Pause rendering when entering background

CHANGELOG.md

@@ -6,6 +6,7 @@ Mapbox welcomes participation and contributions from everyone.
 
 * Updated to MapboxCoreMaps 10.3.0 and MapboxCommon 21.1.0. ([#1078](https://github.com/mapbox/mapbox-maps-ios/pull/1078))
 * Fix compass button regression introduced in rc.1. ([#1083](https://github.com/mapbox/mapbox-maps-ios/pull/1083))
+* Prevent rendering in background by pausing/resuming display link in response to application or scene lifecycle events ([#1086](https://github.com/mapbox/mapbox-maps-ios/pull/1086))
 
 ## 10.3.0-rc.1 – January 26, 2022
 

Sources/MapboxMaps/Foundation/DisplayLinkProtocol.swift

@@ -10,6 +10,7 @@ internal protocol DisplayLinkProtocol: AnyObject {
     @available(iOS 15.0, *)
     var preferredFrameRateRange: CAFrameRateRange { get set }
     #endif
+    var isPaused: Bool { get set }
     func add(to runloop: RunLoop, forMode mode: RunLoop.Mode)
     func invalidate()
 }

Sources/MapboxMaps/Foundation/Extensions/UIWindow.swift

@@ -0,0 +1,16 @@
+import UIKit
+
+@available(iOS 13.0, *)
+extension UIWindow {
+    private static let templateApplicationSceneSelector = Selector(("templateApplicationScene"))
+
+    internal var parentScene: UIScene? {
+        var carPlayScene: UIScene? {
+            guard self.responds(to: UIWindow.templateApplicationSceneSelector) else {
+                return nil
+            }
+            return self.value(forKey: UIWindow.templateApplicationSceneSelector.description) as? UIScene
+        }
+        return windowScene ?? carPlayScene
+    }
+}

Sources/MapboxMaps/Foundation/MapView+Lifecycle.swift

@@ -0,0 +1,89 @@
+import Foundation
+import UIKit
+
+@available(iOSApplicationExtension, unavailable)
+extension MapView {
+    private static let UIApplicationSceneManifestKey = "UIApplicationSceneManifest"
+
+    internal func subscribeToMemoryWarningNotification() {
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(didReceiveMemoryWarning),
+                                               name: UIApplication.didReceiveMemoryWarningNotification,
+                                               object: nil)
+    }
+
+    internal func subscribeToLifecycleNotifications() {
+        if Bundle.main.object(forInfoDictionaryKey: MapView.UIApplicationSceneManifestKey) != nil {
+            if #available(iOS 13.0, *) {
+                subscribeToSceneLifecycleNotifications()
+            }
+        } else {
+            subscribeToApplicationsLifecycleNotifications()
+        }
+    }
+
+    internal func unsubscribeFromLifecycleNotifications() {
+        if Bundle.main.object(forInfoDictionaryKey: MapView.UIApplicationSceneManifestKey) != nil {
+            if #available(iOS 13.0, *) {
+                NotificationCenter.default.removeObserver(self, name: UIScene.willEnterForegroundNotification, object: nil)
+                NotificationCenter.default.removeObserver(self, name: UIScene.didEnterBackgroundNotification, object: nil)
+            }
+        } else {
+            NotificationCenter.default.removeObserver(self, name: UIApplication.willEnterForegroundNotification, object: nil)
+            NotificationCenter.default.removeObserver(self, name: UIApplication.didEnterBackgroundNotification, object: nil)
+        }
+    }
+
+    @objc internal func didReceiveMemoryWarning() {
+        mapboxMap.reduceMemoryUse()
+    }
+
+    @objc internal func willEnterForeground() {
+        resumeDisplayLink()
+    }
+
+    @objc internal func didEnterBackground() {
+        mapboxMap.reduceMemoryUse()
+        pauseDisplayLink()
+    }
+
+    @available(iOS 13.0, *)
+    @objc private func didReceiveSceneLifecycleNotification(_ notification: Notification) {
+        // making sure the scene is the correct one, as the scene may not be available when subscribing
+        guard let scene = notification.object as? UIScene, scene == window?.parentScene else {
+            return
+        }
+
+        switch notification.name {
+        case UIScene.willEnterForegroundNotification:
+            willEnterForeground()
+        case UIScene.didEnterBackgroundNotification:
+            didEnterBackground()
+        default:
+            break
+        }
+    }
+
+    @available(iOS 13.0, *)
+    private func subscribeToSceneLifecycleNotifications() {
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(willEnterForeground),
+                                               name: UIScene.willEnterForegroundNotification,
+                                               object: window?.parentScene)
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(didEnterBackground),
+                                               name: UIScene.didEnterBackgroundNotification,
+                                               object: window?.parentScene)
+    }
+
+    private func subscribeToApplicationsLifecycleNotifications() {
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(willEnterForeground),
+                                               name: UIApplication.willEnterForegroundNotification,
+                                               object: nil)
+        NotificationCenter.default.addObserver(self,
+                                               selector: #selector(didEnterBackground),
+                                               name: UIApplication.didEnterBackgroundNotification,
+                                               object: nil)
+    }
+}

Sources/MapboxMaps/Foundation/MapView.swift

@@ -232,11 +232,6 @@ open class MapView: UIView {
         mapClient.delegate = self
         mapboxMap = MapboxMap(mapClient: mapClient, mapInitOptions: resolvedMapInitOptions)
 
-        NotificationCenter.default.addObserver(self,
-                                               selector: #selector(didReceiveMemoryWarning),
-                                               name: UIApplication.didReceiveMemoryWarningNotification,
-                                               object: nil)
-
         // Use the overriding style URI if provided (currently from IB)
         if let initialStyleURI = overridingStyleURI,
            let styleURI = StyleURI(url: initialStyleURI) {
@@ -274,6 +269,8 @@ open class MapView: UIView {
 
         // Set up managers
         setupManagers()
+
+        subscribeToMemoryWarningNotification()
     }
 
     internal func setupManagers() {
@@ -430,7 +427,9 @@ open class MapView: UIView {
 
         if window != nil {
             validateDisplayLink()
+            subscribeToLifecycleNotifications()
         } else {
+            unsubscribeFromLifecycleNotifications()
             // TODO: Fix this up correctly.
             displayLink?.invalidate()
             displayLink = nil
@@ -442,8 +441,12 @@ open class MapView: UIView {
         super.didMoveToSuperview()
     }
 
-    @objc func didReceiveMemoryWarning() {
-        mapboxMap.reduceMemoryUse()
+    internal func resumeDisplayLink() {
+        displayLink?.isPaused = false
+    }
+
+    internal func pauseDisplayLink() {
+        displayLink?.isPaused = true
     }
 
     // MARK: Location

Tests/MapboxMapsTests/Foundation/MapViewTests.swift

@@ -187,4 +187,15 @@ final class MapViewTests: XCTestCase {
         mapView.didReceiveMemoryWarning()
     }
 
+    func testWillEnterForeground() {
+        mapView.willEnterForeground()
+
+        XCTAssertFalse(displayLink.isPaused)
+    }
+
+    func testDidEnterBackground() {
+        mapView.didEnterBackground()
+
+        XCTAssertTrue(displayLink.isPaused)
+    }
 }

Tests/MapboxMapsTests/Foundation/Mocks/MockDisplayLink.swift

@@ -9,6 +9,8 @@ final class MockDisplayLink: DisplayLinkProtocol {
 
     var preferredFramesPerSecond: Int = 0
 
+    var isPaused: Bool = false
+
     // Checking Swift version as a proxy for iOS SDK version to enable
     // building with iOS SDKs < 15
     #if swift(>=5.5)