Swift 闭包返回值(以前的completionBlock)
我想在长期操作完成后返回一些值。 但是,此外,我想将逻辑和gui分开 比如,;我有两节课Swift 闭包返回值(以前的completionBlock),swift,ios8,Swift,Ios8,我想在长期操作完成后返回一些值。 但是,此外,我想将逻辑和gui分开 比如,;我有两节课 SomeServices.swift,其方法名为“getDataFromService…” MyTableViewController.swift将显示“getDataFromService”的结果 因此,在前面的Objective-C中,我刚刚在一些服务中添加了一个方法,如下所示: (void)getDataFromService:(void (^)(NSArray *, NSError *))compl
(void)getDataFromService:(void (^)(NSArray *, NSError *))completionBlock{ ...... }
在这个方法中,我刚刚调用了completionBlock(myData,myError)
将我的值返回给tableviewcontroller
我必须在SomeServices.swift中定义的等效闭包是什么?在MyTableViewController中如何调用它
我知道如何调用这样一个简单的闭包:
....({
responseData, error in
if(!error){
//Do something
}
})
但我不知道如何用completionBlock等价物定义闭包
任何帮助都将不胜感激闭包的好处是,您可以传递任何您想要的内容。方法或函数-这无关紧要 您可以在参数内传递函数,然后调用它
func someFunctionThatTakesAClosure(completionClosure: () -> ()) {
// function body goes here
if(error = false) {
completionClosure()
}
}
//Call it
someFunctionThatTakesAClosure({
//Completions Stuff
println("someFunctionThatTakesAClosure")
});
摘自:苹果公司《Swift编程语言》。iBooks 答案在语言指南中: 假设您想要返回一个字符串。这就是语法
({(responseData: DataClass, error: ErrorClass) -> String in
//do stuff - calculations etc..
return calculatedString
})
下面是一个示例,它获取两个字符串并将它们连接起来,然后返回结果:
let sumStrings = ({(first: String, second: String) -> String in
return first + " " + second
})
然后您可以执行以下操作:
sumStrings("Hello","Swift") // "Hello Swift"
下面是我如何使用singleton ServiceManager来实现这一点
class ServiceManager: NSObject {
// Static Instance variable for Singleton
static var sharedSessionManager = ServiceManager()
// Function to execute GET request and pass data from escaping closure
func executeGetRequest(with urlString: String, completion: @escaping (Data?) -> ()) {
let url = URL.init(string: urlString)
let urlRequest = URLRequest(url: url!)
URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in
// Log errors (if any)
if error != nil {
print(error.debugDescription)
} else {
// Passing the data from closure to the calling method
completion(data)
}
}.resume() // Starting the dataTask
}
// Function to perform a task - Calls executeGetRequest(with urlString:) and receives data from the closure.
func downloadMovies(from urlString: String, completion: @escaping ([Movie]) -> ()) {
// Calling executeGetRequest(with:)
executeGetRequest(with: urlString) { (data) in // Data received from closure
do {
// JSON parsing
let responseDict = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String: Any]
if let results = responseDict!["results"] as? [[String:Any]] {
var movies = [Movie]()
for obj in results {
let movie = Movie(movieDict: obj)
movies.append(movie)
}
// Passing parsed JSON data from closure to the calling method.
completion(movies)
}
} catch {
print("ERROR: could not retrieve response")
}
}
}
}
下面是我如何使用singleton类的示例
ServiceManager.sharedSessionManager.downloadMovies(from: urlBase) { (movies : [Movie]) in // Object received from closure
self.movies = movies
DispatchQueue.main.async {
// Updating UI on main queue
self.movieCollectionView.reloadData()
}
}
我希望这能帮助任何寻找相同解决方案的人。Ha,我先查看了这本书,但完全忽略了这一个例子!谢谢你把它拔出来。正如上面所说的,如果闭包没有返回任何内容,
->()
是必需的。