[ios] Added action to reload style

Fixes #3102.

platform/ios/CHANGELOG.md

@@ -8,6 +8,7 @@ Mapbox welcomes participation and contributions from everyone.  If you’d like
 - Removed the `armv7s` slice from the SDK to reduce its size. iPhone 5 and iPhone 5c automatically use the `armv7` slice instead. ([#4641](https://github.com/mapbox/mapbox-gl-native/pull/4641))
 - The user dot now moves smoothly between user location updates while user location tracking is disabled. ([#1582](https://github.com/mapbox/mapbox-gl-native/pull/1582))
 - User location heading updates now resume properly when an app becomes active again. ([#4674](https://github.com/mapbox/mapbox-gl-native/pull/4674))
+- Added a `-reloadStyle:` action to MGLMapView to force a reload of the current style. ([#4728](https://github.com/mapbox/mapbox-gl-native/pull/4728))
 - A more specific user agent string is now sent with style and tile requests. ([#4012](https://github.com/mapbox/mapbox-gl-native/pull/4012))
 - Removed unused SVG files from the SDK’s resource bundle. ([#4641](https://github.com/mapbox/mapbox-gl-native/pull/4641))
 

platform/ios/include/MGLMapView.h

@@ -135,6 +135,20 @@ IB_DESIGNABLE
  */
 @property (nonatomic, null_resettable) NSURL *styleURL;
 
+/**
+ Reloads the style.
+ 
+ You do not normally need to call this method. The map view automatically
+ responds to changes in network connectivity by reloading the style. You may
+ need to call this method if you change the access token after a style has
+ loaded but before loading a style associated with a different Mapbox account.
+ 
+ This method does not bust the cache. Even if the style has recently changed on
+ the server, calling this method does not necessarily ensure that the map view
+ reflects those changes.
+ */
+- (IBAction)reloadStyle:(id)sender;
+
 /**
  A control indicating the map's direction and allowing the user to manipulate
  the direction, positioned in the upper-right corner.

platform/ios/src/MGLMapView.mm

@@ -291,6 +291,12 @@ - (void)setStyleURL:(nullable NSURL *)styleURL
     _mbglMap->setStyleURL([[styleURL absoluteString] UTF8String]);
 }
 
+- (IBAction)reloadStyle:(__unused id)sender {
+    NSURL *styleURL = self.styleURL;
+    _mbglMap->setStyleURL("");
+    self.styleURL = styleURL;
+}
+
 - (void)commonInit
 {
     _isTargetingInterfaceBuilder = NSProcessInfo.processInfo.mgl_isInterfaceBuilderDesignablesAgent;