ios - UIBarButtonItem not appearing -

my app layout follows -

the rootviewcontroller tabviewcontroller 3 tabs each having uinavigationcontroller rootviewcontroller. within 1 of these tabs pushing upon cell selection tabcontroller has 2 tabs. trying set rightbarbuttonitem on each of these 2 tab's viewcontrollers... in viewdidload method of both of these doing:

self.navigationitem.rightbarbuttonitem = [[uibarbuttonitem alloc] initwithbarbuttonsystemitem:uibarbuttonsystemitemedit target:self action:@selector(selectionchanged:)]; 

however doing absolutely nothing! thought apple documentations set navigationitem's rightbarbuttonitem anywhere within navigation controllers view hierarchy doesn't seem case here. idea - if - doing wrong?

the solution instead of setting rightbarbuttonitem on self.navigationitem need set on parent tabbarcontroller :

self.tabbarcontroller.navigationitem.rightbarbuttonitem = [[uibarbuttonitem alloc] initwithbarbuttonsystemitem:uibarbuttonsystemitemedit target:self action:@selector(selectionchanged:)];