Create checkbox.rb

First commit for standalone checkbox.rb (checkbox widget).

examples2/checkbox.rb

@@ -0,0 +1,56 @@
+# ============================================================================ #
+# This example (checkbox.rb) shall demonstrate the following functionality
+# (5 components), as well as their implementation-status in regards to
+# this file:
+#
+#   :new_checkbox              # [DONE]
+#   :checkbox_checked          # [DONE]
+#   :checkbox_on_toggled       # [DONE]
+#   :checkbox_set_checked      # [DONE]
+#   :checkbox_set_text         # [DONE]
+#   :checkbox_text             # [DONE]
+#
+# ============================================================================ #
+require 'libui'
+LibUI.init # Initialize LibUI.
+
+main_window = LibUI.new_window('checkbox.rb', 400, 240, 1)
+
+hbox = LibUI.new_horizontal_box
+LibUI.box_set_padded(hbox, 1)
+
+_ = LibUI.new_checkbox # Create a new checkbox here.
+LibUI.box_append(hbox, _, 1) # Add it to a box.
+LibUI.checkbox_set_text(_, 'This is a generic text for the checkbox.')
+
+puts 'The text for our checkbox follows (obtained via LibUI.checkbox_text():'
+puts
+puts "  #{LibUI.checkbox_text(_)}"
+puts
+
+callback_for_the_checkbox = proc {
+  puts 'I was toggled. My state is now:'
+  case LibUI.checkbox_checked(_)
+  when 1
+    puts '  checked (active)'
+  when 0
+    puts '  unchecked (inactive)'
+  end
+  0 # This return value does not seem to be necessary, but we use it still, to show that one could use a return value here.
+}
+
+LibUI.checkbox_on_toggled(_, callback_for_the_checkbox)
+
+puts 'Setting the checkbox to checked (is-selected) next.'
+LibUI.checkbox_set_checked(_, 1)
+
+LibUI.window_set_child(main_window, hbox)
+LibUI.control_show(main_window)
+
+LibUI.window_on_closing(main_window) {
+  LibUI.quit
+  1
+}
+
+LibUI.main
+LibUI.uninit