斯威夫特5

为了简化，创建一个“DispatchQueue+Extensions.swift”文件，内容如下:

import Foundation

typealias Dispatch = DispatchQueue

extension Dispatch {

    static func background(_ task: @escaping () -> ()) {
        Dispatch.global(qos: .background).async {
            task()
        }
    }

    static func main(_ task: @escaping () -> ()) {
        Dispatch.main.async {
            task()
        }
    }
}

用法:

Dispatch.background {
    // do stuff

    Dispatch.main { 
        // update UI
    }
}

dispatch_async(dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0), {
    // Conversion into base64 string
    self.uploadImageString =  uploadPhotoDataJPEG.base64EncodedStringWithOptions(NSDataBase64EncodingOptions.EncodingEndLineWithCarriageReturn)
})

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)
     }
}

在Swift 4.2中，这是可行的。

import Foundation

class myThread: Thread
{
    override func main() {
        while(true) {
            print("Running in the Thread");
            Thread.sleep(forTimeInterval: 4);
        }
    }
}

let t = myThread();
t.start();

while(true) {
    print("Main Loop");
    sleep(5);
}

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
})

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()
            }
        }
    }
}