在Swift中链接多个异步函数 [英] Chaining multiple async functions in Swift

问题描述

我想写一系列函数来验证用户的信息，然后再请求他们确认。 （想象购物应用程式）。

1. 我必须先检查使用者是否已新增卡片。


2. 然后，我必须检查他们是否有足够的余额。


3. 然后，我可以要求他们确认付款。

我可以写异步方法来检查卡的样子...

  func checkHasCard完成：（Bool） - >（））{
 //转到互联网
 //获取卡
 //进程数据
让hasCard：Bool = /用户是否有卡。 
完成（hasCard）
} 
  

  checkHasCard {
 hasCard in 
 if hasCard {
 print（YAY！ ）
} else {
 print（BOO！）
} 
} 
  

$ b b

但是...现在，基于我必须做各种事情。如果用户有卡，我然后需要继续向前，并检查是否有足够的余额（以大致相同的方式）。如果用户没有卡，我会为他们添加他们的卡的屏幕。

但它变得凌乱...

<$ c $ p> checkHasCard {
hasCard in
if hasCard {
// check balance
print（YAY！ b $ b checkBalance {
hasBalance in
if hasBalance {
// WHAT IS GOING ON ?!
print（）
} else {
//请求充值帐户
print（BOO！）
}
}
} else {
//请求卡详细信息
print（BOO！）
}
}
pre>

我想要的是沿着这条线的东西。

  checkHasCard（）//如果没有卡然后显示卡详细信息屏幕
 .checkBalance（）//只有在有卡时运行...如果没有余额请求充值
 .confirmPayment（）
  

这看起来更像swifty，但我不知道如何更近

有办法吗？

解决方案

异步操作，有序和依赖？

你当然可以使用GCD连接任务：

  DispatchQueue.main.async {
 //做某事
 //检查某事... 
 //然后：
 DispatchQueue.main.async {
 //从更高的闭包接收信息
 //等等
} 
} 
  

b $ b

但是如果你的操作很复杂，例如他们有代表，那个架构完全崩溃了。 NSOperation允许复杂的操作以你以后的方式封装。

I'm trying to write a series of functions that will validate the user's information before asking them to confirm something. (Imagine a shopping app).

1. I first have to check that the user has added a card.
2. Then I have to check that they have sufficient balance.
3. Then I can ask them to confirm the payment.

I can write the async method to check the card something like ...

func checkHasCard(completion: (Bool) -> ()) {
    // go to the inter webs
    // get the card
    // process data
    let hasCard: Bool = // the user has a card or not.
    completion(hasCard)
}

This can be run like this...

checkHasCard {
    hasCard in
    if hasCard {
        print("YAY!")
    } else {
        print("BOO!")
    }
}

But... now, based off that I have to do various things. If the user does have a card I then need to continue onwards and check there is sufficient balance (in much the same way). If the user does not have a card I present a screen for them to add their card.

But it gets messy...

checkHasCard {
    hasCard in
    if hasCard {
        // check balance
        print("YAY!")
        checkBalance {
            hasBalance in
            if hasBalance {
                // WHAT IS GOING ON?!
                print("")
            } else {
                // ask to top up the account
                print("BOO!")
            }
        }
    } else {
        // ask for card details
        print("BOO!")
    }
}

What I'd like instead is something along the lines of this...

checkHasCard() // if no card then show card details screen
    .checkBalance() // only run if there is a card ... if no balance ask for top up
    .confirmPayment()

This looks much more "swifty" but I'm not sure how to get closer to something like this.

Is there a way?

解决方案

Asynchronous operations, ordered and with dependencies? You're describing NSOperation.

Certainly you can chain tasks using GCD:

DispatchQueue.main.async {
    // do something
    // check something...
    // and then:
    DispatchQueue.main.async {
        // receive info from higher closure
        // and so on
    }
}

But if your operations are complex, e.g. they have delegates, that architecture completely breaks down. NSOperation allows complex operations to be encapsulated in just the way you're after.

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