Multiplatform Programming Guide/ja

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日本語版メニュー
メインページ - Lazarus Documentation日本語版 - 翻訳ノート - 日本語障害情報

このページは、マルチプラットホーム アプリケーションを書くにあたって考慮すべきチュートリアルの最初のページです。ここでは、これから移植をおこないやすいようなプログラムを書くために、必要な注意事項と、すでに製作したプログラムの移植のプロセスをのべています。この記事をよりよいものにするために、手助けしてくれる他の人を募集しています。

マルチプラットフォームプログラミングへの招待

どれくらい沢山の種類のパソコンが必要になるでしょう?

To answer this question, you should first determine who your potential users are and how your program will be used. This question depends on where you are deploying your application.

For example, on Europe, if you're developing desktop software you may decide that it only makes sense to develop for Windows and OS X. OS X is the most popular Unix in the world and is surging on the desktop, whereas Linux has mostly stalled there. Remember the 100:10:1 rule, which says that in any large organization or group of users, it's not unusual to find Windows, Mac and Linux desktop computers in roughly these ratios.

On other places, like South America, Windows is mostly dominant, Linux is rising as a desktop platform, even outselling Windows on big supermarket networks, and Mac OS X is restricted to Video and Sound work.

Are the handful of users running OS X and Linux worth the extra effort that will be required to develop, package, distribute and support separate versions for them? Obviously if the project requires this, then the answer will be yes. Or if the amount of extra effort will be small, then the answer will probably be yes as well. If you want to support them out of principle, then the answer may also be yes as long as the extra effort doesn't get in the way of finishing the software.

If you're developing software that will run on a Web server, the most used platform by far is UNIX, on all flavors. In this case, perhaps only Linux, Solaris, *BSD and other Unixes make sense as your target platforms. You may also want to add support for Windows NT.

もし、ひとつのプラットフォームについて開発をおこなうならば、(そして、将来にわたって他のプラットフォームをサポートしないならば)おそらくFreePascalとLazarusは仕事には最適なツールではないかもしれません。 もし、Windowsのデスクトップのソフトウエアのみを書くならば、Delphiのようがよりよい選択かもしれません。

一度、クロスプラットフォーム開発をマスターすれば、通常は、ソフトウエアの設計や、問題解決にのみ、注力すればよく、どんなプラットフォームで動作させるかについては、ほとんど楽観的に、自由に考えていれば良いことになります。 つまり、1つのプラットフォームで書いている時と同様、クロスプラットフォーム開発を身に付けていれば、他のプラットフォームについての特有な問題はほとんど無視すればいいのです。 しかしながら、いくつかの点で、異なるプラットフォームでプログラムをテストしたり、実際に走らせることは、すべてのターゲットのOSで適用できているかどうか判断する助けになるでしょう。

もし、異なる物理的なPCがいやだったら、デュアルブートのWindows-LinuxのPCや、Mac上の仮想マシンの下で動くWindowsやLinuxを使うとよいでしょう。

Windows と Linux間での相互移植

Windows API 関数

多くのWindowsプログラムは、WindowsAPIを使っています。クロスプラットホームアプリケーションでは、それらのコードは現れないか、({$IFDEF Win32}のような)コンパイル条件中に隠されるべきです。

幸いにもよく使われる多くのWindowsAPI関数はマルチプラットホーム流にLCLIntfに隠蔽され実装されています。これは、本当にWindowsAPIに多くを依存するプログラムにとって、解決策となるものです。 クロスプラットホームコンポーネントであるLCLを使って置き換えるのがベストです。 たとえば、GDI描画関数は、TCanvasのメンバ関数に置き換えられます。

ファイルシステムの違い

A basic concern when porting application between Linux and Windows is the file system. To start with Windows filenames are not case sensitive, while they are on Unix platforms. This can be the cause of annoying bugs, so any portable application should use consistently filenames.

リナックスでは "application directory" はありません

One concern when porting applications between Linux and Windows is the file system. Many programmers are used to call ExtractFilePath(ParamStr(0)) or Application.ExeName to get the location of the executable, and then search for the necessary files for the program execution (Images, XML files, database files, etc) based on the location of the executable. This is incorrect in Linux. The string on ParamStr(0) may not only not contain the directory of the executable, as it also varies between different shell programs (sh, bash, etc).

Even if Application.ExeName could in fact know the directory where the file under execution is, that file could be a symbolic link, so you would get the directory of the link instead.

