[Closed] Checkbutton change state question- pressing checkbutton automatically?

Hi,
I have a question about running checkbutton,I want to run functions after changing the state of checkbutton，generally,we can do it like :

rollout only_test "" 
(
    checkbutton chk_test "Check Me!" 
    on chk_test changed state do 
    (
		print "Is changing state..."
    )
)
createDialog only_test 

So my question is ,how can I print “Is changing state…” without pressing the checkbutton but the codes can execute and checkbutton also change its state at the same time?
I tried this way,but only the state can change,no codes executed.

rollout only_test "" 
(
    checkbutton chk_test "Check Me!" 
    on chk_test changed state do 
    (
		print "Is changing state..."
	)
)
createDialog only_test 

only_test.chk_test.checked=true

or

rollout only_test "" 
(
    checkbutton chk_test "Check Me!" 
    on chk_test changed state do 
    (
		print "Is changing state..."
	)
)
createDialog only_test 

only_test.chk_test.checked=true
only_test.chk_test.checked=false

any suggestions?