[英]Completion handler not working as expected in Swift
I have these two functions below, using a completion handler.我在下面有这两个函数,使用完成处理程序。 The questions is highlighted in comments of the 2nd function... why is the
result
part getting executed even before the asynchronous call in function checforViolationStatus()
been completed.问题在第二个函数的注释中突出显示......为什么即使在函数
checforViolationStatus()
的异步调用完成之前, result
部分也会被执行。
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)")
}
}
}
Try change your function to this,you should call completion
in the countObjectsInBackgroundWithBlock
,this method is async.尝试将您的功能更改为此,您应该在
countObjectsInBackgroundWithBlock
调用completion
,此方法是异步的。
Or this function return before countObjectsInBackgroundWithBlock
is finished或者这个函数在
countObjectsInBackgroundWithBlock
完成之前返回
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)
}
}
}
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.