Cheat Engine

[Freiza]

[Dark Byte]

I'm assuming you're trying to use the checkbox of a Cheat component that the automated trainer generator creates for you.

In that case, check this:
http://forum.cheatengine.org/viewtopic.php?t=537515

Once you get the checkbox you can use checkbox_ specific functions on it, like checkbox_onChange(cb, CheckboxStateChangefunction)

note that the checkbox of a "Cheat" component is linked to the Active property so watch for infinite loops

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alternatively, instead of making use of the old generic ce 5.x CheatList object create your own gui instead with a checkbox that you place and control yourself