Difference between revisions of "Development/Tutorials/Qt4 Ruby Tutorial/Chapter 06"

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=== Line by Line Walkthrough ===
 
=== Line by Line Walkthrough ===
 +
<code ruby>
 +
class LCDRange < Qt::Widget
 +
</code>
 +
 +
The LCDRange widget is a widget without any API. It just has a constructor. This sort of widget is not very useful, so we'll add some API later.
 +
 +
<code ruby>
 +
def initialize(parent = nil)
 +
    super()
 +
    lcd = Qt::LCDNumber.new(2)
 +
    slider = Qt::Slider.new(Qt::Horizontal)
 +
    slider.setRange(0, 99)
 +
    slider.setValue(0)
 +
 +
    connect(slider, SIGNAL('valueChanged(int)'), lcd, SLOT('display(int)'))
 +
 +
    layout = Qt::VBoxLayout.new()
 +
    layout.addWidget(lcd)
 +
    layout.addWidget(slider)
 +
    setLayout(layout)
 +
end
 +
</code>
 +
 +
This is lifted straight from the MyWidget constructor in Chapter 5. The only differences are that the Quit button is left out and the class is renamed.
 +
 +
<code ruby>
 +
class MyWidget < Qt::Widget
 +
</code>
 +
 +
MyWidget, too, contains no API except a constructor.
 +
 +
<code ruby>
 +
  def initialize(parent = nil)
 +
    super()
 +
    quit = Qt::PushButton.new(tr('Quit'))
 +
    quit.setFont(Qt::Font.new('Times', 18, Qt::Font::Bold))
 +
    connect(quit, SIGNAL('clicked()'), $qApp, SLOT('quit()'))
 +
</code>
 +
 +
The push button that used to be in what is now LCDRange has been separated so that we can have one Quit button and many LCDRange objects.
 +
 +
<code ruby>
 +
    grid = Qt::GridLayout.new()
 +
</code>
 +
 +
We create a Qt::Widget with a Qt::GridLayout that will contain three columns. The Qt::GridLayout automatically arranges its widgets in rows and columns; you can specify the row and column numbers when adding widgets to the layout, and Qt::GridLayout will fit them into the grid.
 +
 +
<code ruby>
 +
for row in 0..2
 +
      for column in 0..2
 +
        grid.addWidget(LCDRange.new(), row, column)
 +
      end
 +
end
 +
</code>
 +
 +
We create nine LCDRange widgets, all of which are children of the grid object, and we arrange them in three rows and three columns.
 +
 +
=== Running the Application ===
 +
This program shows how easy it is to use many widgets at a time. Each one behaves like the slider and LCD number in the previous chapter. Again, the difference lies in the implementation.
 +
 +
=== Exercises ===
 +
Initialize each slider with a different/random value on startup.

Revision as of 06:14, 30 December 2009


Contents

Development/Tutorials/Qt4 Ruby Tutorial/Chapter 06


Building Blocks Galore!
Tutorial Series   Qt4 Ruby Tutorial
Previous   Tutorial 5 - Building Blocks
What's Next   Tutorial 7 - One Thing Leads to Another
Further Reading   n/a

Building Blocks

Qt4 Ruby Tutorial Screenshot 6.png

Files:

Overview

This example shows how to encapsulate two widgets into a new component and how easy it is to use many widgets. For the first time, we use a custom widget as a child widget.

require 'Qt4'

class LCDRange < Qt::Widget

 def initialize(parent = nil)
   super()
   lcd = Qt::LCDNumber.new(2)
   slider = Qt::Slider.new(Qt::Horizontal)
   slider.setRange(0, 99)
   slider.setValue(0)
   connect(slider, SIGNAL('valueChanged(int)'), lcd, SLOT('display(int)'))
   layout = Qt::VBoxLayout.new()
   layout.addWidget(lcd)
   layout.addWidget(slider)
   setLayout(layout)
 end

end

class MyWidget < Qt::Widget

 def initialize(parent = nil)
   super()
   quit = Qt::PushButton.new(tr('Quit'))
   quit.setFont(Qt::Font.new('Times', 18, Qt::Font::Bold))
   connect(quit, SIGNAL('clicked()'), $qApp, SLOT('quit()'))
   grid = Qt::GridLayout.new()
   
   for row in 0..2
     for column in 0..2
       grid.addWidget(LCDRange.new(), row, column)
     end
   end
   layout = Qt::VBoxLayout.new()
   layout.addWidget(quit)
   layout.addLayout(grid)
   setLayout(layout)
 end

end

app = Qt::Application.new(ARGV)

widget = MyWidget.new() widget.show()

Line by Line Walkthrough

class LCDRange < Qt::Widget

The LCDRange widget is a widget without any API. It just has a constructor. This sort of widget is not very useful, so we'll add some API later.

def initialize(parent = nil)

   super()
   lcd = Qt::LCDNumber.new(2)
   slider = Qt::Slider.new(Qt::Horizontal)
   slider.setRange(0, 99)
   slider.setValue(0)
   connect(slider, SIGNAL('valueChanged(int)'), lcd, SLOT('display(int)'))
   layout = Qt::VBoxLayout.new()
   layout.addWidget(lcd)
   layout.addWidget(slider)
   setLayout(layout)

end

This is lifted straight from the MyWidget constructor in Chapter 5. The only differences are that the Quit button is left out and the class is renamed.

class MyWidget < Qt::Widget

MyWidget, too, contains no API except a constructor.

 def initialize(parent = nil)
   super()
   quit = Qt::PushButton.new(tr('Quit'))
   quit.setFont(Qt::Font.new('Times', 18, Qt::Font::Bold))
   connect(quit, SIGNAL('clicked()'), $qApp, SLOT('quit()'))

The push button that used to be in what is now LCDRange has been separated so that we can have one Quit button and many LCDRange objects.

   grid = Qt::GridLayout.new()

We create a Qt::Widget with a Qt::GridLayout that will contain three columns. The Qt::GridLayout automatically arranges its widgets in rows and columns; you can specify the row and column numbers when adding widgets to the layout, and Qt::GridLayout will fit them into the grid.

for row in 0..2

     for column in 0..2
       grid.addWidget(LCDRange.new(), row, column)
     end

end

We create nine LCDRange widgets, all of which are children of the grid object, and we arrange them in three rows and three columns.

Running the Application

This program shows how easy it is to use many widgets at a time. Each one behaves like the slider and LCD number in the previous chapter. Again, the difference lies in the implementation.

Exercises

Initialize each slider with a different/random value on startup.

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