Programming Ruby

The Pragmatic Programmer's Guide

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Microsoft Windows Support

The three libraries documented in this chapter turn Ruby into a powerful and convenient Windows scripting language. Now you have the power to control your applications, but in a controlled, object-oriented environment.

class WIN32OLE
Parent: Object
Version: 1.6


connect const_load new [ ] [ ]= each invoke

require 'win32ole'
ie ='InternetExplorer.Application')
ie.visible = true

WIN32OLE provides a client interface to Windows 32 OLE Automation servers. See the tutorial description on page 164 for more information.

WIN32OLE::VERSION Current version number

class methods
connect WIN32OLE.connect( aString ) -> wapi

Returns a new OLE automation client connected to an existing instance of the named automation server.

const_load WIN32OLE.const_load( wapi, [ aClass=WIN32OLE ] ) -> nil

Defines the constants from the specified automation server as class constants in aClass.

new aString ) -> wapi

Returns a new OLE automation client connected to a new instance of the automation server named by aString.

instance methods
[ ] wapi[ aString ] -> anObject

Returns the named property from the OLE automation object.

[ ]= wapi[ aString ] = aValue -> nil

Sets the named property in the OLE automation object.

each wapi.each {| anObj | block }

-> nil

Iterates over each item of this OLE server that supports the IEnumVARIANT interface.

invoke wapi.invoke ( aCmdString, [ args ]* ) -> anObject

Invokes the command given in aCmdString with the given args. args may be a Hash of named parameters and values. You don't need to call invoke explicitly; this class uses method_missing to forward calls through invoke, so you can simply use the OLE methods as methods of this class.

Parent: Object
Version: 1.6


message_loop new on_event

This (slightly modified) example from the Win32OLE 0.1.1 distribution shows the use of an event sink.

require 'win32ole'

$urls = []

def navigate(url)   $urls << url end

def stop_msg_loop   puts "IE has exited..."   throw :done end

def default_handler(event, *args)   case event   when "BeforeNavigate"     puts "Now Navigating to #{args[0]}..."   end end

ie ='InternetExplorer.Application') ie.visible = TRUE ie.gohome ev =, 'DWebBrowserEvents')

ev.on_event {|*args| default_handler(*args)} ev.on_event("NavigateComplete") {|url| navigate(url)} ev.on_event("Quit") {|*args| stop_msg_loop}

catch(:done) {   loop {     WIN32OLE_EVENT.message_loop   } }

puts "You Navigated to the following URLs: " $urls.each_with_index do |url, i|   puts "(#{i+1}) #{url}" end

WIN32OLE_EVENT is used in conjunction with the WIN32OLE class to add callbacks for Windows 32 events.
class methods
message_loop WIN32OLE_EVENT.message_loop -> nil

Executes the Windows event loop, translating and dispatching events.

new ( anOle, aName ) -> wapi

Returns a new WIN32OLE_EVENT (an event sink) for the given WIN32OLE object and named event source. If aName is nil, it will attempt to use the default source and will raise a RuntimeError if it cannot find one.

instance methods
on_event wapi.on_event ( [ anEvent ] ) {| args | block }

-> nil

Defines a callback for the named anEvent. If anEvent is nil, then this callback is associated with all events. The block will be given any arguments appropriate for this event.

class Win32API
Parent: Object
Version: 1.6


new call Call

This example is from the Ruby distribution, in ext/Win32API:

require 'Win32API'

getCursorPos ="user32", "GetCursorPos", ['P'], 'V')

lpPoint = " " * 8 # store two LONGs getCursorPos.Call(lpPoint) x, y = lpPoint.unpack("LL") # get the actual values

print "x: ", x, "\n" print "y: ", y, "\n"

ods ="kernel32", "OutputDebugString", ['P'], 'V') ods.Call("Hello, World\n")

GetDesktopWindow ="user32", "GetDesktopWindow", [], 'L') GetActiveWindow ="user32", "GetActiveWindow", [], 'L') SendMessage ="user32", "SendMessage", ['L'] * 4, 'L') SendMessage.Call(GetDesktopWindow.Call, 274, 0xf140, 0)

The Win32API module allows access to any arbitrary Windows 32 function. Many of these functions take or return a Pointer datatype---a region of memory corresponding to a C string or structure type.

In Ruby, these pointers are represented using class String, which contains a sequence of 8-bit bytes. It is up to you to pack and unpack the bits in the String. See the reference section for unpack on page 378 and pack on page 286 for details.
class methods
new dllname, procname, importArray, export ) -> wapi

Returns a new object representing a Windows 32 API function. dllname is the name of the DLL containing the function, such as ``user32'' or ``kernel32.'' procname is the name of the desired function. importArray is an array of strings representing the types of arguments to the function. export is a string representing the return type of the function. Strings ``n'' and ``l'' represent numbers, ``i'' represent integers, ``p'' represents pointers to data stored in a string, and ``v'' represents a void type (used for export parameters only). These strings are case-insensitive.

instance methods
call [ args ]* ) -> anObject

Calls this API function with the given arguments, which must match the signature specified to new.

Call wapi.Call( [ args ]* ) -> anObject

Synonym for Win32API#call.

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at

Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder.

Distribution of the work or derivative of the work in any standard (paper) book form is prohibited unless prior permission is obtained from the copyright holder.