User:Declan.mcgrath

Developing Ruby QT Applications using QT Designer and Ruby on Ubuntu

These instructions are tested with Ubuntu Jaunty Jackalope 9.04 . We will create a simple application to display a list of items (pieces of text) and move them up and down. Ground breaking in the extreme!

Install the appropriate packages

From a command line terminal run

• sudo aptitude install libkorundum4-ruby1.8
  
• sudo aptitude qt4-designer
  
• sudo aptitude libqt4-ruby1.8-dev
  
• sudo aptitude install libqt4-ruby1.8-examples
  
• sudo aptitude install qt4-doc qt4-doc-html  qt4-demos
  
• sudo aptitude install qt-creator (you may not need this)
  

Create a simple Form with QT4 Designer

• Create a folder on disk for your project, for example, my_first_project
• Start up QT4 Designer
  

1. Select QT 4 Designer from the Applications->Programming menu or...
   
2. From a command line terminal run: designer-qt4
   

• The default form is a Dialog with Buttons Right. Stick with that and click Create
  
• Drag a List View from the Item Widgets (Item-Based) selection of widgets on the left onto the form. Be careful NOT to choose the List View from the Item Widgets (Model-Based)
  
• Right-click the List View that is now dragged on the form
  

1. Select Edit Items
   
2. Click the green plus icon on the left to add an item
   
3. Enter the text: First line
   
4. Click the green plus icon on the left to add an item
5. Enter the text: Second line
6. Click OK to finish editing items

• In the Property Editor on the right, scroll down to the section QAbstractItemView
  
• Keep scrolling down a little more to the Property DragDropMode and change it's value to internal. This will let us move items up and down in the list easily
  
• Save what we've done by selecting Save As in the File Menu

1. Navigate to the folder you created earlier, my_first_project
   
2. Choose the filename dashboard.ui for your file and click save
3. This file contains and XML representation of the form you just created
   

• If you want to take a quick look at your form select Preview from the Form menu
  
• But we're done with GUI stuff now! Let's get hacking...

Creating the basic application structure

• Now that we've got a user interface, we need to run a command (rbuic4) that creates a Ruby class that we can use based on the interface
  
• From the command line terminal
  

1. Navigate to the my_first_project folder you created earlier using the cd command
   
2. Run the command 'rbuic4 dashboard.ui -x -o dashboard_ui.rb'
3. The '-o dashboard_ui.rb' bit of the command says dump the resulting ruby code into a file called dashboard_ui.rb
4. The '-x' bit of the command says to create a little stub (like a main function in C/C++ or public static void main in Java) that kicks off the application. Otherwise your application would have no entry point.
   
5. We need to rerun this command every time we change the form using QT4 Designer. Usually we won't add the '-x' flag
   
6. For instant gratification run the command 'ruby dashboard_ui.rb'
7. Woaa!!! You should see your beautiful form before you very eyes. But when the excitement dies down, be aware that if you were to add any code to your dashboard_ui.rb file it would get blown away every time we run rbuic4 on this file to pick up the latest changes we made to the UI using QT4 Designer. But it needn't be this way...
   

Separating generated code from our 'real' code

In QT4, this is achieved by subclassing the dashboard_ui.rb file. Using a text editor create a new file in your my_first_project folder called dashboard.rb. The comments should explain what's going on

1. We pull in the file containg the class containing the generated code

require 'dashboard_ui'

1. We inherit from the class containing the generated code.

class Dashboard < Ui::Dialog

   # We are then free to put our own code into this class without fear
   # of it being overwritten. Here we add a setup_ui function which
   # can be used to customise how the form looks on startup

   def setup_ui(dialog)
       super
       # We'll be putting some code here real soon...
   end

end

We now need to make see how we can control the look of the form using code

• Create a new file in the my_first_project folder called main.rb
• Move the following code from the dashboard_ui.rb file to main.rb
  

if $0 == __FILE__

   a = Qt::Application.new(ARGV)
   u = Ui_Dialog.new
   w = Qt::Dialog.new
   u.setupUi(w)
   w.show
   a.exec

end

Because we have our own main file now

• There is no need for the opening 'if $0 == __FILE__' line, so delete that line and it's enclosing 'end' statement
• We can move the inclusion of the Qt framework (require 'Qt') from the dashboard_ui.rb file to main.rb. Actually, we have to do this because in future we will run rbuic4 without the '-x' parameter; this would mean that the autogenerated code won't contain require 'Qt' so we'd run into problems
  
• We need to include our dashboard.rb file containing the 'real' code at the top the file

1. This is done using 'require 'dashboard'
2. You may have guessed by now that you don't need to add the '.rb' extension when including a ruby file. The Ruby interpreter is clever enough to figure out that it should look for a .rb file

• We can change the line 'u = Ui_Dialog.new' to 'u = Ui::Dialog.new'

1. The latter is more Rubyesque. If you look in the autogenerated file dashboard_ui.rb, you will see that there is done using a module definition near the end. This is just syntatic sugar for Rubyists
2. Similarly, you can see in the same file that the funtion sampleUi() is wrapped by another function sample_ui()
3. Again, this is just aesthetics. Syntactic sugar, but important syntactic sugar nonetheless!
   

• This gives us

require 'Qt' require 'dashboard' a = Qt::Application.new(ARGV) u = Ui_Dialog.new w = Qt::Dialog.new u.setupUi(w) w.show a.exec