Layout management
In this part of the Ruby Qt programming tutorial, we will introduce layout managers.
When we design the GUI of our application, we decide what components we will use and how we will organize those components in the application. To organize our components, we use specialized non visible objects called layout managers. There are several options in Qt. We can use absolute positioning, built-in layout managers or create a custom layout manager. We can also visually build the layouts using the Qt Designer.
Qt has some important built-in layout managers. The VBoxLayout class lines up widgets vertically. HBoxLayout lines up widgets horizontally. The GridLayout class lays out widgets in a grid. The grid layout is the most flexible layout manager. The box layouts nest into one another to create complex layouts.
Absolute positioning
In most cases, programmers should use layout managers. There are a few situations, where we can use absolute positioning. In absolute positioning, the programmer specifies the position and the size of each widget in pixels. The size and the position of a widget do not change, if you resize a window. Applications look different on various platforms, and what looks OK on Linux, might not look OK on Mac. Changing fonts in your application might spoil the layout. If you translate your application into another language, you must redo your layout. For all these issues, use the absolute positioning only when you have a reason to do so.
#!/usr/bin/ruby
# ZetCode Ruby Qt tutorial
#
# In this program, we lay out widgets
# using absolute positioning
#
# author: jan bodnar
# website: www.zetcode.com
# last modified: June 2009
require 'Qt'
class QtApp < Qt::Widget
def initialize
super
setWindowTitle "Absolute"
init_ui
resize 300, 280
move 300, 300
show
end
def init_ui
setStyleSheet "QWidget { background-color: #414141 }"
bardejov = Qt::Pixmap.new "bardejov.jpg"
rotunda = Qt::Pixmap.new "rotunda.jpg"
mincol = Qt::Pixmap.new "mincol.jpg"
barLabel = Qt::Label.new self
barLabel.setPixmap bardejov
barLabel.move 20, 20
rotLabel = Qt::Label.new self
rotLabel.setPixmap rotunda
rotLabel.move 40, 160
minLabel = Qt::Label.new self
minLabel.setPixmap mincol
minLabel.move 170, 50
end
end
app = Qt::Application.new ARGV
QtApp.new
app.exec
In this example, we show three images using the absolute positioning.
barLabel = Qt::Label.new self barLabel.setPixmap bardejov
The Label widget is used to hold the image.
barLabel.move 20, 20
We use the move method to position the label on the window at x=20, y=20.
When we resize the window, the labels retain their initial size.
Buttons example
In the following example, we will position two buttons in the bottom right corner of the window.
#!/usr/bin/ruby
# ZetCode Ruby Qt tutorial
#
# In this program, use box layouts
# to position two buttons in the
# bottom right corner of the window
#
# author: jan bodnar
# website: www.zetcode.com
# last modified: June 2009
require 'Qt'
class QtApp < Qt::Widget
def initialize
super
setWindowTitle "Buttons"
init_ui
resize 330, 170
move 300, 300
show
end
def init_ui
vbox = Qt::VBoxLayout.new self
hbox = Qt::HBoxLayout.new
ok = Qt::PushButton.new "OK", self
apply = Qt::PushButton.new "Apply", self
hbox.addWidget ok, 1, Qt::AlignRight
hbox.addWidget apply
vbox.addStretch 1
vbox.addLayout hbox
end
end
app = Qt::Application.new ARGV
QtApp.new
app.exec
We use nested box layouts to get our intended layout.
vbox = Qt::VBoxLayout.new self hbox = Qt::HBoxLayout.new
We use one vertical and one horizontal box.
ok = Qt::PushButton.new "OK", self apply = Qt::PushButton.new "Apply", self
These are the two buttons, that will go into the bottom right corner of the window.
hbox.addWidget ok, 1, Qt::AlignRight
We put the ok button into the horizontal box. The second parameter is the stretch factor. It expands the area allotted to the ok button. It takes all available space left. Inside this area, the button is aligned to the right.
vbox.addStretch 1
This line creates a vertically expanded white space, which will push the horizontal box with the buttons to the bottom.
vbox.addLayout hbox
The horizontal box is nested into the vertical box.
Windows example
The following is a more complicated example with nested box layouts.
