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[英]How do I dismiss a UIAlertController when the return key is tapped in Swift?
[英]When and where to dismiss UIAlertController in Swift?
我正在调用一个执行URLSession
的方法,但是在执行任何URLSession
之前,它会呈现一个UIAlertController
,该UIAlertController
阻塞UI,直到实现来自请求的某种响应为止。 逻辑告诉我,在主线程上调用UIAlertController
的方法的完成块UIAlertController
其解散是最好的选择。 我认为这是错误的吗? 显然,如此呈现的UIAlertController
确实会显示,但永远不会UIAlertController
。 救命?
块:
getCostandIV { output in
let cost = output["ask"] as! NSNumber
let IV = output["IV"] as! NSNumber
self.enteredCost = cost.stringValue
self.enteredIV = IV.stringValue
DispatchQueue.main.async {
self.progress.dismiss(animated: true, completion: nil)
self.tableView.reloadSections(IndexSet(integer: 1), with: UITableView.RowAnimation.none)
self.canWeSave()
}
}
功能:
func getCostandIV (completionBlock: @escaping (NSMutableDictionary) -> Void) -> Void {
DispatchQueue.main.async {
self.progress = UIAlertController(title: "Retrieving ask price and volatility...", message: nil, preferredStyle: UIAlertController.Style.alert)
self.present(self.progress, animated: true, completion: nil)
}
guard let url = URL(string: "https://api.tdameritrade.com/v1/marketdata/chains?apikey=test&symbol=\(symbol)&contractType=\(type)&strike=\(selectedStrike)&fromDate=\(selectedExpiry)&toDate=\(selectedExpiry)") else {
return
}
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
guard let dataResponse = data,
error == nil else {
//print(error?.localizedDescription ?? "Response Error")
DispatchQueue.main.async {
self.presentedViewController?.dismiss(animated: true, completion: {
let alert = UIAlertController(title: "There was an error retrieving ask price and volatility.", message: "Please try again later.", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "OK", style: .default))
self.present(alert, animated: true)
})
}
return }
do{
//here dataResponse received from a network request
let jsonResponse = try JSONSerialization.jsonObject(with:
dataResponse, options: [])
// //print(jsonResponse) //Response result
guard let jsonDict = jsonResponse as? NSDictionary else {
return
}
// //print(jsonDict)
var strikeMap : NSDictionary = [:]
if self.type == "CALL" {
strikeMap = jsonDict["callExpDateMap"] as! NSDictionary
} else {
strikeMap = jsonDict["putExpDateMap"] as! NSDictionary
}
self.strikes.removeAllObjects()
let inner = strikeMap.object(forKey: strikeMap.allKeys.first ?? "<#default value#>") as! NSDictionary
let innerAgain = inner.object(forKey: inner.allKeys.first ?? "<#default value#>") as! NSArray
let dict : NSDictionary = innerAgain[0] as! NSDictionary
let dict2 = ["ask" : dict["ask"] as! NSNumber, "IV" : dict["volatility"] as! NSNumber] as NSMutableDictionary
completionBlock(dict2)
} catch let parsingError {
print("Error", parsingError)
}
}
task.resume()
}
编辑:使用self.presentedViewController?.dismiss(animated: true, completion: nil)
不能解决此问题。 此外,未调用用于self.progress的dismiss函数的完成块。
编辑2:就算在回调之前在警报控制器上调用了present,在回调函数中的dismiss代码之前,presentedViewController也为零。
只有一切顺利,您的警报才会被取消。 我建议您将功能更改为以下形式:
func getCostandIV (completionBlock: @escaping (NSMutableDictionary?, Error?) -> Void) -> Void
并确保您的completionBlock
是当你的所谓的guard
声明失败或引发错误。 在您当前的代码中,仅在网络请求失败时才解除警报,而在解析JSON时出现问题时则不会解除。
如果getCostandIV
调用getCostandIV
方法,则不会显示第二个警报,并且self.progress
将引用未显示的警报。
更改
self.progress.dismiss(animated: true, completion: nil)
至
self.presentedViewController?.dismiss(animated: true, completion: nil)
使用此方法,要消除警报,应在异步块中添加dismiss方法,并为此设置计时器,应告诉异步块从现在开始到5秒开始异步,然后执行以下操作:
alert.addAction(UIAlertAction(title: "ok", style: .default,
handler: nil))
viewController.present(alert, animated: true, completion: nil)
// change to desired number of seconds (in this case 5 seconds)
let when = DispatchTime.now() + 5
DispatchQueue.main.asyncAfter(deadline: when){
// your code with delay
alert.dismiss(animated: true, completion: nil)
}
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