完成處理程序不能按預期的方式在Swift中工作

-1

使用完成處理程序時，我有以下兩個函數。問題在第二個函數的註釋中突出顯示...爲什麼result部分甚至在功能checforViolationStatus()中的異步調用完成之前得到執行。完成處理程序不能按預期的方式在Swift中工作

func checkViolationStatus(usr: PFUser, completion: (result: Int32) -> Void) { 
    var violations: Int32 = 0 
    var query = PFQuery(className: PF_BLOCKEDUSERS_CLASS_NAME) 
    query.whereKey(PF_BLOCKEDUSERS_USER, equalTo: usr) 


    query.countObjectsInBackgroundWithBlock { 
     (count: Int32, error: NSError?) -> Void in 
     if error == nil { 
      print("Result = \(count)") 

      //The result here returned is 4, I can see it but always ZERO(0) gets printed in the main function. Unable to understand why. 
      violations = count 
     } 
    } 

    completion(result: violations) 

} 


    func goToMainMenu() { 

    if PFUser.currentUser() != nil { 

     self.mCould.checkViolationStatus(PFUser.currentUser()!) { 
      (result: Int32) in 

      //QUESTION: result is getting returned as ZERO even before the actual asynchronous call in the checkforViolation function has been completed - why???? 

      if result < 4 { 
       //Go to Main Menu Screen 
       print("result<=4 so calling segue") 
       self.performSegueWithIdentifier("segueLoginVCToMainVC", sender: nil) 
      } else { 
       print("result >=4, so should not be doing anything") 
      } 

      print("Number of Violations Received Back: \(result)") 

     } 
    } 


}

來源

2015-10-19 user1406716

Downvoted因爲你做完全一樣的錯誤，因爲在你前面的問題，沒有做什麼，我這麼認真在我的答案解釋那裏。 – matt

是的，傻我。是的，你是對的。希望你添加它作爲答案，會標記它。 – user1406716

試着改變你的函數，你應該在countObjectsInBackgroundWithBlock調用completion，這種方法是異步。

或者countObjectsInBackgroundWithBlock之前這個函數返回後完成

func checkViolationStatus(usr: PFUser, completion: (result: Int32) -> Void) { 
var violations: Int32 = 0 
var query = PFQuery(className: PF_BLOCKEDUSERS_CLASS_NAME) 
query.whereKey(PF_BLOCKEDUSERS_USER, equalTo: usr) 


query.countObjectsInBackgroundWithBlock { 
    (count: Int32, error: NSError?) -> Void in 
    if error == nil { 
     print("Result = \(count)") 

     //The result here returned is 4, I can see it but always ZERO(0) gets printed in the main function. Unable to understand why. 
     violations = count 
     completion(result: violations) 

    } 
} 
}

來源

2015-10-19 02:07:38 Leo

完成處理程序不能按預期的方式在Swift中工作

回答

相關問題