#!/usr/bin/ruby
# ZetCode Ruby Qt tutorial
#
# In this program, use box layouts
# to create a Windows example
#
# author: jan bodnar
# website: www.zetcode.com
# last modified: June 2009
require 'Qt'
class QtApp < Qt::Widget
def initialize
super
setWindowTitle "Windows"
init_ui
resize 350, 300
move 300, 300
show
end
def init_ui
vbox = Qt::VBoxLayout.new self
vbox1 = Qt::VBoxLayout.new
hbox1 = Qt::HBoxLayout.new
hbox2 = Qt::HBoxLayout.new
windLabel = Qt::Label.new "Windows", self
edit = Qt::TextEdit.new self
edit.setEnabled false
activate = Qt::PushButton.new "Activate", self
close = Qt::PushButton.new "Close", self
help = Qt::PushButton.new "Help", self
ok = Qt::PushButton.new "OK", self
vbox.addWidget windLabel
vbox1.addWidget activate
vbox1.addWidget close, 0, Qt::AlignTop
hbox1.addWidget edit
hbox1.addLayout vbox1
vbox.addLayout hbox1
hbox2.addWidget help
hbox2.addStretch 1
hbox2.addWidget ok
vbox.addLayout hbox2, 1
setLayout vbox
end
end
app = Qt::Application.new ARGV
QtApp.new
app.exec
In this layout, we use two vertical and horizontal boxes.
box = Qt::VBoxLayout.new self
This is the base layout of the example.
windLabel = Qt::Label.new "Windows", self
First goes the label widget. It goes simply to the top of the vertical box.
vbox1.addWidget activate vbox1.addWidget close, 0, Qt::AlignTop hbox1.addWidget edit hbox1.addLayout vbox1 vbox.addLayout hbox1
In the center part of the window we have a text edit widget and two vertically lined up buttons. The buttons go into a vertical box. The buttons are aligned to the top within this vertical box. The vertical box and the text edit go into a horizontal box. This horizontal box goes to the base vertical box, just below the label widget.
hbox2.addWidget help hbox2.addStretch 1 hbox2.addWidget ok vbox.addLayout hbox2, 1
The help and the ok button go into another horizontal box. There is an expanded white space between these two buttons. Again, the horizontal box goes to the base vertical box.
setLayout vbox
The base vertical box is set to be the main layout of the window.
New Folder example
In the last example, we use the GridLayout manager to create a New Folder layout example.
#!/usr/bin/ruby
# ZetCode Ruby Qt tutorial
#
# In this program, use the GridLayout
# to create a New Folder example
#
# author: jan bodnar
# website: www.zetcode.com
# last modified: June 2009
require 'Qt'
class QtApp < Qt::Widget
def initialize
super
setWindowTitle "New Folder"
init_ui
resize 300, 300
move 300, 300
show
end
def init_ui
grid = Qt::GridLayout.new self
nameLabel = Qt::Label.new "Name", self
nameEdit = Qt::LineEdit.new self
text = Qt::TextEdit.new self
okButton = Qt::PushButton.new "OK", self
closeButton = Qt::PushButton.new "Close", self
grid.addWidget nameLabel, 0, 0
grid.addWidget nameEdit, 0, 1, 1, 3
grid.addWidget text, 1, 0, 2, 4
grid.setColumnStretch 1, 1
grid.addWidget okButton, 4, 2
grid.addWidget closeButton, 4, 3
end
end
app = Qt::Application.new(ARGV)
QtApp.new
app.exec
In our example, we have one label, one line edit, one text edit and two buttons.
grid = Qt::GridLayout.new self
We create an instance of the GridLayout manager.
grid.addWidget nameLabel, 0, 0
We place the label widget in the first cell of the grid. The cells count from 0. The last two parameters are the row and column number.
grid.addWidget nameEdit, 0, 1, 1, 3
The line edit widget is placed at the first row, second column. The last two parameters are the row span and the column span. Horizontally, the widget will span three columns.
grid.setColumnStretch 1, 1
The parameters of the method are the column number and the stretch factor. Here we set stretch factor 1 to the second column. This means, that this column will take all remaining space. This was set, because we wanted our buttons to retain their initial size.
In this part of the Ruby Qt tutorial, we mentioned layout management of widgets.