From 46691a60e8ac31348dea65b9770a0df3fe577649 Mon Sep 17 00:00:00 2001
From: svsk417 <svoskuhl@slashwhy.de>
Date: Mon, 7 Mar 2022 19:08:33 +0100
Subject: [PATCH] resolves #486

---
 package/lib/src/beamer.dart          | 17 +++++++++++++----
 package/lib/src/beamer_delegate.dart | 10 ++++++++--
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/package/lib/src/beamer.dart b/package/lib/src/beamer.dart
index e4c6670b..ac99ac26 100644
--- a/package/lib/src/beamer.dart
+++ b/package/lib/src/beamer.dart
@@ -57,7 +57,7 @@ class Beamer extends StatefulWidget {
 /// A [State] for [Beamer].
 class BeamerState extends State<Beamer> {
   /// A parent Router of this Beamer / Router.
-  late Router parent;
+  late Router? parent;
 
   /// A getter for [BeamerDelegate] of the [Beamer] whose state is this.
   BeamerDelegate get routerDelegate => widget.routerDelegate;
@@ -69,17 +69,26 @@ class BeamerState extends State<Beamer> {
   void didChangeDependencies() {
     super.didChangeDependencies();
     parent = Router.of(context);
-    routerDelegate.parent = parent.routerDelegate as BeamerDelegate;
+    routerDelegate.parent = parent!.routerDelegate as BeamerDelegate;
+  }
+  
+  @override
+  void dispose() {
+    parent = null; 
+    routerDelegate.parent = null;
+    super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
+    // The parent will only be null, if this state is disposed and therefore 
+    // `build` cannot be called on it any more.
     final backButtonDispatcher = widget.backButtonDispatcher ??
-        ((parent.backButtonDispatcher is BeamerBackButtonDispatcher &&
+        ((parent!.backButtonDispatcher is BeamerBackButtonDispatcher &&
                 widget.createBackButtonDispatcher)
             ? BeamerChildBackButtonDispatcher(
                 parent:
-                    parent.backButtonDispatcher! as BeamerBackButtonDispatcher,
+                    parent!.backButtonDispatcher! as BeamerBackButtonDispatcher,
                 delegate: routerDelegate,
               )
             : null);
diff --git a/package/lib/src/beamer_delegate.dart b/package/lib/src/beamer_delegate.dart
index 2db29624..38ed3c87 100644
--- a/package/lib/src/beamer_delegate.dart
+++ b/package/lib/src/beamer_delegate.dart
@@ -74,7 +74,13 @@ class BeamerDelegate extends RouterDelegate<RouteInformation>
   /// `*App.router` and at least one more [Beamer] in the Widget tree.
   BeamerDelegate? get parent => _parent;
   set parent(BeamerDelegate? parent) {
-    if (parent == null || _parent == parent) {
+    if(parent == null && _parent != null) {
+      _parent!.removeListener(_updateFromParent);
+      _parent!._children.remove(this);
+      _parent = null;
+      return;
+    }
+    if (_parent == parent) {
       return;
     }
     _parent = parent;
@@ -398,7 +404,7 @@ class BeamerDelegate extends RouterDelegate<RouteInformation>
 
     // run guards on _beamLocationCandidate
     final context = _context;
-    if (context != null && context is Element && (context as Element).dirty == false) {      
+    if (context != null) {
       final didApply = _runGuards(context, _beamLocationCandidate);
       _didRunGuards = true;
       if (didApply) {