try to use IEventAggregator and IHandle

Gremlin/MVVM/AppBootstrapper.cs

@@ -4,13 +4,21 @@ namespace Gremlin.MVVM
 {
     public class AppBootstrapper : BootstrapperBase
     {
+        private readonly SimpleContainer _container = new();
+
         public AppBootstrapper()
         {
             Initialize();
         }
 
+        protected override void Configure()
+        {
+            _container.Singleton<IEventAggregator, EventAggregator>();
+        }
+
         protected override void OnStartup(object sender, System.Windows.StartupEventArgs e)
         {
+            //LogManager.GetLog = type => new DebugLog(type); //DEBUGGING
             DisplayRootViewFor<ShellViewModel>();
         }
     }

Gremlin/MVVM/ViewModels/AllContactsViewModel.cs

@@ -7,17 +7,32 @@ using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace Gremlin.MVVM
 {
-    public class AllContactsViewModel : PropertyChangedBase
+    public class AllContactsViewModel : PropertyChangedBase, IHandle<ShellViewModel>
     {
         private ObservableCollection<ContactViewModel> _allContactsVM;
+        private IEventAggregator _eventAggregator;
+
         public ObservableCollection<ContactViewModel> AllContactsVM { get => _allContactsVM; internal set { _allContactsVM = value; NotifyOfPropertyChange(() => AllContactsVM); } }
 
-        public AllContactsViewModel() 
+        //public AllContactsViewModel() 
+        //{
+        //    LoadContacts();
+        //}
+
+        public AllContactsViewModel(IEventAggregator eventAggregator)
         {
+            _eventAggregator = eventAggregator;
             LoadContacts();
+            _eventAggregator.PublishOnUIThreadAsync($"{AllContactsVM.Count} Contacts loaded.");
+        }
+
+        public AllContactsViewModel()
+        {
         }
 
         public void LoadContacts()
@@ -50,5 +65,10 @@ namespace Gremlin.MVVM
                 throw;
             }
         }
+
+        public Task HandleAsync(ShellViewModel message, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
     }
 }

Gremlin/MVVM/ViewModels/ContactViewModel.cs

@@ -3,10 +3,12 @@ using System.Text;
 using System.Windows.Data;
 using Gremlin.GremlinData.EntityClasses;
 using Caliburn.Micro;
+using System.Threading.Tasks;
+using System.Threading;
 
 namespace Gremlin.MVVM
 {
-    public class ContactViewModel : PropertyChangedBase
+    public class ContactViewModel : PropertyChangedBase, IHandle<ShellViewModel>
     {
         private byte _gender;
         private string _firstName;
@@ -16,6 +18,7 @@ namespace Gremlin.MVVM
         private string _accountStreet;
         private uint _accountZIP;
         private string _accountCity;
+        private IEventAggregator _eventAggregator;
 
         public byte Gender { get => _gender; internal set { _gender = value; NotifyOfPropertyChange(() => Gender); } }
         public string FirstName { get => _firstName; internal set { _firstName = value; NotifyOfPropertyChange(() => FirstName); } }
@@ -26,7 +29,10 @@ namespace Gremlin.MVVM
         public uint AccountZIP { get => _accountZIP; internal set { _accountZIP = value; NotifyOfPropertyChange(() => AccountZIP); } }
         public string AccountCity { get => _accountCity; internal set { _accountCity = value; NotifyOfPropertyChange(() => AccountCity); } }
 
-        public ContactViewModel() { }
+        public ContactViewModel(IEventAggregator eventAggregator)
+        {
+            _eventAggregator = eventAggregator;
+        }
 
         public ContactViewModel(byte gender, string firstName, string lastName, string eMail, string accountName, string accountStreet, uint accountZIP, string accountCity)
         {
@@ -40,6 +46,10 @@ namespace Gremlin.MVVM
             AccountCity = accountCity ?? throw new ArgumentNullException(nameof(accountCity));
         }
 
+        public ContactViewModel()
+        {
+        }
+
         internal static ContactViewModel ConvertObjectToContactVM(object selectedItem)
         {
             ContactViewModel selectedContact = new();
@@ -178,5 +188,9 @@ namespace Gremlin.MVVM
             return briefkopf;
         }
 
+        public Task HandleAsync(ShellViewModel message, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
     }
 }

