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Programming Ruby The Pragmatic Programmer's Guide |
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Ruby and Microsoft Windows
Ruby is written for POSIX environments, which means that it can
take advantage of all of the system calls and libraries
that Unix programmers are familiar with.
But there are a number of features and extensions designed to make
Ruby more useful in a Microsoft Windows environment, too. In this
chapter, we'll look at these features and share some secrets to using
Ruby effectively under Windows.
Windows does not provide a POSIX environment by itself, so some sort
of emulation library is required in order to provide the necessary
functions. There are several ports of Ruby for
Windows: the most commonly used one relies on the GNU Win32
environment, and is called the ``cygwin32'' port. The cygwin32 port
works well with extension libraries, and is available on the Web as a
precompiled binary.
Another port, ``mswin32,'' does not rely on cygwin. It is currently
available as source code only. The remainder
of this chapter will refer to the cygwin32 port.
There are two executables provided with the cygwin32 Ruby distribution: ruby.exe and rubyw.exe.
ruby.exe is meant to be used at a command prompt (a DOS shell),
just as in the Unix version. For applications that read and write to
the standard input and output, this is fine.
But that also means that anytime you run ruby.exe, you'll get a
DOS shell even if you don't want one---Windows will create a new
command prompt window and display it while Ruby is running. This
might not be appropriate behavior if, for example,
you double-click on a Ruby script that uses a graphical interface
(such as Tk), or if you are running a Ruby script as a background
task, or from inside another program.
In these cases, you'll want to use rubyw.exe. It is the same as ruby.exe except that it does not provide standard in, standard
out, or standard error, and does not launch a DOS shell when run.
You can set a file association[Using View/Options/Filetypes from Explorer.]
so that files with the extension ``.rb'' will
automatically use rubyw.exe. By doing this, you can double-click
on Ruby scripts and they will simply run without popping up a DOS
shell.
If you plan on doing Ruby programming that needs to access
some Windows 32 API functions directly, or to use the entry points in some
other DLLs, we've got good news for you---the Win32API extension.
The Win32API module is documented beginning on page 508,
but here's a quick peek at how it works.
You create a Win32API object that represents a call to a
particular DLL entry point by specifying the name of the function, the
name of the DLL that contains the function, and the function signature (argument
types and return type). The resulting object can then be used to make
the function call.
Many of the arguments to DLL functions are binary structures
of some form. Win32API handles this by using Ruby String
objects to pass the binary data back and forth. You will need to pack
and unpack these strings as necessary (see the example
on page 508).
If groveling around in the low-level Windows API doesn't interest you,
Windows automation might---you can use Ruby as a client for Windows
Automation thanks to a Ruby extension called WIN32OLE, written by
Masaki Suketa.
The examples in this section are taken from those
provided in the WIN32OLE distribution.
Windows automation
allows an
automation controller (a client) to issue commands and queries against
an automation server, such as Microsoft Excel, Word, PowerPoint, and
so on.
You can execute a method of an automation server by calling a method
of the same name from a WIN32OLE object. For instance, you can
create a new WIN32OLE client that launches a fresh copy of
Internet Explorer and commands it to visit the home page.
ie = WIN32OLE.new('InternetExplorer.Application')
ie.visible = true
ie.gohome
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Methods that aren't known to WIN32OLE (such as visible or gohome) are passed on to the WIN32OLE#invoke method, which sends the
proper commands to the server. The WIN32OLE reference
beginning on page 505 describes the class in detail, but
we'll go over a few of its features here.
You can set and get properties from the server using normal
Ruby hash notation. For example, to set the Rotation property
in an Excel chart, you might write
excel = WIN32OLE.new("excel.application")
excelchart = excel.Charts.Add()
...
excelchart['Rotation'] = 45
puts excelchart['Rotation']
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An OLE object's parameters are automatically set up as attributes of
the WIN32OLE object. This means that you can set a parameter by
assigning to an object attribute.
excelchart.rotation = 45
r = excelchart.rotation
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Because these attributes are conventional Ruby accessor
methods, attribute names cannot start with a capital letter.
In this example, we have to use rotation instead of Rotation.
Other automation client languages such as Visual Basic have the
concept of named arguments. Suppose you had a Visual Basic
routine with the signature:
Song(artist, title, length): rem Visual Basic
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Instead of calling it with all three arguments in the order specified,
you could use named arguments.
Song title := 'Get It On': rem Visual Basic
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This is equivalent to the call Song(nil, 'Get It On', nil).
In Ruby, you can use this feature by passing a hash with the named
arguments.
Song.new( 'title' => 'Get It On' )
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Where Visual Basic has a ``for each'' statement to iterate over a
collection of items in a server, a WIN32OLE object has an each method (which takes a block) to accomplish the same
thing.
The following example, using Microsoft Excel,
illustrates most of
these concepts. First, we create a new WIN32OLE object attached
to Excel and set some cell values. Next we select
a range of cells and create a chart. We set the Type property in
the excelchart object to make it a 3D chart. Next we'll loop
through and change the chart rotation, 10° at a time. We'll add
a few charts, and we'll use each to step through and print them out.
Finally, we'll close down the Excel application and exit.
require 'win32ole'
# -4100 is the value for the Excel constant xl3DColumn.
ChartTypeVal = -4100;
# Creates OLE object to Excel
excel = WIN32OLE.new("excel.application")
# Create and rotate the chart
excel['Visible'] = TRUE;
workbook = excel.Workbooks.Add();
excel.Range("a1")['Value'] = 3;
excel.Range("a2")['Value'] = 2;
excel.Range("a3")['Value'] = 1;
excel.Range("a1:a3").Select();
excelchart = workbook.Charts.Add();
excelchart['Type'] = ChartTypeVal;
30.step(180, 10) do |rot|
excelchart['Rotation'] = rot
end
excelchart2 = workbook.Charts.Add();
excelchart3 = workbook.Charts.Add();
charts = workbook.Charts
charts.each { |i| puts i }
excel.ActiveWorkbook.Close(0);
excel.Quit();
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As with most (if not all) high-level languages, it can be all too easy
to churn out code that is unbearably slow, but that can be easily
fixed with a little thought.
With WIN32OLE, you need to be careful with unnecessary dynamic
lookups. Where possible, it is better to assign a WIN32OLE object
to a variable and then reference elements from it, rather than
creating a long chain of ``.'' expressions.
For example, instead of writing
workbook.Worksheets(1).Range("A1").value = 1
workbook.Worksheets(1).Range("A2").value = 2
workbook.Worksheets(1).Range("A3").value = 4
workbook.Worksheets(1).Range("A4").value = 8
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we can eliminate the common subexpressions by
saving the first part of the expression to a temporary
variable and then make calls from that variable:
worksheet = workbook.Worksheets(1)
worksheet.Range("A1").value = 1
worksheet.Range("A2").value = 2
worksheet.Range("A3").value = 4
worksheet.Range("A4").value = 8
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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 http://www.opencontent.org/openpub/)).
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.
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