Layout management in PySide

Layout management in PySide

Important thing in GUI programming is the layout management. Layout management is the way how we place the widgets on the window. The management can be done in two ways. We can use absolute positioning or layout classes.

Absolute positioning

The programmer specifies the position and the size of each widget in pixels. When you use absolute positioning, you have to understand several things.

• the size and the position of a widget do not change, if you resize a window
• applications might look different on various platforms
• changing fonts in your application might spoil the layout
• if you decide to change your layout, you must completely redo your layout, which is tedious and time consuming

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PySide tutorial 

This example shows three labels on a window
using absolute positioning. 

author: Jan Bodnar
website: zetcode.com 
last edited: August 2011
"""

import sys
from PySide import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        label1 = QtGui.QLabel('Zetcode', self)
        label1.move(15, 10)

        label2 = QtGui.QLabel('tutorials', self)
        label2.move(35, 40)
        
        label3 = QtGui.QLabel('for programmers', self)
        label3.move(55, 70)        
        
        self.setGeometry(300, 300, 250, 150)
        self.setWindowTitle('Absolute')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

We simply call the move() method to position our widgets. In our case these widgets are labels. We position them by providing the x and the y coordinates. The beginning of the coordinate system is at the left top corner. The x values grow from left to right. The y values grow from top to bottom.

Figure: Absolute positioning

Box Layout

Layout management with layout classes is much more flexible and practical. It is the preferred way to place widgets on a window. The basic layout classes are QtGui.QHBoxLayout and QtGui.QVBoxLayout. They line up widgets horizontally and vertically.
Imagine that we wanted to place two buttons in the right bottom corner. To create such a layout, we will use one horizontal and one vertical box. To create the necessary space, we will add a stretch factor.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PySide tutorial 

In this example, we position two push
buttons in the bottom-right corner 
of the window. 

author: Jan Bodnar
website: zetcode.com 
last edited: August 2011
"""

import sys
from PySide import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        okButton = QtGui.QPushButton("OK")
        cancelButton = QtGui.QPushButton("Cancel")

        hbox = QtGui.QHBoxLayout()
        hbox.addStretch(1)
        hbox.addWidget(okButton)
        hbox.addWidget(cancelButton)

        vbox = QtGui.QVBoxLayout()
        vbox.addStretch(1)
        vbox.addLayout(hbox)
        
        self.setLayout(vbox)    
        
        self.setGeometry(300, 300, 300, 150)
        self.setWindowTitle('Buttons')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

The example places two buttons in the bottom-right corner of the window. They stay there when we resize the application window. We use both QtGui.HBoxLayout and QtGui.QVBoxLayout.

okButton = QtGui.QPushButton("OK")
cancelButton = QtGui.QPushButton("Cancel")

Here we create two push buttons.

hbox = QtGui.QHBoxLayout()
hbox.addStretch(1)
hbox.addWidget(okButton)
hbox.addWidget(cancelButton)

We create a horizontal box layout. Add a stretch factor and both buttons. The stretch adds a stretchable space before the two buttons. This will push them to the right of the window.

vbox = QtGui.QVBoxLayout()
vbox.addStretch(1)
vbox.addLayout(hbox)

To create the necessary layout, we put a horizontal layout into a vertical one. The stretch factor in the vertical box will push the horizontal box with the buttons to the bottom of the window.

self.setLayout(vbox)

Finally, we set the base layout of the window. It is the vertical box.

Figure: Buttons example

Grid layout

The most universal layout class in PySide is the grid layout. This layout divides the space into rows and columns. To create a grid layout, we use the QtGui.QGridLayout class.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PySide tutorial 

In this example, we create a skeleton
of a calculator using a QGridLayout.

author: Jan Bodnar
website: zetcode.com 
last edited: August 2011
"""

import sys
from PySide import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        names = ['Cls', 'Bck', '', 'Close', '7', '8', '9', '/',
                '4', '5', '6', '*', '1', '2', '3', '-',
                '0', '.', '=', '+']

        grid = QtGui.QGridLayout()

        j = 0
        pos = [(0, 0), (0, 1), (0, 2), (0, 3),
                (1, 0), (1, 1), (1, 2), (1, 3),
                (2, 0), (2, 1), (2, 2), (2, 3),
                (3, 0), (3, 1), (3, 2), (3, 3 ),
                (4, 0), (4, 1), (4, 2), (4, 3)]

        for i in names:
            button = QtGui.QPushButton(i)
            if j == 2:
                grid.addWidget(QtGui.QLabel(''), 0, 2)
            else: grid.addWidget(button, pos[j][0], pos[j][1])
            j = j + 1

        self.setLayout(grid)   
        
        self.move(300, 150)
        self.setWindowTitle('Calculator')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

In our example, we create a grid of buttons. To fill one gap, we also add one QtGui.QLabel widget.

grid = QtGui.QGridLayout()

Here we create a grid layout.

if j == 2:
    grid.addWidget(QtGui.QLabel(''), 0, 2)
else: grid.addWidget(button, pos[j][0], pos[j][1])

To add a widget to a grid, we call the addWidget() method. The arguments are the widget, the row and the column number.

Figure: Calculator skeleton

Review example

Widgets can span multiple columns or rows in a grid. In the next example we illustrate this.

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
ZetCode PySide tutorial 

In this example, we create a bit
more complicated window layout using
the QGridLayout manager. 

author: Jan Bodnar
website: zetcode.com 
last edited: August 2011
"""

import sys
from PySide import QtGui

class Example(QtGui.QWidget):
    
    def __init__(self):
        super(Example, self).__init__()
        
        self.initUI()
        
    def initUI(self):
        
        title = QtGui.QLabel('Title')
        author = QtGui.QLabel('Author')
        review = QtGui.QLabel('Review')

        titleEdit = QtGui.QLineEdit()
        authorEdit = QtGui.QLineEdit()
        reviewEdit = QtGui.QTextEdit()

        grid = QtGui.QGridLayout()
        grid.setSpacing(10)

        grid.addWidget(title, 1, 0)
        grid.addWidget(titleEdit, 1, 1)

        grid.addWidget(author, 2, 0)
        grid.addWidget(authorEdit, 2, 1)

        grid.addWidget(review, 3, 0)
        grid.addWidget(reviewEdit, 3, 1, 5, 1)
        
        self.setLayout(grid) 
        
        self.setGeometry(300, 300, 350, 300)
        self.setWindowTitle('Review')    
        self.show()
        
def main():
    
    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

We create a window in which we have three labels, two line edits and one text edit widget. The layout is done with the QtGui.QGridLayout.

grid = QtGui.QGridLayout()
grid.setSpacing(10)

We create a grid layout and set spacing between widgets.

grid.addWidget(reviewEdit, 3, 1, 5, 1)

If we add a widget to a grid, we can provide row span and column span of the widget. In our case, we make the reviewEdit widget span 5 rows.

Figure: Review example

This part of the PySide tutorial was dedicated to layout management.