ios - UINavigationController is nil after pop -

my project complex (a bit probably) question simple, here's code

... self.vc = [[classname alloc] init]; if ([[self.navigationcontroller.viewcontrollers lastobject] iskindofclass:[classname class]]) {     [self backandgo:self.vc title:@"title"]; } else {     [self vai:self.vc title:@"title"]; } ... 

in code i've go directly in next view if current view different classname, otherwise go of 1 view , go next.

- (void)backandgo:(id)view title:(nsstring *)title

- (void)backandgo:(id)view title:(nsstring *)title {     nslog(@"before %@,%d",[self.navigationcontroller viewcontrollers],[[self.navigationcontroller viewcontrollers] count]);      [self.navigationcontroller popviewcontrolleranimated:no];      alcparentviewcontroller *viewcontroller = (alcparentviewcontroller *)view;     [self.navigationcontroller pushviewcontroller:viewcontroller animated:yes];      nslog(@"after %@,%d",[self.navigationcontroller viewcontrollers],[[self.navigationcontroller viewcontrollers] count]); } 

alcparentviewcontroller parent class of vc, in method first log of navigatin controller correct stack of viewcontrollers, , popviewcontroller executed in second log navigationcontroller null 0 element obviously, , pushviewcontroller method not executed, why? ideas?

- (void)vai:(id)view title:(nsstring *)title

- (void)vai:(id)view title:(nsstring *)title {            alcparentviewcontroller *viewcontroller = (alcparentviewcontroller *)view;     [self.navigationcontroller pushviewcontroller:viewcontroller animated:yes]; } 

this instead other method reach directly second view, , works correctly, courius thing (almost me) dispite nil pushviewcontroller, navigation (push , pop) in other view works correctly...

edit 1:

as lucaslt89 said i've put breakpoint in second log , make "po self.navigationcontroller" in consolle, here result

(lldb) po self.navigationcontroller $0 = 0x00000000 <nil> (lldb) 

it's nil, can see in log without breakpoint...

edit 2:

(lldb) po self.navigationcontroller $0 = 0x099787d0 <uinavigationcontroller: 0x99787d0> (lldb) po auxnavcontroller $1 = 0x099787d0 <uinavigationcontroller: 0x99787d0> (lldb) 

after operations suggested lucaslt89, 2 address same

according last edit, 1 solution hold reference navigation controller. backandgo method should that

- (void)backandgo:(id)view title:(nsstring *)title {     nslog(@"before %@,%d",[self.navigationcontroller viewcontrollers],[[self.navigationcontroller viewcontrollers] count]);      uinavigationcontroller *auxnavcontroller = self.navigationcontroller;      [self.navigationcontroller popviewcontrolleranimated:no];      alcparentviewcontroller *viewcontroller = (alcparentviewcontroller *)view;     [auxnavcontroller pushviewcontroller:viewcontroller animated:yes];      nslog(@"after %@,%d",[auxnavcontroller viewcontrollers],[[auxnavcontroller viewcontrollers] count]); } 

if debug that, address of self.navigationcontroller prior pop should same auxnavcontroller after pop. try , tell results!