ios - Swift PromiseKit : Equivalent to when() which executes sequentially?
<p><p>我正在使用 PromiseKit 和 Swift，到目前为止它非常方便。他们提供的函数之一是 <code>when()</code>，它允许您拥有一个包含任意数量的 Promise 的数组，并且只有在所有 Promise 都完成后才执行某些操作。</p>
<p>但是，数组中的 Promise 是并行执行的。我还没有找到任何可以让我按顺序执行它们的功能。我尝试编写自己的递归函数，但它似乎没有按照它们在数组中的顺序执行 promise ，并且我偶尔会遇到“Promise deallocated”错误。请帮忙!</p>
<pre><code>static func executeSequentially(promises: ) -> Promise<Void> {
return Promise<Void> { fulfil, reject in
var mutablePromises = promises
if mutablePromises.count > 0 {
mutablePromises.first!
.then { _ -> Promise<Void> in
print("DEBUG: \(mutablePromises.count) promises in promise array.")
mutablePromises.remove(at: 0)
return executeSequentially(promises: mutablePromises)
}.catch { error in
print("DEBUG: Promise chain rejected.")
reject(error)
}
} else {
print("DEBUG: Promise chain fulfilled.")
fulfil(())
}
}
}
</code></pre></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>这是一个扩展，它接受一组 Promise 并返回一个新的 Promise，其中所有单独的 Promise 链接在一起以串行运行。我已经修改了此处找到的版本以与 Swift 5/PromiseKit 7 alpha 一起使用:<a href="https://gist.github.com/kashifshaikh/416b9ffbd300eb680fad3641b6ec53ea" rel="noreferrer noopener nofollow">https://gist.github.com/kashifshaikh/416b9ffbd300eb680fad3641b6ec53ea</a> </p>
<p>原作者随附的帖子可以在这里找到:<a href="https://medium.com/@peatiscoding/promisekit-chaining-3c957a8ace24" rel="noreferrer noopener nofollow">https://medium.com/@peatiscoding/promisekit-chaining-3c957a8ace24</a> </p>
<pre><code>import Foundation
import PromiseKit
extension Promise {
/// Returns a single Promise that you can chain to. Wraps the chains of promises passed into the array into a serial promise to execute one after another using `promise1.then { promise2 }.then ...`
///
/// - Parameter promisesToExecuteSerially: promises to stitch together with `.then` and execute serially
/// - Returns: returns an array of results from all promises
public static func chainSerially<T>(_ promises:[() -> Promise<T>]) -> Promise<> {
// Return a single promise that is fulfilled when
// all passed promises in the array are fulfilled serially
return Promise<> { seal in
var outResults = ()
if promises.count == 0 {
seal.fulfill(outResults)
} else {
let finalPromise:Promise<T>? = promises.reduce(nil) { (r, n) -> Promise<T> in
return r?.then { promiseResult -> Promise<T> in
outResults.append(promiseResult)
return n()
} ?? n()
}
finalPromise?.done { result in
outResults.append(result)
seal.fulfill(outResults)
}.catch { error in
seal.reject(error)
}
}
}
}
}
</code></pre>
<p>用法:</p>
<pre><code>let serialSavePromises: [() -> Promise<Bool>] = allImages.map { image in
return { in
guard let self = self else { return .value(false) }
return self.saveImage(image)
}
}
return Promise<>.chainSerially(serialSavePromises)
</code></pre></p>
<p style="font-size: 20px;">关于ios - Swift PromiseKit : Equivalent to when() which executes sequentially?，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/48350305/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/48350305/
</a>
</p>
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