MGLMapView scaleBar position at bottom by updating constraints

Question

By default MGLMapView puts the scaleBar view at the top left of the map. I would like to move it to the bottom left, but I am having issues with doing this. Either my NSLayoutConstraint code is wrong, or something else is happening. The scaleBar is still stuck on the top left.

Here is what I have tried:

NSMutableArray *scaleBarConstraints = [[NSMutableArray alloc] init];
[self.mapboxMapView removeConstraints:self.mapboxMapView.scaleBar.constraints];
[scaleBarConstraints addObject:
 [NSLayoutConstraint constraintWithItem:self.mapboxMapView.scaleBar
                              attribute:NSLayoutAttributeBottom
                              relatedBy:NSLayoutRelationGreaterThanOrEqual
                                 toItem:self.mapboxMapView
                              attribute:NSLayoutAttributeBottom
                             multiplier:1.0
                               constant:8.0 + self.mapboxMapView.contentInset.bottom]];
[scaleBarConstraints addObject:
 [NSLayoutConstraint constraintWithItem:self.mapboxMapView.scaleBar
                              attribute:NSLayoutAttributeLeft
                              relatedBy:NSLayoutRelationEqual
                                 toItem:self.mapboxMapView
                              attribute:NSLayoutAttributeLeft
                             multiplier:1.0
                               constant:8.0 + self.mapboxMapView.contentInset.left]];

[self.mapboxMapView addConstraints:scaleBarConstraints];

Is there another way to do this or have I missed something?

Answer 1

First of all, your first constraint specifies a NSLayoutRelationGreaterThanOrEqual relation, so this means that your scaleBar's bottom edge must be somewhere above the bottom edge of the map view (+ the constant that you specified).

This is obviously true when the scale bar is positioned at the top of the map view. So try to replace NSLayoutRelationGreaterThanOrEqual with NSLayoutRelationEqual and see if it does the trick.

Warning 1:

You're adding the constraints to self.mapboxMapView which is not the direct superview of the scaleBar. (In the Mapbox library they add the constraints to a containerView.) This is bad practice. I recommend to use

[NSLayoutConstraint activateConstraints:scaleBarConstraints];

instead which will automatically add the constraints to the adequate view. (Apple recommends this in their documentation.)

Warning 2:

Generally you shouldn't hack the view hierarchy of another class (that you don't own). You cannot assume that it doesn't create new constraints at some point in time which might override or conflict with your own constraints.

Answer 2

To change scaleBar position you can mutate using scaleBarPosition property on specific place, additional you can use scaleBarMargins property for margins, for example:

scaleBarMargins = CGPoint(x: scaleBar.frame.origin.x + 'offsetX', y: scaleBar.frame.origin.y + 'offsetY')

Hope it helps!