我如何在Swift中进行异步回调？我正在为我的应用程序编写一个小框架，因为它应该在iOS和OS X上运行。因此，我将不特定于设备的主要代码放入了这个框架中，该框架还处理对我的在线API的请求。显然，我也希望应用程序的GUI（图形用户界面），因此我的ViewControllers可以在API请求完成后立即响应。在Objective-C中，我通过将包含需要调用的函数的视图保存在id变量中，并将函数本身保存在选择器变量中来实现这一点。然后，我使用以下代码调用该函数：
SEL selector = callbackMethod;
((void (*)(id, SEL))[callbackViewController methodForSelector:selector])(callbackViewController, selector);
我该如何在Swift中完成这个任务？或者有更好的方法吗？
非常感谢您的帮助！
我已经在下面的gist中分享了我在这种情况下使用的模式：https://gist.github.com/szehnder/84b0bd6f45a7f3f99306
基本上，我创建了一个名为DataProvider.swift的单例对象来设置一个AFNetworking客户端。然后视图控制器调用该DataProvider上的方法，每个方法都以我定义为ServiceResponse的闭包类型别名结束。这个闭包返回一个字典或一个错误。
通过这种方式，你可以非常清晰地从VC中调用异步数据操作，并明确指示当异步响应返回时要执行什么操作（在我看来）。
DataProvider.swift
typealias ServiceResponse = (NSDictionary?, NSError?) -> Void
class DataProvider: NSObject {
var client:AFHTTPRequestOperationManager?
let LOGIN_URL = "/api/v1/login"
class var sharedInstance:DataProvider {
struct Singleton {
static let instance = DataProvider()
}
return Singleton.instance
}
func setupClientWithBaseURLString(urlString:String) {
client = AFHTTPRequestOperationManager(baseURL: NSURL.URLWithString(urlString))
client!.operationQueue = NSOperationQueue.mainQueue()
client!.responseSerializer = AFJSONResponseSerializer()
client!.requestSerializer = AFJSONRequestSerializer()
}
func loginWithEmailPassword(email:String, password:String, onCompletion: ServiceResponse) -> Void {
self.client!.POST(LOGIN_URL, parameters: ["email":email, "password":password] , success: {(operation:AFHTTPRequestOperation!, responseObject:AnyObject!) -> Void in
self.setupClientWithBaseURLString("http://somebaseurl.com")
let responseDict = responseObject as NSDictionary
// Note: This is where you would serialize the nsdictionary in the responseObject into one of your own model classes (or core data classes)
onCompletion(responseDict, nil)
}, failure: {(operation: AFHTTPRequestOperation!, error:NSError!) -> Void in
onCompletion(nil, error)
})
}
}
MyViewController.swift
import UIKit
class MyViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated)
DataProvider.sharedInstance.loginWithEmailPassword(email:"some@email.com", password:"somepassword") { (responseObject:NSDictionary?, error:NSError?) in
if (error) {
println("Error logging you in!")
} else {
println("Do something in the view controller in response to successful login!")
}
}
}
}
callback(err, data)而不是callback(data, err)。 - bicyclefunc getUsers(completion: (result: NSArray?, error: NSError?)->())
{
var session = NSURLSession.sharedSession()
var task = session.dataTaskWithRequest(request){
(data, response, error) -> Void in
if error != nil {
completion(nil, error)
} else {
var result:NSArray = data to NSArray;
completion(result, nil)
}
}
task.resume()
}
Objective-C:
...
typedef void (^CBSuccessBlock)(id result);
typedef void (^CBFailureBlock)(NSError *error);
...
- (void)usersWithSucces:(CBSuccessBlock)success failure:(CBFailureBlock)failure
{
NSURLSession *session = [NSURLSession sharedSession];
[[session dataTaskWithURL:[NSURL URLWithString:url]
completionHandler:^(NSData *data,
NSURLResponse *response,
NSError *error) {
NSArray *users = //convert data to array
if(error)
failure(error);
else
success(users);
}] resume];
}
Objc:
[api usersWithSucces:^(id result)
{
//Success callback
} failure:^(NSError *error)
{
//Failure callback
}];
Swift:
api.getUsers({(result: AnyObject?, error: NSError?) -> Int in
// callback here
})
更新：
与此同时，我发现这个问题和答案仍然有用并且令人感兴趣。下面是使用泛型枚举作为结果对象的Swift实现的更新版本：
//Generic enum that represents the result
enum AsyncResult<T>
{
case Success(T)
case Failure(NSError?)
}
class CustomUserObject
{
}
func getUsers(completion: (AsyncResult<[CustomUserObject]>)->())
{
let request = NSURLRequest()
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request){
(data, response, error) -> Void in
if let error = error
{
completion(AsyncResult.Failure(error))
} else {
let result: [CustomUserObject] = []//deserialization json data into array of [CustomUserObject]
completion(AsyncResult.Success(result))
}
}
task.resume()
}
//Usage:
getUsers { (result) in
switch result
{
case .Success(let users):
/* work with users*/
break
case .Failure(let error):
/* present an error */
break
}
}
我刚刚做了这个小例子： Swift:异步回调块模式示例
基本上有一个ClassA：
//ClassA it's the owner of the callback, he will trigger the callback when it's the time
class ClassA {
//The property of that will be associated to the ClassB callback
var callbackBlock : ((error : NSError?, message : String?, adress : String? ) -> Void)?
init() {
//Do Your staff
}
//Define your function with the clousure as a parameter
func yourFunctionWithCallback(#functionCallbackParameter : (error : NSError?,message : String?, adress : String?) -> ()) {
//Set the calback with the calback in the function parameter
self.callbackBlock = functionCallbackParameter
}
//Later On..
func callbackTrigger() {
self.callbackBlock?(error: nil,message: "Hello callback", adress: "I don't know")
}
}
而且 ClassB：
//ClassB it's the callback reciver the callback
class ClassB {
@IBAction func testCallbackFunction(sender: UIButton) {
let classA = ClassA()
classA.yourFunctionWithCallback { (error, message, adress) -> () in
//Do your stuff
}
}
}
NSThread能帮助你吗？：
NSThread.detachNewThreadSelector(<#selector: Selector#>, toTarget: <#AnyObject?#>, withObject: <#AnyObject?#>)
((void (*)(id, SEL))objc_msgSend)(callbackViewController, selector);或者只是[callbackViewController performSelector:selector];。 - newacctviewController.performSelector(onMainThread: selector, with: nil, waitUntilDone: false)- Noor