Adding buttons to toolbar programmatically in swift

The usual way to do that is to create the array of toolbar items and then assign the array to the items property of the toolbar.

self.navigationController?.isToolbarHidden = false
var items = [UIBarButtonItem]()
items.append(
    UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
)
items.append(
    UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(onClickedToolbeltButton(_:)))
)
toolbarItems = items

Here is an example with MKUserTrackingBarButtonItem:

navigationController?.toolbarHidden = false
let barButtonItem = MKUserTrackingBarButtonItem(mapView: self.mapView)
self.toolbarItems = [barButtonItem]

None of the above worked for me, but:

Swift 3 / Swift 4

self.navigationController?.isToolbarHidden = false

var items = [UIBarButtonItem]()

items.append( UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: self, action: nil) )
items.append( UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(add)) ) // replace add with your function

self.toolbarItems = items // this made the difference. setting the items to the controller, not the navigationcontroller

self.navigationController?.toolbarItems = items

self.navigationController?.setToolbarItems(items, animated: false)

self.navigationController?.toolbar.setItems(items, animated: false)

Try it.

        self.navigationController?.toolbarHidden = false
        var items = [UIBarButtonItem]()
        items.append(
            UIBarButtonItem(barButtonSystemItem: .FlexibleSpace, target: self, action: nil)
        )
        items.append(
            UIBarButtonItem(barButtonSystemItem: .Add, target: self, action: "onClickedToolbeltButton:")
        )

        self.navigationController?.toolbar.setItems(items, animated: false)