在下面的这段代码中,我调用了函数 displayMyAlertMessage() 两次。我调用的第一个工作完美,但第二个给了我一个错误,说该函数只能从主线程调用。在我的情况下我该怎么做?
我正在使用这段代码:
@IBAction func loginButtonTapped(sender: AnyObject) {
result2Value = ""
let userEmail = userEmailTextField.text
let userPassword = userPasswordTextField.text
if userPassword.isEmpty || userPassword.isEmpty {
displayMyAlertMessage("All fields are required")
return;
}
//send user data to server side
let myUrl = NSURL(string: "http://www.avanta.com/extra/test-userLogin.php")
let request = NSMutableURLRequest(URL:myUrl!)
request.HTTPMethod = "POST"
let postString = "email=\(userEmail)&password=\(userPassword)"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request){
data, response, error in
if error != nil{
println("error\(error)")
return
}
var err:NSError?
var json = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: &err) as? NSDictionary
if let parseJSON = json {
var resultValue:String = parseJSON["status"] as! String!
println("result: \(resultValue)")
if (resultValue == "Success") {
//login succesful
NSUserDefaults.standardUserDefaults().setBool(true, forKey: "isUserLogin")
NSUserDefaults.standardUserDefaults().synchronize()
self.dismissViewControllerAnimated(true, completion: nil)
// return
}
else{
self.displayMyAlertMessage("Wrong name or password")
}
}
}
task.resume()
}
调用这个函数:
func displayMyAlertMessage(userMessage:String){
var myAlert = UIAlertController(title:"Alert", message:userMessage, preferredStyle: UIAlertControllerStyle.Alert)
let okAction = UIAlertAction(title:"Ok", style:UIAlertActionStyle.Default, handler:nil)
myAlert.addAction(okAction)
self.presentViewController(myAlert, animated:true, completion:nil)
}
我得到的错误:
2015-06-20 14:44:41.646 UserLoginAndRegistration[6064:750474] *** Assertion failure in -[UIKeyboardTaskQueue waitUntilAllTasksAreFinished], /SourceCache/UIKit/UIKit-3318.16.14/Keyboard/UIKeyboardTaskQueue.m:374
2015-06-20 14:44:41.657 UserLoginAndRegistration[6064:750474] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '- [UIKeyboardTaskQueue waitUntilAllTasksAreFinished] may only be called from the main thread.'
*** First throw call stack:
(0x186551e48 0x196c4c0e4 0x186551d08 0x1873d5554 0x18ad2b0a8 0x18ad2b734 0x18ad24a1c 0x18b251564 0x18b0156a8 0x18b0169e4 0x18b0188dc 0x18adee0b4 0x100028f9c 0x10002b500 0x10002b5f4 0x10002b624 0x10002b68c 0x185ee6540 0x187407508 0x187358c94 0x18734861c 0x18740a26c 0x1005a4df0 0x1005af854 0x1005a8120 0x1005b175c 0x1005b2f18 0x19746d2e4 0x19746cfa8)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)
最佳答案
您必须始终从主队列更新 UI 元素,有时在您不这样做时可以正常工作,但大多数时候您的应用程序会出现奇怪的行为,幸运的是编译器会警告您,有时需要几天时间才能发现这样的错误当事情不起作用时
使用下面的代码调用和关闭您的警报 View
dispatch_async(dispatch_get_main_queue()) {
self.dismissViewControllerAnimated(true, completion: nil)
}
dispatch_async(dispatch_get_main_queue()) {
self.displayMyAlertMessage("Wrong name or password")
}
您可以在 Grand Central Dispatch (GCD) Reference 查看更多详细信息
关于函数只能在主线程中调用,为什么呢?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30954254/