Perl/TkFAQ-10.如何使用某个组件来完成某个工作
原文：
10. How do I get widget X to do Y ?
There are a number of tasks that can be accomplished with perl/Tk widgets, configurations, and bindings (a few that can't and a few that require specific tricks). Beginners are encouraged to work through the examples in UserGuide.pod. Some examples from UserGuide.pod are addressed in this document among those that follow.
Basically a widget can be "created" by simply calling the sub of the same name: my $main = new MainWindow;
will set aside the necessary system memory etc. for a new MainWindow widget (it does not appear until after the MainLoop; call). The object "created" is then callable via the variable $main. So, for example, if you wanted a Button in your MainWindow, then this: $main->Button();
would be a very basic example of a widget command. If you wanted to later call this button widget you would need a "widget tag or ID" to "get a handle on it". Instead of the above call try something like: my $button = $main->Button();
The variable $button is how you refer to the Button widget in subsequent calls, such as when we call the pack routine: $button -> pack;
A complete script that incorporates these ideas to make a very plain button would look like: #!/usr/bin/perl -w use Tk; use strict; my $main = new MainWindow; my $button = $main -> Button(); $button -> pack; MainLoop;
But who wants such a plain looking button? You can provide a number of different widget configurations via calls to the configure routine as in: #!/usr/bin/perl -w use Tk; use strict; my $main = new MainWindow; my $button = $main->Button(); $button -> configure(-text => 'Press me!'); $button -> pack; MainLoop;
The Perl motto is "there is more than one way to do it." - perl/Tk remains quite true to this motto as well. Note that the above script could have been written quite succinctly without the use of either the $main or $button variables as: #!/usr/bin/perl -w use Tk; use strict; new MainWindow -> Button(-text => 'Press me!') -> pack; MainLoop;
But if you want your widgets to actually do things then you must set up callback procedures as discussed later...
Do not overlook the - sign in front of some options (like -text in the above example) Another commonly overlooked problem is that elements in a hash are supposed to be strings hence a configuration option like -length +> 5, really ought to be specified as either '-length' +> 5, or "-length" +> 5, etc., rather than perl's builtin length() function.
译文：
10. 如何使用某个组件来完成某个工作？
通过使用Perl/Tk的各种组件，并进行必要的配置和绑定，可以实现很多功能。当然，也有少数的一些无法完成或需要一定的技巧才能完成。建议初学Tk的朋友仔细的学习和试用UserGuide.pod中的例程。在下面的讲解中，我们也会谈到其中的一些例子。
基本上，要创建一个组件，只需要调用和他名称对应的子程序，例如：
my $main = new MainWindow;
上面的语句将使Perl解释器为这个新的MainWindow组件留出一些必要的系统内存等资源（但是这个主窗口并非立刻出现的，它要直到调用 MainLoop才会出现）。这样，上面创建的这个对象，以后就可以通过变量$main来调用了。例如，如果你想在你的这个主窗口中放置一个按钮，就可以这样：
$main->Button();
那么，实现上面的几个想法的一般“完整”的脚本如下（这里将创建一个空白的按钮）：
#!/usr/bin/perl -w
use Tk;
use strict;
my $main = new MainWindow;
my $button = $main -> Button();
$button -> pack;
MainLoop;
但是谁会想要一个空白的按钮呢？其实，你可能通过使用configure方法对很多不同的组件进行配置。例如：
#!/usr/bin/perl -w
use Tk;
use strict;
my $main = new MainWindow;
my $button = $main->Button();
$button -> configure(-text => 'Press me!');
$button -> pack;
MainLoop;
众所周知，Perl的名言就是：做一件事情可以有多种方法。所以，Perl/Tk也同样信守了这一原则。其实，上面的脚本可以写的非常简洁，甚至不使用任何的变量（$main和$button），代码如下：
#!/usr/bin/perl -w
use Tk;
use strict;
new MainWindow -> Button(-text => 'Press me!') -> pack;
MainLoop;
当然，如果你确实希望你的组件实现一些功能的话，你还必须让它们关联一些代码，这我们将在以后详细讨论……
最后，我们提醒大家不要忽略了在选项前面的“－”符号，例如上面例子中的-text。另外，值得一提的是，hash中的元素默认被当作字符串看待，所以我们使用的配置选项如：-length => 5，事实上应该写成：’-length’ => 5或”-length” => 5，这样才可以和Perl的内置函数length()相区别。
