made some minor changes

App.axaml.cs

@@ -16,7 +16,7 @@ public partial class App : Application
     {
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
-            desktop.MainWindow = new MainWindow(desktop.Args);
+            desktop.MainWindow = new MainWindow();
         }
         base.OnFrameworkInitializationCompleted();
     }

MainWindow.axaml

@@ -5,58 +5,87 @@
         xmlns:vm="clr-namespace:SimpleNote"
         mc:Ignorable="d" d:DesignWidth="40" d:DesignHeight="200"
         x:Class="SimpleNote.MainWindow"
-        x:DataType="vm:MainViewModel"
+        x:DataType="vm:ViewModel"
-        WindowStartupLocation="CenterScreen"
+        WindowStartupLocation="Manual"
-        TransparencyLevelHint="AcrylicBlur"
+        TransparencyLevelHint="Transparent"
+        TransparencyBackgroundFallback="DimGray"
         Background="Transparent"
         Height="50"
-        Width="{Binding WindowWidth}"
         SystemDecorations="None"
-        ExtendClientAreaToDecorationsHint="False"
+        ExtendClientAreaToDecorationsHint="True"
         CanResize="False"
         Topmost="True"
         Title="SimpleNote">
-
+        <Window.Styles>
-        <Panel>
+                <Style Selector="TextBox">
+                        <Style Selector="^:focus">
+                                <Setter Property="BorderBrush" Value="Transparent"/>
+                                <Style Selector="^ /template/ Border#PART_BorderElement">
+                                        <Setter Property="Background" Value="Transparent"/>
+                                        <Setter Property="BorderBrush" Value="Transparent"/>
+                                        <Setter Property="BorderThickness" Value="1" />
+                                </Style>
+                        </Style>
+                        <Style Selector="^:pointerover /template/ Border#PART_BorderElement">
+                                <Setter Property="BorderBrush" Value="Transparent"/>
+                                <Setter Property="Background" Value="Transparent" />
+                        </Style>
+                </Style>
+        </Window.Styles>
+        <!--<Border CornerRadius="15" BorderBrush="White" BorderThickness="2" Background="#000000aa">-->
+                <StackPanel Orientation="Horizontal">
                         <ExperimentalAcrylicBorder IsHitTestVisible="False">
                                 <ExperimentalAcrylicBorder.Material>
                                         <ExperimentalAcrylicMaterial
                                                 BackgroundSource="Digger"
-                                        TintColor="Black"
+                                                TintColor="Green"
-                                        TintOpacity="0.6"
+                                                TintOpacity="0.5"
                                                 MaterialOpacity="0.65" />
                                 </ExperimentalAcrylicBorder.Material>
                         </ExperimentalAcrylicBorder>
-                <TextBox HorizontalAlignment="Center"
+                        <TextBox x:Name="FocusBox" IsVisible="False"/>
-                         VerticalAlignment="Top"
+                        <Button Margin="5,0" Command="{Binding AddButtonPressedCommand}" FontSize="{Binding FontSize}" Width="40" HorizontalContentAlignment="Center">
-                         Height="5"
+                                +
-                         IsHitTestVisible="False"
+                        </Button>
-                         Margin="0, -3, 0, 0"
+                        <ItemsControl ItemsSource="{Binding Notes}">
-                         Foreground="Black"
+                                <ItemsControl.ItemsPanel>
-                         Text="SimpleNote - Note"
+                                        <ItemsPanelTemplate>
-                         Background="Transparent"
+                                                <StackPanel Orientation="Horizontal"/>
+                                        </ItemsPanelTemplate>
+                                </ItemsControl.ItemsPanel>
+                                <ItemsControl.ItemTemplate>
+                                        <DataTemplate x:DataType="vm:Note">
+                                                <Border CornerRadius="15" Margin="5,5,0,5" BorderBrush="#fff" BorderThickness="2" Background="Transparent">
+                                                        <StackPanel Margin="5" Background="Transparent" Orientation="Horizontal">
+                                                                <TextBox Height="20"
+                                                                         CaretBrush="Transparent"
                                                                          BorderThickness="0"
-                         FontSize="12"
+                                                                         Width="{Binding Width}"
-                         IsTabStop="False"
+                                                                         TextChanged="TextBox_OnTextChanged"
-                         IsReadOnly="True"
+                                                                         Margin="0, 0, 0, 0"
-                         >
-                </TextBox>
-                <TextBox x:Name="Note"
-                         Height="20"
-                         BorderThickness="0"
-                         Width="{Binding WindowWidth}"
-                         Margin="0, 12, 0, 0"
                                                                          Padding="5,0,5,0"
                                                                          TextAlignment="Center"
                                                                          HorizontalAlignment="Center"
                                                                          VerticalAlignment="Center"
                                                                          Foreground="White"
                                                                          Background="Transparent"
-                         IsHitTestVisible="False"
+                                                                         IsHitTestVisible="True"
                                                                          FontSize="{Binding FontSize}"
                                                                          IsTabStop="False"
-                         IsReadOnly="True"
+                                                                         IsReadOnly="False"
+                                                                         Text="{Binding Content}"
+                                                                         VerticalContentAlignment="Center"
+                                                                         KeyDown="InputElement_OnKeyDown"
                                                                 >
                                                                 </TextBox>
-        </Panel>
+                                                                <Button Command="{Binding RemoveButtonClicked}" FontSize="{Binding FontSize}" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Width="25" Padding="1,-3,0,0" Margin="5,0,0,0">
+                                                                        x
+                                                                </Button>
+                                                        </StackPanel>
+                                                </Border>
+                                        </DataTemplate>
+                                </ItemsControl.ItemTemplate>
+                        </ItemsControl>
+                </StackPanel>
+        <!--</Border>-->
 </Window>

