PL/I 语言图形界面（GUI）元素创建与布局实战
PL/I（Programming Language One）是一种高级程序设计语言，它结合了多种编程语言的特性，旨在提高编程效率和代码的可读性。尽管PL/I在现代编程中不如C、C++或Java等语言流行，但在某些领域，如大型系统编程和科学计算，它仍然有其独特的应用。本文将探讨如何使用PL/I语言创建图形界面（GUI）元素，并进行布局实战。
环境准备
在开始之前，我们需要准备一个PL/I编译器和支持GUI开发的库。以下是一个简单的环境配置步骤：
1. 安装PL/I编译器，如IBM PL/I for z/OS。
2. 选择一个支持GUI开发的库，如Openmotif或Motif。
GUI库简介
在PL/I中，我们可以使用Motif库来创建GUI应用程序。Motif是一个开放源代码的GUI工具包，它提供了丰富的控件和布局管理器。
控件
Motif提供了以下常用控件：
- Button：按钮
- Label：标签
- Text：文本框
- List：列表框
- Menu：菜单
- Dialog：对话框
布局管理器
Motif提供了以下布局管理器：
- Form：表单布局
- Grid：网格布局
- Pack：包装布局
创建GUI应用程序
以下是一个简单的PL/I程序，它创建了一个包含按钮和标签的窗口。
pl/i
identification division.
program-id. create-gui.
environment division.
input-output section.
file-control.
select standard-output assign to stdout.
select standard-error assign to stderr.
data division.
file section.
working-storage section.
01 window-id pic x(32).
01 button-id pic x(32).
01 label-id pic x(32).
procedure division.
display "Creating GUI window..."
call "XtOpenDisplay" using by value "localhost:0" by reference window-id
by value "MyApp" by value "Motif" by value 0
by reference 0 by value 0.
if window-id = 0 then
display "Failed to open display."
stop run.
end-if.
call "XtCreateWindow" using by value window-id by value "topLevel" by reference window-id
by value "ApplicationShell" by value 0 by value 0 by value 0.
call "XtCreateButton" using by value window-id by reference button-id
by value "Button" by value "XtCreateButton" by value 0 by value 0 by value 0.
call "XtCreateLabel" using by value window-id by reference label-id
by value "Hello, World!" by value "XtCreateLabel" by value 0 by value 0 by value 0.
call "XtRealizeWidget" using by value window-id.
call "XtMainLoop" using by value window-id.
end program create-gui.
布局实战
在上面的程序中，我们创建了一个包含按钮和标签的窗口。现在，我们将学习如何使用Motif的布局管理器来调整这些元素的位置和大小。
使用Form布局
Form布局是一种将控件组织成行和列的布局方式。以下代码演示了如何使用Form布局管理器：
pl/i
call "XtCreateWidget" using by value window-id by reference form-id
by value "form" by value "Form" by value 0 by value 0 by value 0.
call "XtCreateWidget" using by value form-id by reference button-id
by value "Button" by value "Button" by value 0 by value 0 by value 0.
call "XtCreateWidget" using by value form-id by reference label-id
by value "Label" by value "Label" by value 0 by value 0 by value 0.
call "XtManageChild" using by value form-id by value button-id.
call "XtManageChild" using by value form-id by value label-id.
使用Grid布局
Grid布局是一种将控件组织成网格的布局方式。以下代码演示了如何使用Grid布局管理器：
pl/i
call "XtCreateWidget" using by value window-id by reference grid-id
by value "grid" by value "Grid" by value 0 by value 0 by value 0.
call "XtCreateWidget" using by value grid-id by reference button-id
by value "Button" by value "Button" by value 0 by value 0 by value 0.
call "XtCreateWidget" using by value grid-id by reference label-id
by value "Label" by value "Label" by value 0 by value 0 by value 0.
call "XtManageChild" using by value grid-id by value button-id.
call "XtManageChild" using by value grid-id by value label-id.
使用Pack布局
Pack布局是一种将控件垂直或水平排列的布局方式。以下代码演示了如何使用Pack布局管理器：
pl/i
call "XtCreateWidget" using by value window-id by reference pack-id
by value "pack" by value "Pack" by value 0 by value 0 by value 0.
call "XtCreateWidget" using by value pack-id by reference button-id
by value "Button" by value "Button" by value 0 by value 0 by value 0.
call "XtCreateWidget" using by value pack-id by reference label-id
by value "Label" by value "Label" by value 0 by value 0 by value 0.
call "XtManageChild" using by value pack-id by value button-id.
call "XtManageChild" using by value pack-id by value label-id.
总结
本文介绍了如何使用PL/I语言和Motif库创建图形界面应用程序。我们学习了如何创建基本的GUI元素，并使用不同的布局管理器来调整它们的位置和大小。尽管PL/I在现代编程中不如其他语言流行，但了解如何使用它来创建GUI应用程序仍然是一个有价值的技能。
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