问题
In Swift 2, I was able to create queue with the following code:
let concurrentQueue = dispatch_queue_create(\"com.swift3.imageQueue\", DISPATCH_QUEUE_CONCURRENT)
But this doesn\'t compile in Swift 3.
What is the preferred way to write this in Swift 3?
回答1:
Creating a concurrent queue
let concurrentQueue = DispatchQueue(label: "queuename", attributes: .concurrent)
concurrentQueue.sync {
}
Create a serial queue
let serialQueue = DispatchQueue(label: "queuename")
serialQueue.sync {
}
Get main queue asynchronously
DispatchQueue.main.async {
}
Get main queue synchronously
DispatchQueue.main.sync {
}
To get one of the background thread
DispatchQueue.global(qos: .background).async {
}
Xcode 8.2 beta 2:
To get one of the background thread
DispatchQueue.global(qos: .default).async {
}
DispatchQueue.global().async {
// qos' default value is ´DispatchQoS.QoSClass.default`
}
If you want to learn about using these queues .See this answer
回答2:
Compiles under Swift 3. This example contains most of the syntax that we need.
QoS - new quality of service syntax
weak self - to disrupt retain cycles
if self is not available, do nothing
async global background queue - for network query
async main queue - for touching the UI.
Of course, you need to add some error checking to this...
DispatchQueue.global(qos: .utility).async { [weak self] () -> Void in
guard let strongSelf = self else { return }
strongSelf.flickrPhoto.loadLargeImage { loadedFlickrPhoto, error in
if error != nil {
print("error:\(error)")
} else {
DispatchQueue.main.async { () -> Void in
activityIndicator.removeFromSuperview()
strongSelf.imageView.image = strongSelf.flickrPhoto.largeImage
}
}
}
}
回答3:
Compiled in XCode 8, Swift 3 https://github.com/rpthomas/Jedisware
@IBAction func tap(_ sender: AnyObject) {
let thisEmail = "emailaddress.com"
let thisPassword = "myPassword"
DispatchQueue.global(qos: .background).async {
// Validate user input
let result = self.validate(thisEmail, password: thisPassword)
// Go back to the main thread to update the UI
DispatchQueue.main.async {
if !result
{
self.displayFailureAlert()
}
}
}
}
回答4:
Since the OP question has already been answered above I just want to add some speed considerations:
It makes a lot of difference what priority class you assign to your async function in DispatchQueue.global.
I don't recommend running tasks with the .background thread priority especially on the iPhone X where the task seems to be allocated on the low power cores.
Here is some real data from a computationally intensive function that reads from an XML file (with buffering) and performs data interpolation:
Device name / .background / .utility / .default / .userInitiated / .userInteractive
- iPhone X: 18.7s / 6.3s / 1.8s / 1.8s / 1.8s
- iPhone 7: 4.6s / 3.1s / 3.0s / 2.8s / 2.6s
- iPhone 5s: 7.3s / 6.1s / 4.0s / 4.0s / 3.8s
Note that the data set is not the same for all devices. It's the biggest on the iPhone X and the smallest on the iPhone 5s.
回答5:
I did this and this is especially important if you want to refresh your UI to show new data without user noticing like in UITableView or UIPickerView.
DispatchQueue.main.async
{
/*Write your thread code here*/
}
回答6:
DispatchQueue.main.async {
self.collectionView?.reloadData() // Depends if you were populating a collection view or table view
}
OperationQueue.main.addOperation {
self.lblGenre.text = self.movGenre
}
//use Operation Queue if you need to populate the objects(labels, imageview, textview) on your viewcontroller
回答7:
let concurrentQueue = dispatch_queue_create("com.swift3.imageQueue", DISPATCH_QUEUE_CONCURRENT) //Swift 2 version
let concurrentQueue = DispatchQueue(label:"com.swift3.imageQueue", attributes: .concurrent) //Swift 3 version
I re-worked your code in Xcode 8, Swift 3 and the changes are marked in contrast to your Swift 2 version.
回答8:
Swift 3
you want call some closure in swift code then you want to change in storyboard ya any type off change belong to view your application will crash
but you want to use dispatch method your application will not crash
async method
DispatchQueue.main.async
{
//Write code here
}
sync method
DispatchQueue.main.sync
{
//Write code here
}
回答9:
DispatchQueue.main.async(execute: {
// write code
})
Serial Queue :
let serial = DispatchQueue(label: "Queuename")
serial.sync {
//Code Here
}
Concurrent queue :
let concurrent = DispatchQueue(label: "Queuename", attributes: .concurrent)
concurrent.sync {
//Code Here
}
回答10:
let newQueue = DispatchQueue(label: "newname")
newQueue.sync {
// your code
}
回答11:
For Swift 3
DispatchQueue.main.async {
// Write your code here
}
回答12:
Update for swift 5
Serial Queue
let serialQueue = DispatchQueue.init(label: "serialQueue")
serialQueue.async {
// code to execute
}
Concurrent Queue
let concurrentQueue = DispatchQueue.init(label: "concurrentQueue", qos: .background, attributes: .concurrent, autoreleaseFrequency: .inherit, target: nil)
concurrentQueue.async {
// code to execute
}
From Apple documentation:
Parameters
label
A string label to attach to the queue to uniquely identify it in debugging tools such as Instruments, sample, stackshots, and crash reports. Because applications, libraries, and frameworks can all create their own dispatch queues, a reverse-DNS naming style (com.example.myqueue) is recommended. This parameter is optional and can be NULL.
qos
The quality-of-service level to associate with the queue. This value determines the priority at which the system schedules tasks for execution. For a list of possible values, see DispatchQoS.QoSClass.
attributes
The attributes to associate with the queue. Include the concurrent attribute to create a dispatch queue that executes tasks concurrently. If you omit that attribute, the dispatch queue executes tasks serially.
autoreleaseFrequency
The frequency with which to autorelease objects created by the blocks that the queue schedules. For a list of possible values, see DispatchQueue.AutoreleaseFrequency.
target
The target queue on which to execute blocks. Specify DISPATCH_TARGET_QUEUE_DEFAULT if you want the system to provide a queue that is appropriate for the current object.
回答13:
it is now simply:
let serialQueue = DispatchQueue(label: "my serial queue")
the default is serial, to get concurrent, you use the optional attributes argument .concurrent
回答14:
DispatchQueue.main.async(execute: {
// code
})
回答15:
You can create dispatch queue using this code in swift 3.0
DispatchQueue.main.async
{
/*Write your code here*/
}
/* or */
let delayTime = DispatchTime.now() + Double(Int64(0.5 * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)
DispatchQueue.main.asyncAfter(deadline: delayTime)
{
/*Write your code here*/
}
来源：https://stackoverflow.com/questions/37805885/how-to-create-dispatch-queue-in-swift-3