MainWindow.axaml.cs

@@ -3,74 +3,89 @@ using System.ComponentModel;
 using Avalonia;
 using Avalonia.Controls;
 using System.Reactive.Linq;
+using Avalonia.Input;
+using Avalonia.Interactivity;
 using Avalonia.Media;
 
 namespace SimpleNote;
 
 public partial class MainWindow : Window
 {
-    private MainViewModel ViewModel;
+    private ViewModel viewModel;
-    public MainWindow(string[]? args)
+    private PixelRect? screen;
+    public MainWindow()
     {
-        if (args == null || args.Length < 1)
+        screen = Screens.Primary?.WorkingArea;
+        if (screen == null)
         {
-            Console.WriteLine("Call with Note as Argument!");
+            Console.WriteLine("No screen available.");
             Environment.Exit(1);
         }
+        
+        this.Position = new PixelPoint(screen.Value.Width / 2 - 25, 10);
+        this.Width = 50;
+        // this.MaxWidth = screen.Value.Width - 100;
+        
         InitializeComponent();
-        ViewModel = new MainViewModel();
+        viewModel = new ViewModel();
-        DataContext = ViewModel;
+        DataContext = viewModel;
 
         this.GetObservable(Window.WidthProperty)
             .Subscribe(width =>
             {
-                if (DataContext is MainViewModel vm)
+                if (DataContext is ViewModel vm)
                 {
                     vm.WindowWidth = (double)width;
                 }
             });
-
-        init_TextField(args[0]);
     }
 
+    /*
     public void init_TextField(string text)
     {
         var textBlock = new TextBlock
         {
             Text = text,
-            FontSize = ViewModel.FontSize,
+            FontSize = viewModel.FontSize,
             FontFamily = new FontFamily(FontFamily.DefaultFontFamilyName)
         };
         textBlock.Measure(Size.Infinity);
-        ViewModel.WindowWidth = textBlock.DesiredSize.Width + 50;
+        viewModel.WindowWidth = textBlock.DesiredSize.Width + 50;
         Note.Text = text;
     }
+    */
+
+    public static double TextWidth(string text)
+    {
+        var textBlock = new TextBlock
+        {
+            Text = text,
+            FontSize = ViewModel._fontSize,
+            FontFamily = new FontFamily(FontFamily.DefaultFontFamilyName)
+        };
+        textBlock.Measure(Size.Infinity);
+        return textBlock.DesiredSize.Width + 30 < 60 ? 60 : textBlock.DesiredSize.Width + 30;
     }
 
-public class MainViewModel : INotifyPropertyChanged
+    private void TextBox_OnTextChanged(object? sender, TextChangedEventArgs e)
     {
-    private double _windowWidth = 200;
+        if (sender == null) return;
-    private double _fontSize = 24;
+        ((TextBox)sender).Width = TextWidth(((TextBox)sender).Text);
-
+        double width = 55;
-    public double WindowWidth
+        foreach (var note in viewModel.Notes)
         {
-        get => _windowWidth;
+            width += note.Width + 49;
-        set
-        {
-            _windowWidth = value;
-            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(WindowWidth)));
-        }
         }
 
-    public double FontSize
+        if (width == 55) width -= 5;
-    {
+        
-        get => _fontSize;
+        this.Width = width;
-        set
+        this.Position = new PixelPoint((int)((screen.Value.Width - width) / 2), 10);
-        {
-            _fontSize = value;
-            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(FontSize)));
-        }
     }
 