Gremlin/MVVM/ViewModels/QuoteViewModel.cs

@@ -2,10 +2,12 @@
 using System;
 using System.Collections.ObjectModel;
 using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace Gremlin.MVVM
 {
-    public class QuoteViewModel : PropertyChangedBase
+    public class QuoteViewModel : PropertyChangedBase, IHandle<ShellViewModel>
     {
         private string _quoteType = "ein Analysegerät";
         private string _quotePath;
@@ -27,6 +29,7 @@ namespace Gremlin.MVVM
         private bool _quoteContains3PP;
         private bool _quoteContainsRB;
         private bool? _showDiscounts = true;
+        private IEventAggregator _eventAggregator;
 
         public string QuoteType { get => _quoteType; internal set { _quoteType = value; NotifyOfPropertyChange(() => QuoteType); } }
         public string QuotePath { get => _quotePath; internal set { _quotePath = value; NotifyOfPropertyChange(() => QuotePath); } }
@@ -62,7 +65,7 @@ namespace Gremlin.MVVM
             };
         }
 
-        public QuoteViewModel() { }
+        //public QuoteViewModel() { }
 
         private QuoteViewModel(string quoteNumber, string quoteType, ContactViewModel recipient, ContactViewModel salesRep, bool? brutto, float vAT, int warranty, int validity, string quotePath, bool? singlePrices, bool? brochures, bool? dataSheets, bool? mailTemplate, bool? showDiscounts)
         {
@@ -82,6 +85,15 @@ namespace Gremlin.MVVM
             ShowDiscounts = showDiscounts;
         }
 
+        public QuoteViewModel(IEventAggregator eventAggregator)
+        {
+            _eventAggregator = eventAggregator;
+        }
+
+        public QuoteViewModel()
+        {
+        }
+
         internal static QuoteViewModel CreateQuote(string quoteNumber, ContactViewModel recipient, ContactViewModel salesRep, float vAT = 19f, string quoteType = "ein Analysegerät", bool? brutto = true, int warranty = 12, bool? singlePrices = true, bool? brochures = true, bool? dataSheets = true, bool? mailTemplate = true, string quotePath = "", int validity = 60, bool? showDiscounts = true)
         {
             decimal totalListprice = 0, totalDiscount = 0, calcTotalNet = 0;
@@ -149,5 +161,10 @@ namespace Gremlin.MVVM
         {
             LineItemsViewModel = LineItemViewModel.ReadLineItemsFromClipboard();
         }
+
+        public Task HandleAsync(ShellViewModel message, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
     }
 }

Gremlin/MVVM/ViewModels/ShellViewModel.cs

@@ -1,14 +1,43 @@
-namespace Gremlin.MVVM
+using Caliburn.Micro;
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Gremlin.MVVM
 {
-    public class ShellViewModel
+    public class ShellViewModel : PropertyChangedBase, IHandle<QuoteViewModel> ,IHandle<AllContactsViewModel>
     {
-        public QuoteViewModel QuoteVM { get; set; }
+        private AllContactsViewModel allContactsVM;
-        public AllContactsViewModel AllContactsVM { get; set; }
+        private QuoteViewModel quoteVM;
+        private readonly IEventAggregator _eventAggregator;
+
+        public QuoteViewModel QuoteVM { get => quoteVM; set => quoteVM = value; }
+        public AllContactsViewModel AllContactsVM { get => allContactsVM; set => allContactsVM = value; }
 
         public ShellViewModel()
         {
             QuoteVM = new();
             AllContactsVM = new();
         }
+
+        public ShellViewModel(IEventAggregator eventAggregator)
+        {
+            QuoteVM = new QuoteViewModel(eventAggregator);
+            AllContactsVM = new AllContactsViewModel(eventAggregator);
+
+            _eventAggregator = eventAggregator;
+            _eventAggregator.PublishOnUIThreadAsync($"{AllContactsVM.AllContactsVM.Count} Contacts loaded.");
+            _eventAggregator.PublishOnUIThreadAsync(12);
+        }
+
+        public Task HandleAsync(AllContactsViewModel message, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
+
+        public Task HandleAsync(QuoteViewModel message, CancellationToken cancellationToken)
+        {
+            throw new NotImplementedException();
+        }
     }
 }