Ios 如何顺序执行两个异步函数
} 我已经得到了这个代码,但是,我想在它之后运行另一个函数。我该怎么办。比如:Ios 如何顺序执行两个异步函数,ios,swift,asynchronous,dispatch,Ios,Swift,Asynchronous,Dispatch,} 我已经得到了这个代码,但是,我想在它之后运行另一个函数。我该怎么办。比如: func getTopicIdFromMYSQL(){ let myUrl = NSURL(string: "xxxx") let request = NSMutableURLRequest(URL: myUrl!) request.HTTPMethod = "POST" let email:String = "xxx@gmail.com" let postString = "
func getTopicIdFromMYSQL(){
let myUrl = NSURL(string: "xxxx")
let request = NSMutableURLRequest(URL: myUrl!)
request.HTTPMethod = "POST"
let email:String = "xxx@gmail.com"
let postString = "email=\(email)"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request){
data, response, error in
if(error != nil){
print("Get all topic")
print("error=\(error)")
return
}
do {
let json = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as? NSDictionary
if let parseJSON = json
{
let resultValue = parseJSON["status"] as? String
print("Get all topic")
favouriteTopic = parseJSON["getResult"]! as! [AnyObject]
print("return topic:\(favouriteTopic)")
dispatch_async(dispatch_get_main_queue(), {
if(resultValue == "Success"){
}
else{
let error = UIAlertController(title: "Error", message: "Please check your network configuration!:-(", preferredStyle: .Alert)
let cancel = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
let ok = UIAlertAction(title: "OK", style: .Default, handler: nil)
error.addAction(cancel)
error.addAction(ok)
}
})
}
}catch
{
print(error)
}
}
task.resume()
我发现问题是我的代码没有按顺序执行,函数getCommentFromMYSQL几乎与GetTopIdFromMySQL相同,我想按顺序运行这三个函数,我该怎么办?代码总是按顺序执行。我认为您的问题在于您在这一行中进行异步调用:
getTopicIdFromMYSQL()
getCommentFromMYSQL()
print("Finish")
但是,由于代码是按顺序执行的,因此在异步调用完成之前会调用方法getCommentFromMYSQL()
。您应该在以下条件中调用getCommentFromMYSQL()
:
NSURLSession.sharedSession().dataTaskWithRequest(request)
或者你想什么时候都行。这将确保在第一个方法完成其执行后调用方法
getCommentFromMYSQL()
。这是因为,您正在进行异步调用,该调用在后台线程中运行
如果要按顺序执行,请在分派到主队列后调用下一个方法
if (resultValue == "Success") {
}
将完成处理程序作为参数添加到异步函数中:
dispatch_async(dispatch_get_main_queue(), {
//call here
getCommentFromMYSQL()
if(resultValue == "Success"){
}
else{
let error = UIAlertController(title: "Error", message: "Please check your network configuration!:-(", preferredStyle: .Alert)
let cancel = UIAlertAction(title: "Cancel", style: .Cancel, handler: nil)
let ok = UIAlertAction(title: "OK", style: .Default, handler: nil)
error.addAction(cancel)
error.addAction(ok)
}
})
注意:
当异步函数完成时,必须最终调用完成处理程序——要么是错误,要么是计算值
然后按如下所示调用这些函数:
func getTopicIdFromMYSQL(completion: (AnyObject?, ErrorType?)->())
func getCommentFromMYSQL(completion: (AnyObject?, ErrorType?)->())
您可以按如下方式实现这些功能:
getTopicIdFromMYSQL() { (result1, error) in
if let result1 = result1 {
// process result1
// ...
getCommentFromMYSQL() { (result2, error) in
if let result2 = result2 {
// process result2
// ...
} else {
// handle error
}
}
} else {
// handle error
}
}
将它们转换为NSOperations,使每个操作都依赖于上一个操作。WWDC 15有一段很好的视频
func getTopicIdFromMYSQL(completion: (AnyObject?, ErrorType?) {
let myUrl = NSURL(string: "xxxx")
let request = NSMutableURLRequest(URL: myUrl!)
request.HTTPMethod = "POST"
let email:String = "xxx@gmail.com"
let postString = "email=\(email)"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
let task = NSURLSession.sharedSession().dataTaskWithRequest(request){
data, response, error in
if error != nil {
completion(nil, error)
}
do {
let json = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as? NSDictionary
if let parseJSON = json {
let resultValue = parseJSON["status"] as? String
print("Get all topic")
favouriteTopic = parseJSON["getResult"]! as! [AnyObject]
completion(favouriteTopic, nil)
} else {
throw MyError.Error(message: "bogus JSON")
}
} catch let error {
completion(nil, error)
}
}
task.resume()
}