iphone - How to trigger UIControlEventTouchCancel? -

i thought uicontroleventtouchcancel triggered when tap on button , drag out of it. i'm doing , event handler never called.

i have class inherits uicontrol , i'm doing in init:

[self addtarget:self action:@selector(ontouchcancel)forcontrolevents:uicontroleventtouchcancel]; 

how trigger cancel event?

thanks help!

use "uicontroleventtouchupoutside" if want event when finger outside bounds of control.