made some minor changes

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);
+}