ios - (Firebase) Assign value to global variable from a returned completion handler function -

i have function retrieves "users" node of firebase database, , trying assign global variable equal number of users in "users" node so:

func getusers(completionhandler:@escaping (int) -> ()) {      let ref = database.database().reference().child("users")      ref.observe(.childadded, with: { (snapshot) in         if let dictionary = snapshot.value as? [string: anyobject] {              let user = user()              user.id = snapshot.key             user.setvaluesforkeys(dictionary)                             self.users.append(user)             completionhandler(self.users.count)         }      }, withcancel: nil)  } 

then, in viewdidload() function, try assign global variable equal number of users in "users" node this:

var usercount: int?  override func viewdidload() {     super.viewdidload()      getusers(){ (count) in         self.usercount = count     }      print(usercount) } 

this prints nil, , should 12, amount of users added firebase database. since unfamiliar completion handlers, unsure how fix this.

any , appreciated.

your completion closure @escaping async reason print(usercount) executed before completion block returns , getting nil. try this:

var usercount: int?  override func viewdidload() {     super.viewdidload()      getusers(){ (count) in         self.usercount = count         print(self.usercount)     } } 

or can remove @escaping , make completion closure sync.

func getusers(completionhandler:(int) -> ()) {      let ref = database.database().reference().child("users")      ref.observe(.childadded, with: { (snapshot) in         if let dictionary = snapshot.value as? [string: anyobject] {              let user = user()              user.id = snapshot.key             user.setvaluesforkeys(dictionary)                             self.users.append(user)             completionhandler(self.users.count)         }      }, withcancel: nil)  }