wait for finished asynchronous process for getting current location in iOS app

Question

I get the current location of the iOS device in my app by using CLLocationManager and CLLocation. That works fine for me. The delivered location params latitude and longitude I want to use for another self created function. But the problem is that my function for getting the current location runs in an asynchronous process and is not finished while starting the next function.

I use delegates in my view controller for getting the current location.

Here is my code in swift:

var latitude:CLLocationDegrees = 0.0
var longitude:CLLocationDegrees = 0.0

override func viewDidLoad() {
    super.viewDidLoad()

    //get the current location and set vars latitude and logitude with right values
    self.getCurrentLocation()

    //compute distance from current location to given location
    //the result of getCurrentLocation() still not exists at this time
    //latitude and longitude still have the value 0.0 and not the real value set by getCurrentLocation()
    self.computeDistanceToGivenLocation(anotherLatitude: 10.0, anotherLogitude: 15.0)
} 

How is it possible to wait until my function getCurrentLocation() is finished before going on in the code with the next function self.computeDistanceToGivenLocation()?

Answer 1

I think you could use closures/blocks to do this. You see many of these in Cocoa frameworks with names like completionHandler.

So modify your getCurrentLocation() method in a way, that it takes an closure/block as an argument. This block contains your self.computeDistanceToGivenLocation() call. Then at the end of getCurrentLocation() you simply use the closure/block. The syntax is a bit tricky and I haven't start with swift yet. Here is the documentation.

But I'm not sure, what getCurrentLocation() actually does. Is it just telling the location manager to start updating the location? Then you should probably think about calling computeDistanceToGivenLocation() directly from the delegate method, because only this way, you can be 100% sure that the location data is there.