remove “one” action from multi actions in target-action UIbutton

问题

[_btt1 addTarget:self action:@selector(clicked:) forControlEvents:UIControlEventTouchUpInside];
[_btt1 addTarget:self action:@selector(clicked2:) forControlEvents:UIControlEventTouchUpInside];

There are 2 actions in _btt1.

2013-05-31 10:33:31.300 testTargetAndSelector[6029:c07] actions : (
    "clicked:",
    "clicked2:"
)

I remove clicked2 action like this.

[_btt1 removeTarget:self action:@selector(clicked2:) forControlEvents:UIControlEventTouchUpInside];

but there is no action in _btt1.

2013-05-31 10:33:32.731 testTargetAndSelector[6029:c07] actions : (null)

How can I remove single action from multi Actions?

来源：https://stackoverflow.com/questions/16848613/remove-one-action-from-multi-actions-in-target-action-uibutton