swift - 在 Swift 2.1 中阻止存储的变量

Question

所以，我正在做一个返回多个 Worker 对象的异步查询，每个 Worker 都与 WorkerPeriod 有关系，我使用这个关系来做查询，问题是，查询是异步的，当它返回时从 Web 服务，workerIndex 乱七八糟

 workerQuery.whereKey("construction", equalTo: currentConstruction).findObjectsInBackgroundWithBlock({ (unsafeWorkers, error) -> Void in
            guard let workers = unsafeWorkers as? [Worker] where error == nil && workers.count == 0 else {
                return
            }

            for var workerIndex = 0; workerIndex < workers.count; workerIndex++ {

                let currentWorker = workers[workerIndex]


                if let periodQuery = WorkerPeriod.query() {
                    periodQuery.whereKey("worker", equalTo: currentWorker)

                    let weakWorkerIndex = workerIndex
                    print("weakWorkerIndex = \(weakWorkerIndex) worker \(workerIndex)")
                    periodQuery.findObjectsInBackgroundWithBlock({ (unsafeWorkerPeriod, error) -> Void in

                        guard let workerPeriods = unsafeWorkerPeriod as? [WorkerPeriod] where error == nil && workerPeriods.count != 0 else {
                            return
                        }
                        print("block weakWorkerIndex = \(weakWorkerIndex) workerIndex \(workerIndex)")

                        .
                        .

                    })
                }
            }

我尝试创建一个“weakWorkerIndex”作为 let 来保存值，就像我们在 Objective-C 中使用 __block 变量所做的那样，但这不起作用， block 交互只是忽略了值，如您所见在输出中:

weakWorkerIndex = 0 worker 0
weakWorkerIndex = 1 worker 1
block weakWorkerIndex = 0 workerIndex 2
block weakWorkerIndex = 0 workerIndex 2
block weakWorkerIndex = 0 workerIndex 2

顺便说一句:我删除了所有不必要的代码以简化阅读。

Answer 1

在完成处理程序中，您需要确保workerIndex 将被按值 捕获，例如:

for var workerIndex = 0; workerIndex < 10; workerIndex++ {
    fooAsync { [workerIndex] in
        print("\(workerIndex)")
    }
}

参见 Swift Capture Lists