Merge pull request #75 from hyperoslo/fix/crash

Check parent before adding constraints

Author: onmyway133

Example/GalleryDemo/GalleryDemo/Sources/AppDelegate.swift

@@ -9,12 +9,12 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
   lazy var navigationController: UINavigationController = { [unowned self] in
     let controller = UINavigationController(rootViewController: self.viewController)
     return controller
-    }()
+  }()
 
   lazy var viewController: ViewController = {
     let controller = ViewController()
     return controller
-    }()
+  }()
 
   func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
     window = UIWindow(frame: UIScreen.main.bounds)

Sources/Utils/Pages/PagesController.swift

@@ -89,25 +89,25 @@ class PagesController: UIViewController {
     let usePageIndicator = controllers.count > 1
     if usePageIndicator {
       view.addSubview(pageIndicator)
-    }
-    view.addSubview(scrollView)
-    scrollView.addSubview(scrollViewContentView)
-
-    Constraint.on(
-      pageIndicator.leftAnchor.constraint(equalTo: pageIndicator.superview!.leftAnchor),
-      pageIndicator.rightAnchor.constraint(equalTo: pageIndicator.superview!.rightAnchor),
-      pageIndicator.heightAnchor.constraint(equalToConstant: 40)
-    )
-
-    if #available(iOS 11, *) {
-      Constraint.on(
-        pageIndicator.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor)
-      )
-    } else {
       Constraint.on(
-        pageIndicator.bottomAnchor.constraint(equalTo: pageIndicator.superview!.bottomAnchor)
+        pageIndicator.leftAnchor.constraint(equalTo: pageIndicator.superview!.leftAnchor),
+        pageIndicator.rightAnchor.constraint(equalTo: pageIndicator.superview!.rightAnchor),
+        pageIndicator.heightAnchor.constraint(equalToConstant: 40)
       )
+      
+      if #available(iOS 11, *) {
+        Constraint.on(
+          pageIndicator.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor)
+        )
+      } else {
+        Constraint.on(
+          pageIndicator.bottomAnchor.constraint(equalTo: pageIndicator.superview!.bottomAnchor)
+        )
+      }
     }
+    
+    view.addSubview(scrollView)
+    scrollView.addSubview(scrollViewContentView)
 
     scrollView.g_pinUpward()
     if usePageIndicator {