ok, Fenster ist da, ich komme auf die main und auf die about page und auch von da zurück zur main; Inhalt main page fehlt

Project_Periodensystem.Controller/Project_Periodensystem.Controller.csproj

@@ -6,7 +6,7 @@
   </ItemGroup>
 
   <PropertyGroup>
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>

Project_Periodensystem.Model/Project_Periodensystem.Model.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>

Project_Periodensystem.Persistence/Project_Periodensystem.Persistence.csproj

@@ -2,7 +2,7 @@
   <!-- PropertyGroup enthält verschiedene Projekteinstellungen -->
   <PropertyGroup>
     <!-- Gibt die Ziel-.NET-Framework-Version an -->
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <!-- Aktiviert implizite Verwendungen, die automatisch häufig verwendete Namespaces importieren -->
     <ImplicitUsings>enable</ImplicitUsings>
     <!-- Aktiviert nullable Referenztypen zur Unterstützung der Nullsicherheitsprüfung -->

Project_Periodensystem.View/AboutPage.axaml

@@ -0,0 +1,12 @@
+<!-- Datei: Project_Periodensystem.View/AboutPage.axaml -->
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:i="using:Avalonia.Interactivity"
+             x:Class="Project_Periodensystem.View.AboutPage">
+  <Grid>
+    <Button x:Name="BackButton" 
+            Click="BackButton_Click">
+        Back
+    </Button>
+  </Grid>
+</UserControl>

Project_Periodensystem.View/AboutPage.axaml.cs

@@ -0,0 +1,27 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+using Avalonia.VisualTree;
+
+namespace Project_Periodensystem.View
+{
+    public partial class AboutPage : UserControl
+    {
+        public AboutPage()
+        {
+            InitializeComponent();
+        }
+
+        private void InitializeComponent()
+            => AvaloniaXamlLoader.Load(this);
+
+        private void BackButton_Click(object sender, RoutedEventArgs e)
+        {
+            var window = this.GetVisualRoot() as MainWindow;
+            if (window != null)
+            {
+                window.ShowLanding();
+            }
+        }
+    }
+}

Project_Periodensystem.View/App.axaml

@@ -1,7 +1,6 @@
 <Application xmlns="https://github.com/avaloniaui"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-             x:Class="Project_Periodensystem.View.App"
+             x:Class="Project_Periodensystem.View.App">
-             RequestedThemeVariant="Light">
   <Application.Styles>
     <FluentTheme />
   </Application.Styles>

Project_Periodensystem.View/App.axaml.cs

@@ -7,12 +7,16 @@ namespace Project_Periodensystem.View
     public partial class App : Application
     {
         public override void Initialize()
-            => AvaloniaXamlLoader.Load(this);
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
 
         public override void OnFrameworkInitializationCompleted()
         {
             if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
+            {
                 desktop.MainWindow = new MainWindow();
+            }
 
             base.OnFrameworkInitializationCompleted();
         }

Project_Periodensystem.View/LandingPage.axaml

@@ -0,0 +1,22 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="Project_Periodensystem.View.LandingPage">
+  <Grid>
+    <TextBlock Text="Welcome to the periodic table of elements!"
+               HorizontalAlignment="Center"
+               VerticalAlignment="Center"
+               FontSize="32"
+               Foreground="Red"
+               Margin="0,0,0,60"/>
+    <Button x:Name="StartButton" 
+            Content="Start"
+            HorizontalAlignment="Center"
+            VerticalAlignment="Center"
+            Margin="0,60,0,0"
+            Width="160"
+            Height="50"
+            Background="Red"
+            Foreground="White"
+            Click="StartButton_Click"/>
+  </Grid>
+</UserControl>

Project_Periodensystem.View/LandingPage.axaml.cs

@@ -0,0 +1,29 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+using Avalonia.VisualTree;
+
+namespace Project_Periodensystem.View
+{
+    public partial class LandingPage : UserControl
+    {
+        public LandingPage()
+        {
+            InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+
+        private void StartButton_Click(object sender, RoutedEventArgs e)
+        {
+            var window = this.GetVisualRoot() as MainWindow;
+            if (window != null)
+            {
+                window.ShowPeriodicTable();
+            }
+        }
+    }
+}

Project_Periodensystem.View/MainWindow.axaml

@@ -1,23 +1,9 @@
 <Window xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:vm="clr-namespace:Project_Periodensystem.Controller;assembly=Project_Periodensystem.Controller"
-        xmlns:components="clr-namespace:Project_Periodensystem.View.Components;assembly=Project_Periodensystem.View"
         x:Class="Project_Periodensystem.View.MainWindow"
         Title="Periodensystem"
-        Width="900" Height="650"
+        Width="900" Height="650">
-        CanResize="True"
+    <Grid>
-        Background="#111111">
+        <ContentControl x:Name="MainContent"/>
-
+    </Grid>
-  <!-- DataContext auf den Controller setzen -->
-  <Window.DataContext>
-    <vm:PeriodensystemController />
-  </Window.DataContext>
-
-  <ScrollViewer HorizontalScrollBarVisibility="Auto"
-                VerticalScrollBarVisibility="Auto">
-    <!-- Canvas mit fester Größe: 18 Spalten × 80px = 1440px, 10 Zeilen × 80px = 800px -->
-    <Canvas x:Name="PeriodicCanvas"
-            Width="1440"
-            Height="800" />
-  </ScrollViewer>
 </Window>

