如何在swift中使用背景线程？

Question

如何在swift中使用线程？

dispatchOnMainThread:^{

    NSLog(@"Block Executed On %s", dispatch_queue_get_label(dispatch_get_current_queue()));

}];

Answer 1

最佳实践是定义可多次访问的可重用函数。

e、 g.类似AppDelegate的地方。swift作为一项全球职能。

func backgroundThread(_ delay: Double = 0.0, background: (() -> Void)? = nil, completion: (() -> Void)? = nil) {
    dispatch_async(dispatch_get_global_queue(Int(QOS_CLASS_USER_INITIATED.value), 0)) {
        background?()

        let popTime = dispatch_time(DISPATCH_TIME_NOW, Int64(delay * Double(NSEC_PER_SEC)))
        dispatch_after(popTime, dispatch_get_main_queue()) {
            completion?()
        }
    }
}

注：在Swift 2.0中，替换QOS\u CLASS\u USER\u INITIATED。QOS_CLASS_USER_启动时的上述值。取而代之的是rawValue

A.在后台运行延迟3秒的进程：

    backgroundThread(3.0, background: {
            // Your background function here
    })

B、 要在后台运行进程，然后在前台运行完成：

    backgroundThread(background: {
            // Your function here to run in the background
    },
    completion: {
            // A function to run in the foreground when the background thread is complete
    })

C、 延迟3秒-注意使用不带背景参数的完成参数：

    backgroundThread(3.0, completion: {
            // Your delayed function here to be run in the foreground
    })

Answer 2

Dan Beaulieu在swift5中的回答（自swift 3.0.1起也起作用）。

extension DispatchQueue {

    static func background(delay: Double = 0.0, background: (()->Void)? = nil, completion: (() -> Void)? = nil) {
        DispatchQueue.global(qos: .background).async {
            background?()
            if let completion = completion {
                DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: {
                    completion()
                })
            }
        }
    }

}

DispatchQueue.background(delay: 3.0, background: {
    // do something in background
}, completion: {
    // when background job finishes, wait 3 seconds and do something in main thread
})

DispatchQueue.background(background: {
    // do something in background
}, completion:{
    // when background job finished, do something in main thread
})

DispatchQueue.background(delay: 3.0, completion:{
    // do something in main thread after 3 seconds
})

Answer 3

在Swift 3.0中，很多功能都得到了更新。在后台队列中运行的内容如下所示：

DispatchQueue.global(qos: .userInitiated).async {
    print("This is run on a background queue")

    DispatchQueue.main.async {
        print("This is run on the main queue, after the previous code in outer block")
    }
}

let qualityOfServiceClass = QOS_CLASS_USER_INITIATED
let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)
dispatch_async(backgroundQueue, {
    print("This is run on a background queue")

    dispatch_async(dispatch_get_main_queue(), { () -> Void in
        print("This is run on the main queue, after the previous code in outer block")
    })
})

在Swift 1.1版本中，苹果不支持上述语法，只做了一些修改。传递QOS\u CLASS\u USER\u INITIATED实际上不起作用，而是使用Int（QOS\u CLASS\u USER\u INITIATED.value）。

有关更多信息，请参阅苹果留档