and therefore cannot access a custom OLE interface.

19.18.1 Creating Objects

Automation objects are represented in Perl as instances of Win32::OLE objects. The module provides three constructors for creating objects from a registered automation server.

19.18.2 Automation Methods and Properties

Once you have created an automation object, you can use its methods or adjust its properties as you require. Automation methods are implemented as you'd expect with the Perl object syntax:

$obj->some_method(args);
Automation methods can often take a number of optional parameters. You can pass undef for any unwanted parameters in the arguments list. For example, you can save a WorkBook in Excel with SaveAs. Additional settings allow you to add the WorkBook to the MRU list and create a backup copy:
$xl->WorkBooks(1)->SaveAs($f, undef, undef, undef, undef, 1, undef, undef, 1);
For simplification, you can also use just the named parameters you want to set by passing a reference to a hash containing them. You can do this right in the argument list by creating an anonymous hash reference with {}. The previous example can therefore be written like this:
$xl->WorkBooks(1)->SaveAs($f, {AddtoMru => 1, CreateBackup => 1});
Properties of automation objects are accessed via hash reference notation on the object. For example:
$val = $obj->{"property"};         # get a property value
$obj->{"property"} = $val;         # set a property value
Be aware that properties may not be writable (or even readable). Many automation objects have read-only properties and will generate an exception if you try to write to them. You'll need to consult the documentation for the object to find out which properties you can safely set.

You can enumerate the properties of an automation object using the normal methods for enumerating hashes, which are keys and each. Here's how you can print the properties and values contained within an object:

$xl = Win32::OLE->new('Excel.Application', 'Quit');
while( ($key,$value) = each %$xl ) {
    print "$key=$value\n";
}

19.18.2.1 Win32::OLE methods

Win32::OLE defines a couple of its own methods for dealing with the automation interface. These are not automation-defined methods, although they look the same. If a given method is not defined in Win32::OLE, the method call is dispatched to the automation object. If the method doesn't exist there, you will get an OLE error.

The following methods are defined by Win32::OLE:

19.18.2.2 Win32::OLE functions

The following functions are defined by Win32::OLE. They are not exported by default.

19.18.2.3 Win32::OLE class variables

The Win32::OLE module defines certain class variables that set default behavior for automation usage.

$Win32::OLE::CP

Determines the codepage used by all translations between Perl strings and Unicode strings used by the OLE interface. The default value is CP_ACP, which is the default ANSI codepage. It can also be set to CP_OEMCP, which is the default OEM codepage. Both constants are not exported by default.

$Win32::OLE::LCID

Controls the locale identifier used for all OLE calls. It is set to LOCALE_NEUTRAL by default. Check the Win32 module for other locale-related information.

$Win32::OLE::Warn

Determines the behavior of the Win32::OLE module when an error happens. Valid values are:

0

Ignore error, return undef.

1

Use Carp::carp if $^W is set (-w option).

2

Always use Carp::carp.

3

Use Carp::croak.

The error number and message (without Carp line/module info) are also available through the Win32::OLE->LastError method.

19.18.3 Win32::OLE::Enum

The Win32::OLE::Enum module provides special support for collections. Collections are special automation data types that contain an array of objects or data. A collection supports enumeration - you can iterate through each item through a standard interface.

Collection objects should always provide a Count property (the number of items in the collection) and an Item method. The Item method is used to access a particular collection item using a subscript, which may be an integer or a string, depending on the server. Collection objects may also optionally contain an Add and a Remove method.

Collection objects also support a standard COM interface (IEnumVARIANT) that allows you to enumerate each item in a collection. It defines methods that let you advance the iteration to the next item, skip a given item, restart the enumeration, and create a new copy of the iterator. While all servers are supposed to provide this interface, some servers don't implement all of the methods (often Reset and Clone).

Win32::OLE::Enum defines these methods for enumerating collections. The collection object should provide the Count and Item methods, which are often all you need to use on collections. For example:

$cnt = $coll->Count();
if( $cnt) {
    $obj = $coll->Item(0);
    $obj->do_something();
}
Count will tell you how many items are in the collection, and Item will return the desired item as a Win32::OLE object.

For the enumeration methods, you need to create an enumeration object for the collection object:

$coll = $obj->some_coll();
$enum = Win32::OLE::Enum->new($coll);
Now you can use the enumeration methods on the object.

