如何在Swift中初始化MapView

Question

Goal:

1. I have a class that declares a map view and finds the user's current location. This class is called MapController() .
2. I have another class that needs to call MapController() , and drop a pin at the user's current location.

Problem:

While I'm in the other class and trying to call MapController() , MapController() 's MapView never gets initialized.

Solution I need:

How do I initialize a MapView?

Answer 1

A number of times you are referencing:

let map = MapController().mapView

That isn't doing what you think it does:

• Rather than referencing a map on an existing view controller, MapController() is instantiating a brand new view controller. But since you don't do anything with that view controller, but rather just let it fall out of scope, it is immediately deallocated.

• Even if you didn't let it fall out of scope (eg you transitioned to it somehow), you're not instantiating that through the storyboard, so the outlets will be nil . If you were really trying to instantiate a new instance of MapController , you'd do something like:

   let controller = storyboard?.instantiateViewControllerWithIdentifier("MapControllerScene") 

• Frankly, even if you solved the above issues, one view controller has no business interacting directly with the MKMapView of another view controller scene.

So, the question is what is the correct way to achieve what you intended.

There are three basic techniques:

1. Keep the "add note" and the map view loosely coupled and have Note Detail View Controller simply post a notification to NSNotificationCenter.defaultCenter() and then have the map view observe that custom notification.

2. Navigate through the view controller hierarchy to get to the map view controller (eg the second child of the navigation bar's tab controller). Or actively pass the map view controller reference as a parameter that you pass from view controller to view controller. Anyway, if you had a reference to the existing map view controller, you can now pass data back directly. You might want to implement a protocol to avoid tight coupling of these two classes.

3. Perform some unwind segue to navigate back from note detail view controller back to the map view and then use prepareForSegue to pass the data back. In iOS 9 you no longer have to unwind solely to a class higher in the view controller hierarchy, though that makes life a little easier for you if you do that.