Project_Periodensystem.View/MainWindow.axaml.cs

@@ -1,46 +1,41 @@
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
-using Project_Periodensystem.Controller;
-using Project_Periodensystem.View.Components;
 
 namespace Project_Periodensystem.View
 {
     public partial class MainWindow : Window
     {
-        private readonly PeriodensystemController _controller;
+        private readonly ContentControl mainContent;
 
         public MainWindow()
         {
             InitializeComponent();
-            _controller = new PeriodensystemController();
+            var content = this.Find<ContentControl>("MainContent");
-            DataContext = _controller;
+            if (content == null)
-            PopulateCanvas();
+                throw new System.Exception("MainContent control not found.");
+            
+            mainContent = content;
+            ShowLanding(); // Show initial page
         }
 
         private void InitializeComponent()
-            => AvaloniaXamlLoader.Load(this);
-
-        private void PopulateCanvas()
         {
-            // Holt den Canvas aus dem XAML (muss existieren!)
+            AvaloniaXamlLoader.Load(this);
-            var canvas = this.FindControl<Canvas>("PeriodicCanvas");
-            if (canvas == null)
-                return;
-
-            foreach (var element in _controller.Elements)
-            {
-                // Neues Tile für jedes Element
-                var tile = new ElementTile
-                {
-                    DataContext = element
-                };
-
-                // Position setzen: Column × 80px, Row × 80px
-                Canvas.SetLeft(tile, element.Column * 80);
-                Canvas.SetTop(tile,  element.Row    * 80);
-
-                canvas.Children.Add(tile);
         }
+
+        public void ShowLanding()
+        {
+            mainContent.Content = new LandingPage();
+        }
+
+        public void ShowPeriodicTable()
+        {
+            mainContent.Content = new PeriodicTablePage();
+        }
+
+        public void ShowAbout()
+        {
+            mainContent.Content = new AboutPage();
         }
     }
 }

Project_Periodensystem.View/PeriodicTablePage.axaml

@@ -0,0 +1,11 @@
+<!-- PeriodicTablePage.axaml -->
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="Project_Periodensystem.View.PeriodicTablePage">
+  <Grid>
+    <Button Name="AboutButton" 
+            Click="AboutButton_Click">
+        About
+    </Button>
+  </Grid>
+</UserControl>

Project_Periodensystem.View/PeriodicTablePage.axaml.cs

@@ -0,0 +1,29 @@
+using Avalonia.Controls;
+using Avalonia.Interactivity;
+using Avalonia.Markup.Xaml;
+using Avalonia.VisualTree;
+
+namespace Project_Periodensystem.View
+{
+    public partial class PeriodicTablePage : UserControl
+    {
+        public PeriodicTablePage()
+        {
+            InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+
+        private void AboutButton_Click(object sender, RoutedEventArgs e)
+        {
+            var window = this.GetVisualRoot() as MainWindow;
+            if (window != null)
+            {
+                window.ShowAbout();
+            }
+        }
+    }
+}

Project_Periodensystem.View/Program.cs

@@ -1,14 +1,15 @@
-using System;
+using Avalonia;
-using Avalonia;
 
 namespace Project_Periodensystem.View
 {
-    class Program
+    internal static class Program
     {
-        [STAThread]
+        [System.STAThread] // <-- Das ist korrekt!
         public static void Main(string[] args)
-            => BuildAvaloniaApp()
+        {
+            BuildAvaloniaApp()
                 .StartWithClassicDesktopLifetime(args);
+        }
 
         public static AppBuilder BuildAvaloniaApp()
             => AppBuilder.Configure<App>()

Project_Periodensystem.View/Project_Periodensystem.View.csproj

@@ -1,32 +1,25 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
     <OutputType>WinExe</OutputType>
-    <TargetFramework>net9.0</TargetFramework>
     <Nullable>enable</Nullable>
-    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <UseWPF>false</UseWPF>
-    <ApplicationManifest>app.manifest</ApplicationManifest>
+    <UseWindowsForms>false</UseWindowsForms>
-
-    <!-- Wichtig: Sagt MSBuild, dass Avalonia benutzt wird -->
-    <UseAvalonia>true</UseAvalonia>
-
-    <!-- Optional, für bessere Performance bei Bindings -->
-    <AvaloniaUseCompiledBindingsByDefault>false</AvaloniaUseCompiledBindingsByDefault>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Avalonia" Version="11.2.6" />
+    <PackageReference Include="Avalonia" Version="11.0.0" />
-    <PackageReference Include="Avalonia.Desktop" Version="11.2.6" />
+    <PackageReference Include="Avalonia.Desktop" Version="11.0.0" />
-    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.2.6" />
+    <PackageReference Include="Avalonia.Diagnostics" Version="11.0.0" />
-    <PackageReference Include="Avalonia.Fonts.Inter" Version="11.2.6" />
+    <PackageReference Include="Avalonia.ReactiveUI" Version="11.0.0" />
-    <PackageReference Include="Avalonia.Diagnostics" Version="11.2.6">
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.0.0" />
-      <IncludeAssets Condition="'$(Configuration)' != 'Debug'">None</IncludeAssets>
-      <PrivateAssets Condition="'$(Configuration)' != 'Debug'">All</PrivateAssets>
-    </PackageReference>
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\Project_Periodensystem.Controller\Project_Periodensystem.Controller.csproj" />
+    <ProjectReference Include="..\Project_Periodensystem.Model\Project_Periodensystem.Model.csproj" />
+    <ProjectReference Include="..\Project_Periodensystem.Persistence\Project_Periodensystem.Persistence.csproj" />
   </ItemGroup>
 
 </Project>