swift - Custom Tab Bar button Not hiiding on push -

i have 5 tabs , center button custom, created uitabbarcontroller class customize center button. happening when hidesbottombarwhenpushed tab bar becomes hidden except center custom button still visible & not disabled , when tab

class tabbar: uitabbarcontroller {      @iboutlet weak var centerbutton:uibutton!      override func viewdidload() {         super.viewdidload()          let nimage = uiimage(named: "infobutton")         let bimage = uiimageview(image: nimage!)         bimage.frame.size = cgsize(width: 50, height: 50)           let cbutton: uibutton = uibutton.buttonwithtype(uibuttontype.custom) uibutton         cbutton.autoresizingmask = uiviewautoresizing.flexiblerightmargin | uiviewautoresizing.flexibleleftmargin | uiviewautoresizing.flexibletopmargin | uiviewautoresizing.flexiblebottommargin         cbutton.frame = cgrectmake(0,0, 50, 50)         cbutton.setbackgroundimage(nimage, forstate: uicontrolstate.normal)         cbutton.setbackgroundimage(nimage, forstate: uicontrolstate.highlighted)          cbutton.addtarget(self, action: "buttonpressed:", forcontrolevents: uicontrolevents.touchupinside)         self.centerbutton = cbutton          var heightdifference:cgfloat = bimage.frame.size.height - self.tabbar.frame.size.height         if (heightdifference < 0) {             cbutton.center = self.tabbar.center;         } else {             var center:cgpoint = self.tabbar.center;             center.y = center.y - heightdifference/2.0;             cbutton.center = center           }         self.view.addsubview(cbutton)      }      func buttonpressed(sender:uibutton) {         self.selectedindex = 2     } }