根据要求提供 Swift "retry"逻辑

Question

所以当我的上传请求失败时，我对如何实现重试逻辑有点迷茫。

这是我的代码，我想得到一些关于如何做的指导

func startUploading(failure failure: (NSError) -> Void, success: () -> Void, progress: (Double) -> Void) {
        DDLogDebug("JogUploader: Creating jog: \(self.jog)")

        API.sharedInstance.createJog(self.jog,
            failure: { error in
                failure(error)
            }, success: {_ in
                success()
        })
    }

Answer 1

这是一个通用的解决方案，可以应用于任何没有参数的异步函数，回调函数除外。我通过只有 success 和 failure 回调简化了逻辑，progress 应该不难添加。

所以，假设你的函数是这样的:

func startUploading(success: @escaping () -> Void, failure: @escaping (Error) -> Void) {
    DDLogDebug("JogUploader: Creating jog: \(self.jog)")

    API.sharedInstance.createJog(self.jog,
        failure: { error in
            failure(error)
        }, success: {_ in
            success()
    })
}

匹配的 retry 函数可能如下所示:

func retry(times: Int, task: @escaping(@escaping () -> Void, @escaping (Error) -> Void) -> Void, success: @escaping () -> Void, failure: @escaping (Error) -> Void) {
    task(success, 
        { error in
            // do we have retries left? if yes, call retry again
            // if not, report error
            if times > 0 {
                retry(times - 1, task: task, success: success, failure: failure)
            } else {
                failure(error)
            }
        })
}

可以这样调用:

retry(times: 3, task: startUploading,
    success: {
        print("Succeeded")
    },
    failure: { err in
        print("Failed: \(err)")
})

如果一直失败，上面将重试 3 次 startUploading 调用，否则将在第一次成功时停止。

编辑。具有其他参数的函数可以简单地嵌入到闭包中:

func updateUsername(username: String, success: @escaping () -> Void, failure: @escaping (Error) -> Void) {
    ...
}

retry(times: 3, { success, failure in updateUsername(newUsername, success, failure) },
    success: {
        print("Updated username")
    },
    failure: {
        print("Failed with error: \($0)")
    }
)

---

更新 retry 函数声明中的这么多@escaping 子句可能会降低其可读性，并增加消费时的认知负担功能。为了改进这一点，我们可以编写一个具有相同功能的简单通用结构:

struct Retrier<T> {
    let times: UInt
    let task: (@escaping (T) -> Void, @escaping (Error) -> Void) -> Void
    
    func callAsFunction(success: @escaping (T) -> Void, failure: @escaping (Error) -> Void) {
        let failureWrapper: (Error) -> Void = { error in
            // do we have retries left? if yes, call retry again
            // if not, report error
            if times > 0 {
                Retrier(times: times - 1, task: task)(success: success, failure: failure)
            } else {
                failure(error)
            }
        }
        task(success, failureWrapper)
    }
    
    func callAsFunction(success: @escaping () -> Void, failure: @escaping (Error) -> Void) where T == Void {
        callAsFunction(success: { _ in }, failure: failure)
    }
}

可调用结构可以像普通函数一样被调用:

Retrier(times: 3, task: startUploading)(success: { print("success: \($0)") },
                                        failure: { print("failure: \($0)") })

，或者可以通过app传播:

let retrier = Retrier(times: 3, task: startUploading)
// ...
// sometime later
retrier(success: { print("success: \($0)") },
        failure: { print("failure: \($0)") })