swift - Difference between before and after in viewDidLoad -

i have tried set searchbar tableheaderview inside of viewdidload:

 override func viewdidload() {     super.viewdidload()       // searchcontroller initializiation     self.searchcontroller = uisearchcontroller.init(searchresultscontroller: nil)     self.searchcontroller.delegate = self     self.searchcontroller.searchbar.delegate = self     self.searchcontroller.searchbar.sizetofit()     self.searchcontroller.searchresultsupdater = self     self.searchcontroller.searchbar.bartintcolor = uicolor.white     self.searchcontroller.searchbar.keyboardappearance = .default     self.searchcontroller.searchbar.backgroundcolor = uicolor.white     self.searchcontroller.hidesnavigationbarduringpresentation = true     self.searchcontroller.obscuresbackgroundduringpresentation = false       self.tableview.tableheaderview = self.searchcontroller.searchbar     self.definespresentationcontext = true      self.fetch()     self.tableview.reloaddata()  } 

and fetch() function:

func fetch() {     let fetchrequest:nsfetchrequest<phone> = phone.fetchrequest()     fetchrequest.sortdescriptors = [nssortdescriptor.init(key: "header", ascending: true), nssortdescriptor.init(key: "date", ascending: true)]      self.fetchedresultscontroller = nsfetchedresultscontroller.init(fetchrequest: fetchrequest, managedobjectcontext: self.managedobjectcontext, sectionnamekeypath: "header", cachename: nil)     self.fetchedresultscontroller.delegate = self      {         try self.fetchedresultscontroller.performfetch()         self.tableview.reloaddata()     } catch {}  } 

but don't understand doesn't work. xcode crashes , nothing happens. , have tried change inside of viewdidload method:

override func viewdidload() {     super.viewdidload()      self.fetch()     self.tableview.reloaddata()      // searchcontroller initializiation     self.searchcontroller = uisearchcontroller.init(searchresultscontroller: nil)     self.searchcontroller.delegate = self     self.searchcontroller.searchbar.delegate = self     self.searchcontroller.searchbar.sizetofit()     self.searchcontroller.searchresultsupdater = self     self.searchcontroller.searchbar.bartintcolor = uicolor.white     self.searchcontroller.searchbar.keyboardappearance = .default     self.searchcontroller.searchbar.backgroundcolor = uicolor.white     self.searchcontroller.hidesnavigationbarduringpresentation = true     self.searchcontroller.obscuresbackgroundduringpresentation = false       self.tableview.tableheaderview = self.searchcontroller.searchbar     self.definespresentationcontext = true    } 

success! works properly. don't understand difference?

it because set delegates searchresultsupdater , searchbar before fetchedresultscontroller initialised. in code searchresultsupdater or searchbar's delegate methods accessing fetchedresultscontroller , getting nil app crashes. suggestion avoid crash make searchresultscontroller computed or lazy property.