Fix for cases where the receiver cannot be the owner of the callback

Fix #33
* uiTimer
* uiQueueMain
* uiOnShouldQuit

examples/draw_text.rb

@@ -124,10 +124,9 @@ def draw_event(adp, attr_str, font_button, alignment)
 handler.DragBroken   = do_nothing
 handler.KeyEvent     = key_event
 
-should_quit = proc do
+UI.on_should_quit do
   UI.control_destroy(main_window)
 end
-UI.on_should_quit(should_quit)
 
 @attr_str = make_attribute_string
 

examples/spectrum.rb

@@ -99,14 +99,12 @@ def spec
   0
 end
 UI.control_show(main_window)
-# FIXME
-redraw = Fiddle::Closure::BlockCaller.new(4, [0]) do
-  UI.area_queue_redraw_all(area)
-  1
-end
-timer = proc do
-  UI.timer(100, redraw)
+
+UI.queue_main do
+  UI.timer(100) do
+    UI.area_queue_redraw_all(area)
+    1
+  end
 end
-UI.queue_main(&timer)
 UI.main
 UI.quit

lib/libui/libui_base.rb

@@ -12,24 +12,29 @@ module LibUIBase
 
         # The proc object is converted to a Closure::BlockCaller object.
         args.map!.with_index do |arg, idx|
-          if arg.is_a?(Proc)
-            # The types of the function arguments are recorded beforehand.
-            # See the monkey patch in ffi.rb.
-            callback = Fiddle::Closure::BlockCaller.new(
-              *func.callback_argument_types[idx][1..2], &arg
-            )
-            # Protect from GC
-            # See https://github.com/kojix2/LibUI/issues/8
-            receiver = args[0]
-            if receiver.instance_variable_defined?(:@callbacks)
-              receiver.instance_variable_get(:@callbacks) << callback
-            else
-              receiver.instance_variable_set(:@callbacks, [callback])
-            end
-            callback
+          next arg unless arg.is_a?(Proc)
+
+          # now arg must be Proc
+
+          # The types of the function arguments are recorded beforehand.
+          # See the monkey patch in ffi.rb.
+          callback = Fiddle::Closure::BlockCaller.new(
+            *func.callback_argument_types[idx][1..2], &arg
+          )
+          # Protect from GC
+          # by giving the owner object a reference to the callback.
+          # See https://github.com/kojix2/LibUI/issues/8
+          owner = if (idx == 0 or owner.frozen?) #  e.g. UI.queue_main{}; UI.timer(100) {}
+                    LibUIBase # or UI is better?
+                  else
+                    args[0] # receiver
+                  end
+          if owner.instance_variable_defined?(:@callbacks)
+            owner.instance_variable_get(:@callbacks) << callback
           else
-            arg
+            owner.instance_variable_set(:@callbacks, [callback])
           end
+          callback
         end
 
         # Make it possible to omit the last nil. This may be an over-optimization.