如何在swift中使用后台线程？

本文翻译自：How to use background thread in swift?

How to use threading in swift? 如何在swift中使用线程？

dispatchOnMainThread:^{

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

}];

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#1楼

参考：https://stackoom.com/question/1cw7J/如何在swift中使用后台线程

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#2楼

From Jameson Quave's tutorial 来自Jameson Quave的教程

Swift 2 斯威夫特2

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

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#3楼

Swift 3.0+ Swift 3.0+

A lot has been modernized in Swift 3.0. 很多已经在Swift 3.0中进行了现代化改造 。 Running something on the background thread looks like this: 在后台线程上运行一些东西看起来像这样：

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

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

Swift 1.2 through 2.3 Swift 1.2到2.3

let qualityOfServiceClass = QOS_CLASS_BACKGROUND
let backgroundQueue = dispatch_get_global_queue(qualityOfServiceClass, 0)
dispatch_async(backgroundQueue, {
    print("This is run on the 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 – Known issue Pre Swift 1.2 - 已知问题

As of Swift 1.1 Apple didn't support the above syntax without some modifications. 从Swift 1.1开始，如果没有一些修改，Apple不支持上述语法。 Passing QOS_CLASS_BACKGROUND didn't actually work, instead use Int(QOS_CLASS_BACKGROUND.value) . 传递QOS_CLASS_BACKGROUND实际上并不起作用，而是使用Int(QOS_CLASS_BACKGROUND.value) 。

For more information see Apples documentation 有关更多信息，请参阅Apples文档

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#4楼

The best practice is to define a reusable function that can be accessed multiple times. 最佳实践是定义可以多次访问的可重用函数。

REUSABLE FUNCTION: 可重复使用的功能：

eg somewhere like AppDelegate.swift as a Global Function. 例如AppDelegate.swift作为全局函数。

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?()
        }
    }
}

Note: in Swift 2.0, replace QOS_CLASS_USER_INITIATED.value above with QOS_CLASS_USER_INITIATED.rawValue instead 注意：在Swift 2.0中，用QOS_CLASS_USER_INITIATED.rawValue替换上面的QOS_CLASS_USER_INITIATED.value

USAGE: 用法：

A. To run a process in the background with a delay of 3 seconds: A.要在后台运行一个延迟3秒的进程：

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

B. To run a process in the background then run a completion in the foreground: B.要在后台运行进程，请在前台运行完成：

    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. To delay by 3 seconds - note use of completion parameter without background parameter: C.延迟3秒 - 注意使用没有背景参数的完成参数：

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

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#5楼

You have to separate out the changes that you want to run in the background from the updates you want to run on the UI: 您必须从要在UI上运行的更新中分离出要在后台运行的更改：

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

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

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#6楼

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