GCD in Swfit 3.0

主要是嘚瑟一下英文。其实代码都在，什么文都无所谓。代码在这里：https://github.com/future-challenger/Swift3.0/tree/master/GCD

This project is “forked” from raywenderlich GCD tutorial. It’s really a good tutorial where I learned what I wanted. But it’s kinda out of date. In Swift 3.0,lots of API in iOS SDK have been modified. Including how GCD APIs are called. So I update the tutorial to swift 3.0

Main Queue

dispatch_get_main_queue => DispatchQueue.main

Global Queue

dispatch_get_global_queue => DispatchQueue.global(qos:)
before:

dispatch_get_global_queue(Int(QOS_CLASS_USER_INTERACTIVE.value),0)

Swift 3.0

DispatchQueue.global(qos: .userInteractive)

Here’s a easy one. Before we always do things like this:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH,0),^{
    // do something background
    dispatch_async(dispatch_get_main_queue(),^{
        // update UI in main thread(or UI thread)
    });
});

In swift 3.0,we do it this way.

DispatchQueue.global(qos: .userInitiated).async {
    // background things
    DispatchQueue.main.async {
        print("main thread dispatch")
    }
}

Dispatch After & Once

Dispatch After

before you do dispatch after like this:

var dispatchTime: dispatch_time_t = dispatch_time(DISPATCH_TIME_NOW,Int64(0.1 * Double(NSEC_PER_SEC)))
dispatch_after(dispatchTime,dispatch_get_main_queue(),{
    // your function here
})

In swift 3.0

let dispatchTime: DispatchTime = DispatchTime.now() + Double(Int64(0.1 * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)
DispatchQueue.main.asyncAfter(deadline: dispatchTime,execute: {
    // your function here
})

or even more simply:

DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
    // your function here
}

Disaptch Once

This dispatch_once on longer exists in Swift 3.0.

According to Apple’s migration guide:

The free function dispatch_once is no longer available in Swift. In Swift,you can use lazily initialized globals or static properties and get the same thread-safety and called-once guarantees as dispatch_once provided.

You can use lazy initialized global or static properties instead of dispatch once. eg:

// global constant: SomeClass initializer gets called lazily,only on first use
let foo = SomeClass()

// global var,same thing happens here
// even though the "initializer" is an immediately invoked closure
var bar: SomeClass = {
    let b = SomeClass()
    b.someProperty = "whatever"
    b.doSomeStuff()
    return b
}()

// ditto for static properties in classes/structures/enums
class MyClass {
    static let singleton = MyClass()
    init() {
        print("foo")
    }
}

reference:
http://stackoverflow.com/questions/37801407/whither-dispatch-once-in-swift-3
http://stackoverflow.com/questions/37801436/how-do-i-write-dispatch-after-gcd-in-swift-3