NSURLConnection sendAsynchronousRequest 无法从关闭中获取变量 [英] NSURLConnection sendAsynchronousRequest can't get variable out of closure
问题描述
我正在尝试使用 POST 从 PHP 页面获取简单的文本响应.我有以下代码:
I'm trying to get a simple text response from a PHP page using POST. I have the following code:
func post(url: String, info: String) -> String {
var URL: NSURL = NSURL(string: url)!
var request:NSMutableURLRequest = NSMutableURLRequest(URL:URL)
var output = "Nothing Returned";
request.HTTPMethod = "POST";
var bodyData = info;
request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding);
NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()){
response, data, error in
output = (NSString(data: data, encoding: NSUTF8StringEncoding))!
}
return output
}
虽然这段代码没有抛出任何错误,但当我像这样调用它时:
While this code does not throw any errors, when I make a call to it like this:
println(post(url, info: data))
它只打印:Nothing Returned",即使我要更改行:
It only prints: "Nothing Returned" even though if I were to change the line:
output = (NSString(data: data, encoding: NSUTF8StringEncoding))!
为此:
println((NSString(data: data, encoding: NSUTF8StringEncoding)))
它确实打印出正确的响应.我这里的变量有问题吗?
it does print out the proper response. Am I doing something wrong with my variables here?
推荐答案
这是调用使用完成处理程序块/闭包的异步函数.因此,您需要在自己的代码中使用完成处理程序模式.这包括将方法返回类型更改为 Void
并添加一个新的 completionHandler
闭包,该闭包将在异步调用完成时调用:
This is calling asynchronous function that is using a completion handler block/closure. So, you need to employ the completion handler pattern in your own code. This consists of changing the method return type to Void
and adding a new completionHandler
closure that will be called when the asynchronous call is done:
func post(url: String, info: String, completionHandler: (NSString?, NSError?) -> ()) {
let URL = NSURL(string: url)!
let request = NSMutableURLRequest(URL:URL)
request.HTTPMethod = "POST"
let bodyData = info
request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding);
NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) { response, data, error in
guard data != nil else {
completionHandler(nil, error)
return
}
completionHandler(NSString(data: data!, encoding: NSUTF8StringEncoding), nil)
}
}
或者,由于 NSURLConnection
现在已被正式弃用,最好使用 NSURLSession
:
Or, since NSURLConnection
is now formally deprecated, it might be better to use NSURLSession
:
func post(url: String, info: String, completionHandler: (NSString?, NSError?) -> ()) -> NSURLSessionTask {
let URL = NSURL(string: url)!
let request = NSMutableURLRequest(URL:URL)
request.HTTPMethod = "POST"
let bodyData = info
request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding);
let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
dispatch_async(dispatch_get_main_queue()) {
guard data != nil else {
completionHandler(nil, error)
return
}
completionHandler(NSString(data: data!, encoding: NSUTF8StringEncoding), nil)
}
}
task.resume()
return task
}
你这样称呼它:
post(url, info: info) { responseString, error in
guard responseString != nil else {
print(error)
return
}
// use responseString here
}
// but don't try to use response string here ... the above closure will be called
// asynchronously (i.e. later)
注意,为了保持简单,我采用了尾随闭包语法(请参阅 The Swift Programming Language: Closures),但希望它能说明这个想法: 不能立即返回异步方法的结果,因此提供一个完成处理程序闭包,在异步方法完成时将调用该闭包.
Note, to keep this simple, I've employed the trailing closure syntax (see Trailing Closure section of The Swift Programming Language: Closures), but hopefully it illustrates the idea: You cannot immediately return the result of an asynchronous method, so provide a completion handler closure that will be called when the asynchronous method is done.
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