com

COM

COM is an object-oriented wrapper around WIN32OLE. COM makes it easy to add behavior to WIN32OLE objects, making them easier to work with from Ruby.

Usage

Using COM is rather straightforward. There’s basically four concepts to keep track of:

1. COM objects
2. Instantiable COM objects
3. COM events
4. COM errors

Let’s look at each concept separately, using the following example as a base.

module Word end

class Word::Application < COM::Instantiable
  def without_interaction
    with_properties('displayalerts' => Word::WdAlertsNone){ yield }
  end

  def documents
    Word::Documents.new(com.documents)
  end

  def quit(saving = Word::WdDoNotSaveChanges, *args)
    com.quit saving, *args
  end
end

COM Objects

A COM::Object is a wrapper around a COM object. It provides error specialization, which is discussed later and a few utility methods. You typically use it to wrap COM objects that are returned by COM methods. If we take the example given in the introduction, Word::Documents is a good candidate:

class Word::Documents < COM::Object
  DefaultOpenOptions = {
    'confirmconversions' => false,
    'readonly' => true,
    'addtorecentfiles' => false,
    'visible' => false
  }.freeze
  def open(path, options = {})
    options = DefaultOpenOptions.merge(options)
    options['filename'] = Pathname(path).to_com
    Word::Document.new(com.open(options))
  end
end

Here we override the #open method to be a bit easier to use, providing sane defaults for COM interaction. Worth noting is the use of the #com method to access the actual COM object to invoke the #open method on it. Also note that Word::Document is also a COM::Object.

COM::Object provides a convenience method called #with_properties, which is used in the #without_interaction method above. It lets you set properties on the COM::Object during the duration of a block, restoring them after it exits (successfully or with an error).

Instantiable COM Objects

Instantiable COM objects are COM objects that we can connect to and that can be created. The Word::Application object can, for example, be created. Instantiable COM objects should inherit from COM::Instantiable. Instantiable COM objects can be told what program ID to use, whether or not to allow connecting to an already running object, and to load its associated constants upon creation.

The program ID is used to determine what instantiable COM object to connect to. By default the name of the COM::Instantiable class’ name is used, taking the last two double-colon-separated components and joining them with a dot. For Word::Application, the program ID is “Word.Application”. The program ID can be set by using the .program_id method:

class IDontCare::ForConventions < COM::Instantiable
  program_id 'Word.Application'
end

The program ID can be accessed with the same method:

Word::Application.program_id # ⇒ 'Word.Application'

Connecting to an already running COM object is not done by default, but is sometimes desirable: the COM object might take a long time to create, or some common state needs to be accessed. If the default for a certain instantiable COM object should be to connect, this can be done using the .connect method:

class Word::Application < COM::Instantiable
  connect
end

If no running COM object is available, then a new COM object will be created in its stead. Whether or not a class uses the connection method can be queried with the .connect? method:

Word::Application.connect? # ⇒ true

Whether or not to load constants associated with an instantiable COM object is set with the .constants method:

class Word::Application < COM::Instantiable
  constants true
end

and can similarly be checked:

Word::Application.constants? # ⇒ true

Constants are loaded by default.

When an instance of the instantiable COM object is created, a check is run to see if constants should be loaded and whether or not they already have been loaded. If they should be loaded and they haven’t already been loaded, they’re, you guessed it, loaded. The constants are added to the module containing the COM::Instantiable. Thus, for Word::Application, the Word module will contain all the constants. Whether or not the constants have already been loaded can be checked with .constants_loaded?:

Word::Application.constants_loaded # ⇒ false

That concludes the class-level methods.

Let’s begin with the #connected? method among the instance-level methods. This method queries whether or not this instance connected to an already running COM object:

Word::Application.new.connected? # ⇒ false

This can be very important in determining how shutdown of a COM object should be done. If you connected to an already COM object it might be foolish to shut it down if someone else is using it.

The #initialize method takes a couple of options:

• connect: whether or not to connect to a running instance
• constants: whether or not to load constants

These options will, when given, override the class-level defaults.

Events

COM events are easily dealt with:

class Word::Application < COM::Instantiable
  def initialize(options = {})
    super
    @events = COM::Events.new(com, 'ApplicationEvents',
                              'OnQuit')
  end

  def quit(saving = Word::WdDoNotSaveChanges, *args)
    @events.observe('OnQuit', proc{ com.quit saving, *args }) do
      yield if block_given?
    end
  end
end

To tell you the truth this API sucks and will most likely be rewritten. The reason that it is the way it is is that WIN32OLE, which COM wraps, sucks. It’s event API is horrid and the implementation is buggy. It will keep every registered event block in memory for ever, freeing neither the blocks nor the COM objects that yield the events.

Errors

All errors generated by COM methods descend from COM::Error, except for those cases where a Ruby error already exists. The following HRESULT error codes are turned into Ruby errors:

HRESULT Error Code	Error Class
0x80004001	NotImplementedError
0x80020005	TypeError
0x80020006	NoMethodError
0x8002000e	ArgumentError
0x800401e4	ArgumentError

There are also a couple of other HRESULT error codes that are turned into more specific errors than COM::Error:

HRESULT Error Code	Error Class
0x80020003	MemberNotFoundError
0x800401e3	OperationUnavailableError

Finally, when a method results in any other error, a COM::MethodInvocationError will be raised, which can be queried for the specifics, specifically #message, #method, #server, #code, #hresult_code, and #hresult_message.

Pathname

The Pathname object receives an additional method, #to_com. This method is useful for when you want to pass a Pathname object to a COM method. Simply call #to_com to turn it into a String of the right encoding for COM:

Word::Application.new.documents.open(Pathname('a.docx').to_com)
# ⇒ Word::Document

Installation

Install COM with

% gem install com

License

You may use, copy and redistribute this library under the same terms as Ruby itself.

Contributors

• Nikolai Weibull