19.18.3.1 Win32::OLE::Enum methods

The following methods are defined in Win32::OLE::Enum:

19.18.4 Win32::OLE::Variant

All automation data has to be coerced into a special type called a Variant. Most of the time, you don't need to worry about explicit type coercion. You just provide your scalar data and the magic of automation takes care of the rest of it. How- ever, there are cases when you want to control the exact type of data you're send- ing to the automation server. The Win32::OLE::Variant module provides access to the Variant data type and lets you control exactly how the data is represented.

A Variant is an OLE data structure that contains a type field and a data field. The flags are implemented in Perl (as are many constants) as subroutines that return an integer value. The table below lists the Variant type flags, along with a brief description of each.

TypeDescription
VT_EMPTY

No value specified. Incidentally, automation does not use VT_EMPTY for empty optional parameters. Rather, it uses VT_ERROR with a value of DISP_E_PARAMNOTFOUND (which isn't exported by Perl: the value in current Win32 SDK headers is 0x80020004).

VT_NULL

A propagating NULL value was specified (not to be confused with a null pointer). This is used for things like the NULL in SQL.

VT_I2A 2-byte integer value.
VT_I4A 4-byte integer value.
VT_R4An IEEE 4-byte real value.
VT_R8An IEEE 8-byte real value.
VT_CYAn automation currency value.
VT_DATEAn automation date value.
VT_BSTRA string value.
VT_DISPATCH

The value contains another automation object.

VT_ERROR

An error code was specified. The type of the error is determined by the actual value. As mentioned earlier, this is used to implement empty optional parameters.

VT_BOOL

A Boolean (true/false) value. If all bits are 1, it's true, if all bits are 0, it's false. Any other value is invalid.

VT_VARIANTThe value contains another Variant.
VT_UNKNOWN

The value contains an IUnknown pointer (the base class of COM objects).

VT_UI1An unsigned 1-byte character.
VT_BYREF

Can be combined with some fields to indicate that the data is being passed by reference, rather than by value.

VT_ARRAY

The value contains an OLE SAFEARRAY (this flag is not currently exported by Perl).

To convert data to a specific variant type, you create a variant object with either the new constructor method or the convenience function Variant:

$vnt = Win32::OLE::Variant->new(type, data);
$vnt = Variant(type, data);
For example, to force a string to be interpreted as a date, create a variant object and set it to the VT_DATE type:
$dt = Variant(VT_DATE, "August 24, 1970");   # create an explicit data type
$sheet->Cells(1,1)->{Value} = $dt;           # set it to a spreadsheet cell

19.18.4.1 Win32::OLE::Variant methods

The following methods are defined by Win32::OLE::Variant for working with Variant data types:

19.18.5 Win32::OLE::Const

While browsing through the documentation for an automation object, you may have come across references to constant values. For example, if you're trying to save an Excel workbook to a different file format, you need to provide a file for- mat constant. Since the server documentation typically provides symbolic con- stants (e.g., xlExcel5 or xlTemplate), we need a way to access those from Perl. This is the purpose of Win32::OLE::Const, which imports the constants from an automation object into your script.

You can either import the constants directly into your namespace as subs that return the constant value, or you can have them returned as a hash reference with the constant name as the key and its value as the value. Here's an example of the former:

use Win32::OLE::Const ("Microsoft Excel");
print "xlExcel5 = ", xlExcel5, "\n";
which produces something like:
xlExcel5 = 39
Here's an example using the Load method to return a hash reference populated with the constants and their values (this produces the same output as the previ- ous example, of course):
use Win32::OLE::Const;

my $constants = Win32::OLE::Const->Load("Microsoft Excel");
print "xlExcel5 = $constants->{xlExcel5}\n";
Notice that, in both cases, we're supplying a regular expression for the name of the type library from which we want to import. Win32::OLE::Const searches the registry for matching type libraries and loads the one with the highest version number (you can override this by supplying the version you want). You can also specify the language you'd like. The parameters (for either Load or Win32::OLE::Const) are the typelib regular expression, the major version number, the minor version number, and the locale (LCID).

You can also provide the Load method with an automation object, which is then queried for its type library. Interestingly, the documentation notes that this seems to be slower than searching the Registry (though neither is really speedy with a large automation server like Excel). Here's an example of that:

use Win32::OLE;
use Win32::OLE::Const;

# create an Excel application object
my $xl = Win32::OLE->new('Excel.Application', 'Quit') ||
  die "Can't create Excel: ", Win32::OLE->LastError;

# import the constants from it 
my $constants = Win32::OLE::Const->Load($xl);
Using Load (to get a hash reference for the constants) may be preferable to importing all of the constants into your namespace. Some automation servers pro- vide a large number of constants (the current version of Excel has some 900+), so importing them into your namespace can clutter things considerably.


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