[ios] Add MGLMapView.showsScale to control scale bar visibility

- Fixes scale bar not being visible until a camera change event.
- Adds IBInspectable for scale bar visibility.

platform/ios/CHANGELOG.md

@@ -49,6 +49,8 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 * Long-pressing the attribution button causes the SDK’s version number to be displayed in the action sheet that appears. ([#10650](https://github.com/mapbox/mapbox-gl-native/pull/10650))
 * Reduced offline download size for styles with symbol layers that render only icons, and no text. ([#11055](https://github.com/mapbox/mapbox-gl-native/pull/11055))
 * Added haptic feedback that occurs when the user rotates the map to due north, configurable via `MGLMapView.hapticFeedbackEnabled`. ([#10847](https://github.com/mapbox/mapbox-gl-native/pull/10847))
+* Added `MGLMapView.showsScale` as the recommended way to show the scale bar. This property can be set directly in Interface Builder. ([#11335](https://github.com/mapbox/mapbox-gl-native/pull/11335))
+* Fixed an issue where the scale bar would not appear until the map had moved. ([#11335](https://github.com/mapbox/mapbox-gl-native/pull/11335))
 
 ## 3.7.5 - February 16, 2018
 

platform/ios/app/MBXViewController.m

@@ -164,7 +164,7 @@ - (void)viewDidLoad
     [self restoreState:nil];
 
     self.debugLoggingEnabled = [[NSUserDefaults standardUserDefaults] boolForKey:@"MGLMapboxMetricsDebugLoggingEnabled"];
-    self.mapView.scaleBar.hidden = NO;
+    self.mapView.showsScale = YES;
     self.mapView.showsUserHeadingIndicator = YES;
     if ([UIFont respondsToSelector:@selector(monospacedDigitSystemFontOfSize:weight:)]) {
         self.hudLabel.titleLabel.font = [UIFont monospacedDigitSystemFontOfSize:10 weight:UIFontWeightRegular];

platform/ios/src/MGLMapView+IBAdditions.h

@@ -44,6 +44,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic) IBInspectable BOOL allowsTilting;
 @property (nonatomic) IBInspectable BOOL showsUserLocation;
 @property (nonatomic) IBInspectable BOOL showsHeading;
+@property (nonatomic) IBInspectable BOOL showsScale;
 
 @end
 

platform/ios/src/MGLMapView.h

@@ -220,9 +220,18 @@ MGL_EXPORT IB_DESIGNABLE
  */
 - (IBAction)reloadStyle:(id)sender;
 
+/**
+ A Boolean value indicating whether the map may display scale information.
+
+ The scale bar may not be shown at all zoom levels. The view controlled by this
+ property is available at `scaleBar`. The default value of this property is
+ `NO`.
+ */
+@property (nonatomic, assign) BOOL showsScale;
+
 /**
  A control indicating the scale of the map. The scale bar is positioned in the
- upper-left corner. The scale bar is hidden by default.
+ upper-left corner. Enable the scale bar via `showsScale`.
  */
 @property (nonatomic, readonly) UIView *scaleBar;
 

platform/ios/src/MGLMapView.mm

@@ -975,8 +975,8 @@ - (void)glkView:(__unused GLKView *)view drawInRect:(__unused CGRect)rect
 - (void)layoutSubviews
 {
     // Calling this here instead of in the scale bar itself because if this is done in the
-    // scale bar instance, it triggers a call to this this `layoutSubviews` method that
-    // calls `_mbglMap->setSize()` just below that triggers rendering update which triggers
+    // scale bar instance, it triggers a call to this `layoutSubviews` method that calls
+    // `_mbglMap->setSize()` just below that triggers rendering update which triggers
     // another scale bar update which causes a rendering update loop and a major performace
     // degradation. The only time the scale bar's intrinsic content size _must_ invalidated
     // is here as a reaction to this object's view dimension changes.
@@ -2362,6 +2362,17 @@ - (void)setPitchEnabled:(BOOL)pitchEnabled
     self.twoFingerDrag.enabled = pitchEnabled;
 }
 
+- (void)setShowsScale:(BOOL)showsScale
+{
+    _showsScale = showsScale;
+    self.scaleBar.hidden = !showsScale;
+
+    if (showsScale)
+    {
+        [self updateScaleBar];
+    }
+}
+
 #pragma mark - Accessibility -
 
 - (NSString *)accessibilityValue
@@ -5413,10 +5424,7 @@ - (void)cameraIsChanging {
     }
 
     [self updateCompass];
-
-    if (!self.scaleBar.hidden) {
-        [(MGLScaleBar *)self.scaleBar setMetersPerPoint:[self metersPerPointAtLatitude:self.centerCoordinate.latitude]];
-    }
+    [self updateScaleBar];
 
     if ([self.delegate respondsToSelector:@selector(mapView:regionIsChangingWithReason:)])
     {
@@ -5434,6 +5442,7 @@ - (void)cameraDidChangeAnimated:(BOOL)animated {
     }
 
     [self updateCompass];
+    [self updateScaleBar];
 
     if ( ! [self isSuppressingChangeDelimiters])
     {
@@ -5878,6 +5887,17 @@ - (void)updateCompass
     }
 }
 
+- (void)updateScaleBar
+{
+    // Use the `hidden` property (instead of `self.showsScale`) so that we don't
+    // break developers who still rely on the <4.0.0 approach of directly
+    // setting this property.
+    if ( ! self.scaleBar.hidden)
+    {
+        [(MGLScaleBar *)self.scaleBar setMetersPerPoint:[self metersPerPointAtLatitude:self.centerCoordinate.latitude]];
+    }
+}
+
 + (UIImage *)resourceImageNamed:(NSString *)imageName
 {
     UIImage *image = [UIImage imageNamed:imageName