Difference between revisions of "Development/Tutorials/Plasma4/Ruby/Using widgets"

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(Change module, and tell the reader to do this in de metadata.desktop file.)
m (Small fix in example code.)
Line 31: Line 31:
       label = Plasma::Label.new self
       label = Plasma::Label.new self
       label.text = "Hello world!"
       label.text = "Hello world!"
       self.layout.add_item label
       layout.add_item label
       self.layout = layout
       self.layout = layout

Revision as of 21:14, 25 January 2009

This is a 'translation' of the Using widgets article on Python and Plasma. For the Python Tutorial see here.


Using the paintInterface method to display applets is a powerful, and sometimes even necessary way of working. For example, when you want to display a SVG graphic. But it is not the only method available to create a Plasmoid, however. Plasma comes with a number of widgets "tailored" for use in Plasmoids. In this tutorial we will create a very simple "Hello, world!" Plasmoid using Plasma widgets.


Set up your applet directory and create a metadata.desktop file as described in the Getting Started tutorial. Don't forget to change the X-KDE-PluginInfo-Name line to match the module used in the tutorial (RubyWidget), otherwise the example will not work!

The 'main.rb' file

Here is how our main.rb file will look like:

  1. Copyright stuff

require 'plasma_applet'

module RubyWidget

 class Main < PlasmaScripting::Applet
   def initialize parent
     super parent
   def init
     self.has_configuration_interface = false
     self.aspect_ratio_mode = Plasma::Square
     self.background_hints = Plasma::Applet.DefaultBackground
     layout = Qt::GraphicsLinearLayout.new Qt::Horizontal, self
     label = Plasma::Label.new self
     label.text = "Hello world!"
     layout.add_item label
     self.layout = layout
     resize 125, 125


Let's take a deeper look at it. As in the main tutorial, we create our class by deriving from the PlasmaScripting::Applet class. In initialize, we quickly initialize the class. We use the init method instead to do all the dirty work of creating the applet and adding the widget needed to display the text.

First of all we tell Plasma that this applet does not have a configuration dialog (has_configuration_interface=). We then set the aspect ratio mode to a square (Plasma::Square). This is taken into account when someone resizes the applet. Next the background_hints= method sets the Plasmoid's background to the default Plasma background (Plasma::Applet.DefaultBackground) saving us from having to manually draw the background ourselves.

The third and most important step deals with creating a layout. It is a bit different than the standard Qt::LinearLayout seen in Qt, because it is done inside a Qt::GraphicsView used by Plasma. We want a simple, linear layout, and so we use a Qt::GraphicsLinearLayout, setting it to be horizontal (Qt::Horizontal).

Next we create a Plasma::Label. This is a widget that is Plasma aware and therefore uses all of the goodies provided by Plasma. For example, automatically changing its text color if the Plasma theme changes. We then use the text= method (analogous to the normal Qt::Label.text= method) to set our label text ("Hello, world!") and then add the label to the layout. Also, we set the applet's layout to be the one we have just defined using self.layout=. Finally we resize the applet to 125 x 125 pixels.

Once packaged and installed (see the Getting Started tutorial), the Plasmoid will look like this:



This brief tutorial shows how to use Plasma widgets with your applet. Beside Plasma::Label there are many more widgets that you can use.

Notice that at the moment you can only add widgets and create layouts directly in code. This means you can't use an application like Qt Designer to design the appearance of your applet.

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