try to ensure only one pop occurs

Author: julian-CStack

lib/pages/signing/sub_widgets/sign_message_tab.dart

@@ -90,7 +90,7 @@ class _SignMessageFormState extends ConsumerState<SignMessageForm> {
 
     messageController.text = ref.read(_pSignState).message;
 
-    _chooseAddress = IfNotAlreadyAsync(() async {
+    _chooseAddress = IfNotAlreadyAsync<void>(() async {
       final Address? address;
 
       if (Util.isDesktop) {
@@ -166,7 +166,7 @@ class _SignMessageFormState extends ConsumerState<SignMessageForm> {
       }
     }).execute;
 
-    _sign = IfNotAlreadyAsync(() async {
+    _sign = IfNotAlreadyAsync<void>(() async {
       Exception? ex;
 
       final state = ref.read(_pSignState);

lib/pages/signing/sub_widgets/verify_message_tab.dart

@@ -82,7 +82,7 @@ class _VerifyMessageFormState extends ConsumerState<VerifyMessageForm> {
     messageController.text = ref.read(_pVerifyState).message;
     signatureController.text = ref.read(_pVerifyState).signature;
 
-    _verify = IfNotAlreadyAsync(() async {
+    _verify = IfNotAlreadyAsync<void>(() async {
       Exception? ex;
 
       final verified = await showLoading(

lib/utilities/if_not_already.dart

@@ -18,18 +18,24 @@ class IfNotAlready {
   }
 }
 
-class IfNotAlreadyAsync {
-  final Future<void> Function() _function;
+class IfNotAlreadyAsync<T> {
+  final Future<void> Function()? _function;
+  final Future<void> Function(T? args)? _functionWithArgs;
 
   bool _locked = false;
 
-  IfNotAlreadyAsync(this._function);
+  IfNotAlreadyAsync(this._function) : _functionWithArgs = null;
+  IfNotAlreadyAsync.withArgs(this._functionWithArgs) : _function = null;
 
-  Future<void> execute() async {
+  Future<void> execute([T? args]) async {
     if (!_locked) {
       _locked = true;
       try {
-        await _function();
+        if (_function == null) {
+          await _function!();
+        } else {
+          await _functionWithArgs!(args);
+        }
       } finally {
         _locked = false;
       }

lib/widgets/qr_scanner.dart

@@ -5,6 +5,7 @@ import 'package:flutter/material.dart';
 import 'package:qr_code_scanner_plus/qr_code_scanner_plus.dart';
 
 import '../themes/stack_colors.dart';
+import '../utilities/if_not_already.dart';
 import '../utilities/text_styles.dart';
 import 'background.dart';
 import 'custom_buttons/app_bar_icon_button.dart';
@@ -23,10 +24,18 @@ class _QrScannerState extends State<QrScanner> {
 
   StreamSubscription<Barcode>? sub;
 
-  void _onScanned(String? data) {
-    if (data != null && mounted) {
-      Navigator.of(context).pop(data);
-    }
+  late final Future<void> Function(String?) _onScanned;
+
+  @override
+  void initState() {
+    super.initState();
+
+    _onScanned = IfNotAlreadyAsync<String>.withArgs((data) async {
+      await sub?.cancel();
+      if (mounted) {
+        Navigator.of(context).pop(data);
+      }
+    }).execute;
   }
 
   // In order to get hot reload to work we need to pause the camera if the platform