Issue while calling mutlile API in swift 3? - ios

Question

I have two classes.Class A and Class B. In class A there is table view.When i tap on cell in class A i call first api to save the data /saveData & on response of first api i call another api getData.I call these API in background.Now when i move to class A i call the another API on viewDidLoad().I call this in foreground .Now i want that the API of class A should not effect the class B.
Please tell what is the best way to do that.
i tried DispatchGroup but did not work for me.
func saveInBackground(parameter : [String : AnyObject]?) -> Void {
let group = DispatchGroup()
group.notify(queue: DispatchQueue.global(qos: .background)){
let apiManager = APIHandler(baseURL: Constants.API.baseURL, APIVersion: "")
apiManager.requestOfBgMethod(.post, path: Constants.API.Name.addGeneralField.completePath, parameters: parameter, encoding: .url, headers: nil, apiSuccess: { (result) in
//update user
self.copyUser = User(copyFrom: self.user)
self.saveCVResponse(result: result)
//fetch data in background
Utility.sharedInstance.updateCVdata(cvManager: self.cvManager)
}, apiFailure: { (error) in
})
}
// DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async {
//
//
// }
}

Answer 1

Use DispatchSemaphore and a Singleton instance to make API calling one by one:
class ApiHelper {
static let shardInstance = ApiHelper()
private let semaphore = DispatchSemaphore(value: 1) //one task allowed at a time
private let apiManager = APIHandler(baseURL: Constants.API.baseURL, APIVersion: "")
func saveInBackground(parameter : [String : AnyObject]?) -> Void {
DispatchQueue.global(qos: .default).async { [unowned self] in
self.semaphore.wait() //lock
apiManager.requestOfBgMethod(.post, path: Constants.API.Name.addGeneralField.completePath, parameters: parameter, encoding: .url, headers: nil, apiSuccess: { (result) in
//.......
self.semaphore.signal() //unlock
}, apiFailure: { (error) in
self.semaphore.signal() //unlock
})
}
}
}
Use it in Class A and Class B, they will not be effected each other:
ApiHelper.shardInstance.saveInBackground(parameter: nil)

Answer 2

Use global DispatchSemaphore without Singleton:
In class A or class B or somewhere, define a global semaphore out of class:
let semaphoreGlobal = DispatchSemaphore(value: 1) //one task at a time
//ignore following, just an example.
class AnyClass {
//......
}
And your method become:
func saveInBackground(parameter : [String : AnyObject]?) -> Void {
DispatchQueue.global(qos: .default).async {
semaphoreGlobal.wait() //wait if semaphore is 0. Else, set semaphore to 0 and continue.
//remember: the variable 'apiManager' should not be a local one.
apiManager.requestOfBgMethod(.post, path: Constants.API.Name.addGeneralField.completePath, parameters: parameter, encoding: .url, headers: nil, apiSuccess: { (result) in
//.......
semaphoreGlobal.signal() //set semaphore to 1, means allowing one of other tasks stops waiting.
}, apiFailure: { (error) in
semaphoreGlobal.signal() //set semaphore to 1
})
}
}