-    public event PropertyChangedEventHandler? PropertyChanged;
+    private void InputElement_OnKeyDown(object? sender, KeyEventArgs e)
+    {
+        if (e.Key == Key.Enter)
+            this.Focus();
+    }
 }

SimpleNote.csproj

@@ -9,12 +9,13 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="Avalonia" Version="11.1.0" />
+        <PackageReference Include="Avalonia" Version="11.2.3" />
-        <PackageReference Include="Avalonia.Desktop" Version="11.1.0" />
+        <PackageReference Include="Avalonia.Desktop" Version="11.2.3" />
-        <PackageReference Include="Avalonia.Themes.Fluent" Version="11.1.0" />
+        <PackageReference Include="Avalonia.Themes.Fluent" Version="11.2.3" />
-        <PackageReference Include="Avalonia.Fonts.Inter" Version="11.1.0" />
+        <PackageReference Include="Avalonia.Fonts.Inter" Version="11.2.3" />
         <!--Condition below is needed to remove Avalonia.Diagnostics package from build output in Release configuration.-->
-        <PackageReference Condition="'$(Configuration)' == 'Debug'" Include="Avalonia.Diagnostics" Version="11.1.0" />
+        <PackageReference Condition="'$(Configuration)' == 'Debug'" Include="Avalonia.Diagnostics" Version="11.2.3" />
+        <PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0" />
         <PackageReference Include="System.Reactive.Linq" Version="6.0.1" />
     </ItemGroup>
 </Project>

ViewModel.cs

@@ -0,0 +1,115 @@
+using System;
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+using System.Windows.Input;
+using Avalonia.Interactivity;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+
+namespace SimpleNote;
+
+public class ViewModel : ObservableObject
+{
+    private double _windowWidth = 200;
+    public static double _fontSize = 20;
+    private double _noteWidth;
+    
+    public ObservableCollection<Note> Notes { get; set; } = new ObservableCollection<Note>();
+    public ICommand AddButtonPressedCommand { get; }
+
+    public ViewModel()
+    {
+        AddButtonPressedCommand = new RelayCommand(AddButtonPressedCommandEvent);
+    }
+    
+    public double WindowWidth
+    {
+        get => _windowWidth;
+        set => SetProperty(ref _windowWidth, value);
+    }
+
+    public double NoteWidth
+    {
+        get => _noteWidth;
+        set => SetProperty(ref _noteWidth, value);
+    }
+    
+    public double FontSize
+    {
+        get => _fontSize;
+        set => SetProperty(ref _fontSize, value);
+    }
+
+    private void AddButtonPressedCommandEvent(object? sender)
+    {
+        // TODO: generate new Note
+        AddNote();
+    }
+    
+    //[RelayCommand]
+    private void AddNote()
+    {
+        // Füge eine neue Note zur Collection hinzu
+        Note note = new Note
+        {
+            Width = MainWindow.TextWidth("New Note"), Content = "New Note", FontSize = FontSize,
+        };
+        note.RemoveButtonClicked = new RelayCommand(o => RemoveNote(note));
+        Notes.Add(note);
+        
+    }
+    
+    private void RemoveNote(Note note)
+    {
+        if (Notes.Contains(note))
+        {
+            Notes.Remove(note);
+        }
+    }
+    
+    public event PropertyChangedEventHandler? PropertyChanged;
+}
+
+public class Note : ObservableObject
+{
+    public double Width { get; set; }
+    public string _content;
+    public double FontSize { get; set; }
+    public RelayCommand RemoveButtonClicked { get; set; }
+
+    public string Content
+    {
+        get => _content;
+        set
+        {
+            _content = value;
+            Width = MainWindow.TextWidth(_content);
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Content)));
+        }
+    }
+    
+    public event PropertyChangedEventHandler? PropertyChanged;
+}
+
+public class RelayCommand : ICommand
+{
+    private readonly Action<object?> _execute;
+    private readonly Func<object?, bool>? _canExecute;
+
+    public event EventHandler? CanExecuteChanged;
+
+    public RelayCommand(Action<object?> execute, Func<object?, bool>? canExecute = null)
+    {
+        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
+        _canExecute = canExecute;
+    }
+
+    public bool CanExecute(object? parameter) =>
+        _canExecute?.Invoke(parameter) ?? true;
+
+    public void Execute(object? parameter) =>
+        _execute(parameter);
+
+    public void RaiseCanExecuteChanged() =>
+        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
+}