Development/Tutorials/Qt4 Ruby Tutorial/Chapter 06

    From KDE TechBase
    Revision as of 17:40, 2 July 2011 by Aspotashev (talk | contribs) (add link to chapter 5)
    Other languages:


    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 Galore!

    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()
    
    app.exec()
    

    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.