Full refactor:

  * Rethinking application separation (see new folder and namespace structure).
  * Splitting commands into Partial Views, so the ViewModels will not be very long due to the many commands.
  * Complete rewriting and improvement of command and input data logic processing for better transparency and readability.
  * Defined are enums, static classes.
  * Removed previously created Handlers and their associated interfaces.
  * The individual elements have been removed from the global resource because they are not global but static, so they have been associated with the corresponding Views.
  * Removing individual behaviors because can be made these functions also with Commands.
  * Defined AppCacheStorage on client side.
    * The storage uses the Default Memory Cache.
    * Some data is stored in a cache for easier data processing on the client side.
  * Defined AppUserService on client side.
    * This service manages the signed in user on the client side.
  * Defined ViewNavigator on client side.
    * The ViewNavigator implements which view is visible in Main Window.
  * The SignalR management has been outsourced to a separate service on the client side.
    * The full Hub management for ChatHub has been added to the SignalRChatHub service and removed from the MainWindowViewModel.
    * The Hubs will be those Singleton instances.
  * Defined the AsynObservableCollection - ObservableCollection Extension into the Client Project.
  * Defined Log4Net into Client and Server Side.
  * Configured the application that the app run in a Dev or Prod environment.
    * Created of the corresponding Environment Service.
  * Replaced the ServiceLocator.
    * Defined a Dependency Injector that allows you to register Sigelton and Transient dependencies.
    * Created a bootstrapper whose Init method registers all dependency connections into the Container.
    * Overrided OnStartup() method, that is, this is where the dependencies are registered into the Container.
  * Managed globally unhandled exceptions.
    * Unhandled exceptions appear in an ErrorWindow.
    * The text that is displayed depends on whether the application is running in a Dev or Prod environment.
  * Defined custom exceptions.
  * On the Client and Server side, the Send Unicast Notification and Send Broadcast Notification operations have been removed as they do not belong to a basic chat application.
  * On the Client and Server side, the configuration settings that have been burned into code so far have been outsourced to the app.config file.
  * Unity DI Container has also been implemented on the server side.
  * A repository has been created on the server side to manage participants (this will be a singelton instance).

Author: Sullivan008

Application.Client/App.config

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <configSections>
+    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, Log4net" />
+    <section name="SignalRConfiguration" type="Application.Client.Core.AppConfigurations.SignalR.ConfigurationSections.SignalRConfigurationSection, Application.Client"/>
+  </configSections>
+  <log4net>
+    <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender,log4net">
+      <param name="File" value="logs\logs.log" />
+      <param name="AppendToFile" value="true" />
+      <param name="MaxSizeRollBackups" value="10" />
+      <param name="MaximumFileSize" value="10240KB" />
+      <param name="RollingStyle" value="Size" />
+      <param name="StaticLogFileName" value="true" />
+      <layout type="log4net.Layout.PatternLayout,log4net">
+        <param name="ConversionPattern" value="[%level] - %date - %type.%method, row: %line - %message%n" />
+      </layout>
+    </appender>
+    <root>
+      <level value="ALL" />
+      <appender-ref ref="RollingLogFileAppender" />
+    </root>
+  </log4net>
+  <SignalRConfiguration>
+    <HubConnectionConfiguration Url="http://localhost:8080/signalchat" />
+    <ChatHubConfiguration HubName="ChatHub" ReconnectTimeInterval="1000" />
+  </SignalRConfiguration>
+  <appSettings>
+    <add key="ENVIRONMENT_TYPE" value="0"/>
+  </appSettings>
+  <startup>
+    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2" />
+  </startup>
+  <system.net>
+    <connectionManagement>
+      <add address="*" maxconnection="1" />
+    </connectionManagement>
+  </system.net>
+  <runtime>
+    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
+      <dependentAssembly>
+        <assemblyIdentity name="log4net" publicKeyToken="669e0ddf0bb1aa2a" culture="neutral" />
+        <bindingRedirect oldVersion="0.0.0.0-2.0.12.0" newVersion="2.0.12.0" />
+      </dependentAssembly>
+    </assemblyBinding>
+  </runtime>
+</configuration>

Application.Client/App.xaml

@@ -0,0 +1,26 @@
+<Application x:Class="Application.Client.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:chatView="clr-namespace:Application.Client.Views.Chat"
+             xmlns:chatViewModels="clr-namespace:Application.Client.Views.Chat.ViewModels"
+             xmlns:signInView="clr-namespace:Application.Client.Views.SignIn"
+             xmlns:signInViewModels="clr-namespace:Application.Client.Views.SignIn.ViewModels"
+             Startup="App_OnStartup">
+    <Application.Resources>
+        <ResourceDictionary>
+            <ResourceDictionary.MergedDictionaries>
+                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
+                <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Colors.xaml" />
+                <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Light.xaml" />
+                <ResourceDictionary Source="pack://application:,,,/MaterialDesignColors;component/Themes/Recommended/Primary/MaterialDesignColor.Blue.xaml" />
+            </ResourceDictionary.MergedDictionaries>
+
+            <DataTemplate DataType="{x:Type signInViewModels:SignInViewModel}">
+                <signInView:SignInView/>
+            </DataTemplate>
+            <DataTemplate DataType="{x:Type chatViewModels:ChatViewModel}">
+                <chatView:ChatView/>
+            </DataTemplate>
+        </ResourceDictionary>
+    </Application.Resources>
+</Application>

Application.Client/App.xaml.cs

@@ -0,0 +1,54 @@
+using System.Windows;
+using System.Windows.Threading;
+using Application.Client.Container;
+using Application.Client.Container.Unity;
+using Application.Client.Core.Environment.Enums;
+using Application.Client.Core.Environment.Services.Interfaces;
+using Application.Client.Core.Exceptions.Models;
+using Application.Client.Windows.Main;
+
+namespace Application.Client
+{
+    public partial class App
+    {
+        private IEnvironmentService _environmentService;
+
+        protected override void OnStartup(StartupEventArgs e)
+        {
+            base.OnStartup(e);
+
+            log4net.Config.XmlConfigurator.Configure();
+
+            Bootstrapper.Init();
+
+            _environmentService = DependencyInjector.Retrieve<IEnvironmentService>();
+
+            DependencyInjector.Retrieve<MainWindow>().Show();
+        }
+
+        private void App_OnStartup(object sender, StartupEventArgs e)
+        {
+            Current.DispatcherUnhandledException += AppDispatcherUnhandledException;
+        }
+
+        private void AppDispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs e)
+        {
+            EnvironmentType environmentType = _environmentService.GetEnvironmentType();
+            ErrorModel errorModel = new ErrorModel(environmentType, e.Exception);
+
+            ShowUnhandledException(errorModel);
+
+            e.Handled = true;
+        }
+
+        private static void ShowUnhandledException(ErrorModel errorModel)
+        {
+            string errorMessage = $"An application error occured.\n\n{errorModel.Message}.\n\n{errorModel.Exception}";
+
+            if (MessageBox.Show(errorMessage, "Application Error", MessageBoxButton.OK, MessageBoxImage.Error) == MessageBoxResult.OK)
+            {
+                Current.Shutdown();
+            }
+        }
+    }
+}