如何在对象内部知道异步函数何时完成

Question

我有一个包含对象的类，为了使用对象的属性，NSURLSession必须完成其异步数据请求。我该如何通过对象创建回调，以了解该函数何时完成，并可以调用这些属性。

Answer 1

您没有给出代码的示例，所以我将抽象地编写。您需要在NSURLSession对象的完成中调用与您的对象一起工作的方法。例如，它可能看起来像这样：

// This is your object
struct SomeData {
        var someValue: Int = 0
    }
// This is class that use it
class Foo {
    var someData: SomeData
    init() {
        someData = SomeData()
        requestData()
    }
    // This is your function that need to wait for the request
    func doActionWithData() {
        print(someData.someValue)
    }
    // This is request
    func requestData() {
        // Make request with your params
        let request = NSMutableURLRequest(...)
        ...
        // For example you do it like this
        NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: { (data, response, error) in
            // here you have data for your object you can get it from 
            // response and then call function to work with it
            self.someData.someValue = ...
            self.doActionWithData()
        })
    }
}