如何运行在后台编码？使用 dispatch_async 它是如何工作的？

Question

我是 Swift.I 的新手，我有以下完美运行的代码。即我正在从电话簿中获取联系人并成功更新到 sqlite。

我的要求

我想运行在后台编码，即在我下面的代码中，我正在做的是每当电话簿中的某些联系人 added/deleted 我正在更新 sqlite。我一直想要这个功能。它应该总是运行在后台。

这是我的代码

func getContactNames()
{
    if !self.determineStatus()
    {
        print("not authorized")
        return
    }

    let contactList: NSArray = ABAddressBookCopyArrayOfAllPeople(adbk).takeRetainedValue()
    print("records in the array \(contactList.count)")


    var firstName : String = String()

    var contactNumber : String = String()


    var lastName : String = String()


    var email : String = String()


    var fullName : String = String()


    let db = ContactsDBModel.sharedInstance()


    var  contacts : [ContactsModel!]?


    contacts =  db.selectAllFromContact()

    print(contacts?.count)

    if contacts?.count != contactList.count
    {

        db.deleteAllFromContact()

        for record:ABRecordRef in contactList
        {
            if (ABRecordCopyValue(record,
                kABPersonPhoneProperty) != nil)

            {


                if (ABRecordCopyValue(record,
                    kABPersonFirstNameProperty) != nil)

                {


                    firstName = (ABRecordCopyValue(record, kABPersonFirstNameProperty)?.takeRetainedValue() as? String)!

                    let numbers:ABMultiValue = ABRecordCopyValue(record, kABPersonPhoneProperty).takeRetainedValue()


                    contactNumber = (ABMultiValueCopyValueAtIndex(numbers,0)?.takeRetainedValue() as? String)!
                    // print("first name =\(firstName)")

                   // print("contact number=\(contactNumber)")

                    if (ABRecordCopyValue(record,
                        kABPersonLastNameProperty) != nil)
                    {

                       lastName = (ABRecordCopyValue(record,
                            kABPersonLastNameProperty).takeRetainedValue()as? String)!
                       // print("last name =\(lastName)")
                    }


                    let emails: ABMultiValueRef = ABRecordCopyValue(record, kABPersonEmailProperty).takeRetainedValue()

                    for (var i = 0; i < ABMultiValueGetCount(emails); i++)
                    {
                        email = ABMultiValueCopyValueAtIndex(emails, i).takeRetainedValue() as! String
                      //  print("email of person=\(email)")
                    }

                }

            }

            fullName = firstName + lastName;
            lastName = "";

            print("fullName of person=\(fullName)")
            print("email of person=\(email)")
            print("contact number=\(contactNumber)")


            db.insertIntoContact(contactNumber: contactNumber, contactName: fullName, contactEmail: email)


        }

        contacts =  db.selectAllFromContact()

        print(contacts?.count)

  }


    print(contacts?.count)


}

上面的代码我想运行在后台。

更新

viewDidLoad

override func viewDidLoad()
{
    super.viewDidLoad()
    var emptyDictionary: CFDictionaryRef?
    var addressBook: ABAddressBookRef?

            func extractABAddressBookRef(abRef: Unmanaged<ABAddressBookRef>!) -> ABAddressBookRef?
            {
                if let ab = abRef
                {
                    return Unmanaged<NSObject>.fromOpaque(ab.toOpaque()).takeUnretainedValue()
                }
                return nil
            }

            if (ABAddressBookGetAuthorizationStatus() == ABAuthorizationStatus.NotDetermined)
            {
                print("requesting access...")
                var errorRef: Unmanaged<CFError>? = nil
                addressBook = extractABAddressBookRef(ABAddressBookCreateWithOptions(nil, &errorRef))
                ABAddressBookRequestAccessWithCompletion(addressBook, { success, error in
                    if success {
                        self.getContactNames()
                    }
                    else
                    {
                        print("error")
                    }
                })
            }
            else if (ABAddressBookGetAuthorizationStatus() == ABAuthorizationStatus.Denied || ABAddressBookGetAuthorizationStatus() == ABAuthorizationStatus.Restricted)
            {
            print("access denied")
            }
            else if (ABAddressBookGetAuthorizationStatus() == ABAuthorizationStatus.Authorized)
            {
            print("access granted")
            getContactNames()
            }


   }

dispatch_async

 dispatch_async(dispatch_get_global_queue(   DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){
//Background Thread
 dispatch_async(dispatch_get_main_queue(), ^(void){
    //Run UI Updates
    });
 });

我听说使用 dispatch_async 我们可以运行代码 background.But 把我上面的代码放在哪里？有哪些场景？

Answer 1

我们可以用dispatch_async来做。
例如，这是下载一些图像并存储在后台的 UserDefaults 中

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { () -> Void in
                let imageData = NSData(contentsOfURL: NSURL(string: thankYouImageURL)!)
                if let data = imageData {
                    print("Success Thanks Image")
                    NSUserDefaults.standardUserDefaults().setObject(data, forKey: "registerThanksImage")

                }else{
                    print("failure thanks image")
                }

            }

一般语法

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
        // do background task
        dispatch_async(dispatch_get_main_queue()) {
            // update some UI
        }
    }

Answer 2

Grand Central Dispatch 中的异步调度在 Swift 中有语法糖。您可以在这里找到它：https://github.com/duemunk/Async

在后台运行您的代码非常容易。

就像这样：

Async.background {
     println("This is run on the background queue")
}.main {
     println("This is run on the main queue, after the previous block")
}

如何运行在后台编码？使用 dispatch_async 它是如何工作的？

How to run code in background ? using dispatch_async how it works?

sqlite

abaddressbook

ios

dispatch-async

swift

如何 运行 在后台编码？使用 dispatch_async 它是如何工作的？

How to run code in background ? using dispatch_async how it works?

sqlite

abaddressbook

ios

dispatch-async

swift

如何运行在后台编码？使用 dispatch_async 它是如何工作的？