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
    }
}

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
})

在我们的iOS应用中，中央调度是用来处理多任务的。

您可以使用此代码

// Using time interval

DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()+1) {
    print("Hello World")
}

// Background thread
queue.sync {
     for i in 0..<10 {
          print("Hello", i)
     }
}

// Main thread
for i in 20..<30 {
     print("Hello", i)
}

更多信息请访问这个链接:https://www.programminghub.us/2018/07/integrate-dispatcher-in-swift.html

我真的很喜欢Dan Beaulieu的答案，但是它在Swift 2.2中不起作用，我认为我们可以避免那些讨厌的强制打开!

func backgroundThread(delay: Double = 0.0, background: (() -> Void)? = nil, completion: (() -> Void)? = nil) {

    dispatch_async(dispatch_get_global_queue(QOS_CLASS_USER_INITIATED, 0)) {

        background?()

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

快4.倍

把这些放到文件中:

func background(work: @escaping () -> ()) {
    DispatchQueue.global(qos: .userInitiated).async {
        work()
    }
}

func main(work: @escaping () -> ()) {
    DispatchQueue.main.async {
        work()
    }
}

然后在需要的地方调用它:

background {
     //background job
     main {
       //update UI (or what you need to do in main thread)
     }
}