Swift 2.1 中的块存储变量

Posted 2023-02-19

【中文标题】Swift 2.1 中的块存储变量

【英文标题】：Block stored var in Swift 2.1

【发布时间】：2016-05-11 15:12:46

【问题描述】：

所以，我正在做一个异步查询，它返回多个 Worker 对象，每个 Worker 都与 WorkerPeriod 有关系，我使用这个关系来进行查询，问题是，查询是异步的，当它返回时从网络服务，workerIndex 搞砸了

 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”作为让我们在 Objective-C 中使用 __block 变量保存值的方法，但这不起作用，块交互只是忽略了值，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。

【参考方案1】：

在完成处理程序中，您需要确保workerIndex 将被捕获按值，例如：

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

见斯威夫特Capture Lists