stop timer when page disappears. autofocus camera.

src/App/Pages/ScanPage.cs

@@ -11,6 +11,7 @@ namespace Bit.App.Pages
     {
         private readonly ZXingScannerView _zxing;
         private readonly OverlayGrid _overlay;
+        private bool _pageDisappeared = true;
 
         public ScanPage(Action<string> callback)
             : base(updateActivity: false)
@@ -78,12 +79,24 @@ namespace Bit.App.Pages
 
         protected override void OnAppearing()
         {
+            _pageDisappeared = false;
             base.OnAppearing();
             _zxing.IsScanning = true;
+            Device.StartTimer(new TimeSpan(0, 0, 2), () =>
+            {
+                if(_pageDisappeared)
+                {
+                    return false;
+                }
+
+                _zxing.AutoFocus();
+                return true;
+            });
         }
 
         protected override void OnDisappearing()
         {
+            _pageDisappeared = true;
             _zxing.IsScanning = false;
             base.OnDisappearing();
         }

src/App/Pages/Tools/ToolsAutofillServicePage.cs

@@ -12,6 +12,7 @@ namespace Bit.App.Pages
     {
         private readonly IGoogleAnalyticsService _googleAnalyticsService;
         private readonly IAppInfoService _appInfoService;
+        private bool _pageDisappeared = false;
 
         public ToolsAutofillServicePage()
         {
@@ -170,6 +171,11 @@ namespace Bit.App.Pages
             UpdateEnabled();
             Device.StartTimer(new TimeSpan(0, 0, 3), () =>
             {
+                if(_pageDisappeared)
+                {
+                    return false;
+                }
+                
                 UpdateEnabled();
                 return true;
             });
@@ -178,6 +184,18 @@ namespace Bit.App.Pages
             Content = ScrollView;
         }
 
+        protected override void OnAppearing()
+        {
+            _pageDisappeared = false;
+            base.OnAppearing();
+        }
+
+        protected override void OnDisappearing()
+        {
+            _pageDisappeared = true;
+            base.OnDisappearing();
+        }
+
         private void UpdateEnabled()
         {
             ScrollView.Content = _appInfoService.AutofillServiceEnabled ? EnabledStackLayout : DisabledStackLayout;

src/App/Pages/Vault/VaultViewLoginPage.cs

@@ -21,6 +21,7 @@ namespace Bit.App.Pages
         private readonly IUserDialogs _userDialogs;
         private readonly IDeviceActionService _deviceActionService;
         private readonly ITokenService _tokenService;
+        private bool _pageDisappeared = true;
 
         public VaultViewLoginPage(string loginId)
         {
@@ -153,6 +154,7 @@ namespace Bit.App.Pages
 
         protected async override void OnAppearing()
         {
+            _pageDisappeared = false;
             NotesCell.Tapped += NotesCell_Tapped;
             EditItem.InitEvents();
 
@@ -217,6 +219,11 @@ namespace Bit.App.Pages
                         TotpTick(totpKey);
                         Device.StartTimer(new TimeSpan(0, 0, 1), () =>
                         {
+                            if(_pageDisappeared)
+                            {
+                                return false;
+                            }
+
                             TotpTick(totpKey);
                             return true;
                         });
@@ -253,6 +260,7 @@ namespace Bit.App.Pages
 
         protected override void OnDisappearing()
         {
+            _pageDisappeared = true;
             NotesCell.Tapped -= NotesCell_Tapped;
             EditItem.Dispose();
             CleanupAttachmentCells();