So what should we do? On Linux you should use two different places to store configurations and resource files:

  • Resource files (i.e. images, help files)

A fixed privileged location for the executable and resource files which will not change.

This location can be something like: /usr/share/app_name or /opt/app_name

Most programs will be executed without root privileges and the fixed directory for a given application usually only available for the root user to write, so don't write on this directory. Only read information from it.

  • Configuration files

You can use the GetAppConfigDir function from SysUtils unit to get a suitable place to store configuration files on different system. The function has one parameter, called Global. If it is True then the directory returned is a global directory, i.e. valid for all users on the system. If the parameter Global is false, then the directory is specific for the user who is executing the program. On systems that do not support multi-user environments, these two directories may be the same.

There is also the GetAppConfigFile witch will return an appropriate name for an application configuration file.

Here is an example of the output of those functions on different systems:

program project1;

{$mode objfpc}{$H+}

uses
  SysUtils;

begin
  WriteLn(GetAppConfigDir(True));
  WriteLn(GetAppConfigDir(False));
  WriteLn(GetAppConfigFile(True));
  WriteLn(GetAppConfigFile(False));
end.

The output on a GNU/Linux system:

/etc
/home/felipe/project1
/etc/project1.cfg
/home/felipe/.project1

You can notice that glocal configuration files are stored on the /etc directory and local configurations are stored on a hidden folder on the user's home directory. Directories whose name begin with a dot (.) are hidden on Linux. You can create a directory on the location returned by GetAppConfigDir and then store configuration files there.

The output on Windows XP:

C:\Programas\teste
C:\Documents and Settings\felipe\Configurações Locais\Dados de aplicativos\project2
C:\Programas\teste\project2.cfg
C:\Documents and Settings\felipe\Configurações Locais\Dados de aplicativos\project2\project2.cfg

Notice that the function uses the directory where the application is to store global configurations on Windows.

Note: The use of UPX interferes with the use of the GetAppConfigDir and GetAppConfigFile functions.

WindowsのCOMオートメーションなしで、それをやる

With Windows, Automation is a powerful way not only of manipulating other programs remotely but also for allowing other programs to manipulate your program. With Delphi you can make your program both an Automation client and an Automation server, meaning it can both manipulate other programs and in turn be manipulated by other programs.

Unfortunately, Automation isn't available on OS X and Linux. However, you can simulate some of the functionality of Automation on OS X using AppleScript.

AppleScript is similar to Automation in some ways. For example, you can write scripts that manipulate other programs. Here's a very simple example of AppleScript that starts NeoOffice (the Mac version of OpenOffice.org):

 tell application "NeoOffice"
   launch
 end tell

An app that is designed to be manipulated by AppleScript provides a "dictionary" of classes and commands that can be used with the app, similar to the classes of a Windows Automation server. However, even apps like NeoOffice that don't provide a dictionary will still respond to the commands "launch", "activate" and "quit". AppleScript can be run from the OS X Script Editor or Finder or even converted to an app that you can drop on the dock just like any app. You can also run AppleScript from your program, as in this example:

 Shell('myscript.applescript');

This assumes the script is in the indicated file. You can also run scripts on the fly from your app using the OS X OsaScript command:

 Shell('osascript -e '#39'tell application "NeoOffice"'#39 +
       ' -e '#39'launch'#39' -e '#39'end tell'#39);
       {Note use of #39 to single-quote the parameters}

However, these examples are just the equivalent of the following Open command:

 Shell('open -a NeoOffice');

The real power of AppleScript is to manipulate programs remotely to create and open documents and automate other activities. How much you can do with a program depends on how extensive its AppleScript dictionary is (if it has one). For example, Microsoft's Office X programs are not very useable with AppleScript, whereas the newer Office 2004 programs have completely rewritten AppleScript dictionaries that compare in many ways with what's available via the Windows Office Automation servers.

While Linux shells support sophisticated command line scripting, the type of scripting is limited to what can be passed to a program on the command line. No access to a program's internal classes and commands are available with Linux the way they are via Windows Automation and OS X AppleScript.

As with Windows, many OS X and Linux programs are made up of multiple library files (.dylib and .so extensions). Sometimes these libraries are designed so you can also use them in programs you write. While this can be a way of adding some of the functionality of an external program to your program, it's not really the same as running and manipulating the external program itself. Instead, your program is just linking to and using the external program's library similar to the way it would use any programming library.

付記