Swift 3版本

Swift 3利用新的DispatchQueue类来管理队列和线程。要在后台线程上运行一些东西，你可以使用:

let backgroundQueue = DispatchQueue(label: "com.app.queue", qos: .background)
backgroundQueue.async {
    print("Run on background thread")
}

或者如果你想在两行代码中实现:

DispatchQueue.global(qos: .background).async {
    print("Run on background thread")

    DispatchQueue.main.async {
        print("We finished that.")
        // only back on the main thread, may you access UI:
        label.text = "Done."
    }
}

你也可以在本教程中获得一些关于Swift 3中GDC的深入信息。

Dan Beaulieu在swift5中给出了答案(从swift 3.0.1开始也可以工作)。

斯威夫特5.0.1

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()
                })
            }
        }
    }

}

使用

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
})

多用途螺纹功能

public enum QueueType {
        case Main
        case Background
        case LowPriority
        case HighPriority

        var queue: DispatchQueue {
            switch self {
            case .Main:
                return DispatchQueue.main
            case .Background:
                return DispatchQueue(label: "com.app.queue",
                                     qos: .background,
                                     target: nil)
            case .LowPriority:
                return DispatchQueue.global(qos: .userInitiated)
            case .HighPriority:
                return DispatchQueue.global(qos: .userInitiated)
            }
        }
    }

    func performOn(_ queueType: QueueType, closure: @escaping () -> Void) {
        queueType.queue.async(execute: closure)
    }

像这样使用它:

performOn(.Background) {
    //Code
}

Swift 3.0 +

在Swift 3.0中，很多东西都被现代化了。在后台队列上运行一些东西看起来像这样:

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")
    }
}

Swift 1.2到2.3

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")
    })
})

Pre Swift 1.2 -已知问题

从Swift 1.1开始，苹果在没有做一些修改的情况下不支持上述语法。传递qos_class_user_initialized实际上不起作用，而是使用Int(qos_class_user_initialized .value)。

有关更多信息，请参阅apple文档

来自Jameson Quave的教程

斯威夫特2

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
    //All stuff here
})

你必须将你想要在后台运行的更改与你想要在UI上运行的更新分开:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
    // do your task

    dispatch_async(dispatch_get_main_queue()) {
        // update some UI
    }
}