Update

ViewModel/AppDataFilePageVM.cs

@@ -0,0 +1,43 @@
+using System.ComponentModel;
+using System.Windows.Input;
+using FileReadAndWrite.Model;
+using FileReadAndWrite.Service;
+using FileReadAndWrite.View;
+
+namespace FileReadAndWrite.ViewModel;
+
+public class AppDataFilePageVM : INotifyPropertyChanged {
+    private readonly FileService _fileService;
+
+    private string _appDataFileContent = "";
+    public string AppDataFileContent { 
+        get => _appDataFileContent; 
+        set {
+            _appDataFileContent = value;
+            OnPropertyChanged(nameof(AppDataFileContent));
+        } 
+    }
+
+    public ICommand LoadAppDataFileCmd { get; }
+    public ICommand SaveAppDataFileCmd { get; }
+
+    public AppDataFilePageVM(FileService fileService) {
+        _fileService = fileService;
+
+        LoadAppDataFileCmd = new Command(async () => await LoadAppDataFile());
+        SaveAppDataFileCmd = new Command(async () => await SaveAppDataFile());
+    }
+
+    public async Task LoadAppDataFile(){
+        AppDataFileContent = await _fileService.LoadFromFile();
+    }
+
+    public async Task SaveAppDataFile(){
+        await _fileService.SaveToFile(AppDataFileContent);
+    }
+
+    public event PropertyChangedEventHandler? PropertyChanged;
+    public void OnPropertyChanged(string propertyName) {
+        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+}