System tray icon with Ruby and QT4 * ixti's personal scratchpad

System tray icon with Ruby and QT4

Date: 23 Jun 2010
Category: development/ruby
Tagged with: qt, ruby, and system-tray

In my previous post I have showed how to create a simple system tray icon in ruby and GTK. Today, I will create exactly the same application but with QT4 instead of GTK… Before I started this, I was full of optimism that it will be even easier to do this with QT. I was wrong :)) Because of some differences it was not as easy as I wish it to be…

I was going to start with similar simple and really dumb example. But some restrictions of QT disallowed me. So, to show a system tray icon, you need to call show instance method. But before this, you must set icon instance property, else it will throw a corresponding exception. So here’s most simple variant:

require 'Qt4'
app = Qt::Application.new(ARGV)
si  = Qt::SystemTrayIcon.new

si.icon = Qt::Icon.new('/path/to/some/image.png')
si.show

app.exec

There’s no stock images like in GTK, at least I didn’t found them, if you know - let me know. According to QT’s SDK there’s QIcon::fromTheme() static method, but unfortunately there’s no corresponding one in qt4ruby. So we can skip step with different types of icon image settings and go next. All snippets below will assume that there are app and si initializations before, and app.exec call after them. Now let’s make our icon start|stop blinking on left click.

In QT all clicks (left, middle, right, etc) are handled by one signal - activated(QSystemTrayIcon::ActivationReason). Not the easiest name of the signal to remember ;)) I spent about two hours trying to understand why SDK says that QStatusIcon has activated() signal, but my app tells me that there’s no such signal. Anyway, finally I got it. Here’s sample activated() signal handler:

si.connect(SIGNAL('activated(QSystemTrayIcon::ActivationReason)')) do |reason|
  case reason
    when Qt::SystemTrayIcon::Trigger:       puts 'Left Click'
    when Qt::SystemTrayIcon::MiddleClick:   puts 'Middle Click'
    when Qt::SystemTrayIcon::Context:       puts 'Right Click'
    when Qt::SystemTrayIcon::DoubleClick:   puts 'Double Click'
    else
  end
end

There’s also Qt::SystemTrayIcon::Unknown reason but this is not very useful IMHO. After we figured out how and where we need to handle left click, let’s make icon blinking. You probably will be surprised, but it’s not trivial as with GTK. Qt::SystemTrayIcon don’t have neither blinking instance property, nor any single method to make it blink. So to make icon blink we need to create a timer which will be replacing icon with empty one and restore original back again every 0.5 second:

# define standard icon, alternative (blank) one and current state handler
std_icon = Qt::Icon.new('/path/to/some/image.png')
alt_icon = Qt::Icon.new
blinking = false

# assign default icon
si.icon  = std_icon
si.show

# run timer to swap icons every 0.5 second if blinking is true
Qt::Timer.new(app) do |timer|
  timer.connect(SIGNAL('timeout()')) do
    si.icon = (si.icon.isNull ? std_icon : alt_icon) if blinking
  end
  timer.start(500)
end

# finally assign left click handler
si.connect(SIGNAL('activated(QSystemTrayIcon::ActivationReason)')) do |reason|
  if Qt::SystemTrayIcon::Trigger == reason
    blinking = !blinking
    si.icon  = blinking ? alt_icon : std_icon
  end
end

OK. It was not as easy as with GTK, but still, it works :)) So now let’s create context menu with exit item. First of all we need to create a Qt::Menu and populate it with Qt::Actions:

menu = Qt::Menu.new
quit = Qt::Action.new('&amp;Quit', menu)

quit.connect(SIGNAL(:triggered)) { app.quit }
menu.addAction(quit)

And now the most interesting part, as I told before QT’s system tray icon handles all clicks by one signal. But for context pop-up menu there’s a special instance property contextMenu exist. So to show a popup menu you need to assign it with menu so it will be popped up on right click! But remember, activated(QSystemTrayIcon::ActivationReason) will also be handled. So following code will pop up a menu and will output Right Click to the console:

si.contextMenu = menu

si.connect(SIGNAL('activated(QSystemTrayIcon::ActivationReason)')) do |reason|
  if Qt::SystemTrayIcon::Contex == treason
    puts 'Right Click'
  end
end

And now altogether again:

require 'Qt4'

app = Qt::Application.new(ARGV)
si  = Qt::SystemTrayIcon.new

std_icon = Qt::Icon.new('/path/to/some/image.png')
alt_icon = Qt::Icon.new
blinking = false

si.icon  = std_icon
si.show

Qt::Timer.new(app) do |timer|
  timer.connect(SIGNAL('timeout()')) do
    si.icon = (si.icon.isNull ? std_icon : alt_icon) if blinking
  end
  timer.start(500)
end

menu = Qt::Menu.new
quit = Qt::Action.new('&amp;Quit', menu)

quit.connect(SIGNAL(:triggered)) { app.quit }
menu.addAction(quit)

si.contextMenu = menu

si.connect(SIGNAL('activated(QSystemTrayIcon::ActivationReason)')) do |reason|
  case reason
    when Qt::SystemTrayIcon::Trigger
      blinking = !blinking
      si.icon  = blinking ? alt_icon : std_icon
    when Qt::SystemTrayIcon::MiddleClick:   puts 'Middle Click'
    when Qt::SystemTrayIcon::Context:       puts 'Right Click'
    when Qt::SystemTrayIcon::DoubleClick:   puts 'Double Click'
  end
end

app.exec

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