Hide uinavigation Leftbar button

i am try for hide uinavigationbar Leftbarbutton

 self.navigationItem.leftBarButtonItem.hidden = YES;

 self.navigationController.navigationItem.leftBarButtonItem.hidden =YES开发者_开发百科; 

I write this code but it is not work for me any body know about it.

self.navigationItem.hidesBackButton = YES;