如何在PromiseKit中设置when(fulfilled :)? [英] How to set up when(fulfilled:) in PromiseKit?

问题描述

我设置了一个返回Promise<PFObject>的函数.我想在PromiseKit的when(fulfilled:)功能中使用此功能，但是每当尝试这样做时，都会出现错误.这是返回Promise<PFObject>的函数:

I have a function set up to return a Promise<PFObject>. I would like to use this function in PromiseKit's when(fulfilled:) functionality, but whenever I try to do so, I get an error. Here is the function which returns the Promise<PFObject>:

func Query() -> Promise<PFObject>{
        return Promise{ fulfill, reject in
            let linkQueryy = PFUser.query()
            linkQueryy?.findObjectsInBackground(block: { (objectss, error) in
                if let objects = objectss{
                    for object in objects{
                        fulfill(object)
                    }
                }
            })
        }
    }

如您所见，该函数在实现时会返回Promise.因此，我尝试在我的viewDidLoad()中设置一个when语句，如下所示:

As you can see, the function returns the Promise upon fulfillment. Thus, I tried to set up a when statement in my viewDidLoad() as follows:

override func viewDidLoad() {
        super.viewDidLoad()

        when(fulfilled: Query()).then{
            //do more asynch stuff
        }
    }

但是，我得到一个错误，即xcode无法使用参数列表类型为'(fulfilled:Promise<PFObject>)'调用'when'，".我不知道如何解决此问题，因为我认为我已正确设置了它. when需要一个承诺，而我正在给它一个承诺，所以我不确定该怎么做.

However, I get the error that xcode cannot "invoke 'when' with an argument list type of '(fulfilled: Promise<PFObject>)'". I do not know how to fix this as I thought I had it set up correctly. The when needs a promise, and I am giving it one so I am not sure what to do.

推荐答案

尝试如下:

when(fulfilled: [linkQueryy()] as! [Promise<Any>]).then { _ in
    // do more asynch stuff
}

参数fulfilled:必须是可迭代的.

顺便说一句，when(fulfilled:)仅在您有很多承诺并且需要等待所有成功完成时才是必需的.但是在您的代码中，您只需要等待一个诺言即可.

By the way, when(fulfilled:) is necessary only when you have many promises and need wait for all to complete successfully. But in your code, you need to wait for only one promise.

对于单个承诺，更好的方法是形成如下链:

For a single promise, the better way is to form a chain as follows :

firstly {
    linkQueryy()
}.then { _ -> Void in
    // do more asynch stuff
}.catch { _ in
    // error!
}

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