Edit
Based on your comment
I added the tabbarcontroller using, tabctrl.view.frame = CGRectMake(0, 20, 320, 548); [self.view addSubview:tabctrl.view];
You should also initialize the tabBar with window bounds or self.view or try not setting the view and tabbar will set it itself
Previous Answer
Enable FullScreen for the MainWindow in the utilities inspector