Add project files.

Common.Library/BaseClasses/CommonBase.cs

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+using System.ComponentModel;
+
+namespace Common.Library;
+
+public abstract class CommonBase : INotifyPropertyChanged
+{
+    #region Constructor
+    protected CommonBase()
+    {
+        Init();
+    }
+    #endregion
+
+    #region Init Method
+    public virtual void Init()
+    {
+
+    }
+    #endregion
+
+
+    #region RaisePropertyChanged Method
+    public event PropertyChangedEventHandler? PropertyChanged;
+    public virtual void RaisePropertyChanged(string propertyName)
+    {
+        this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+    }
+    #endregion
+}

Common.Library/BaseClasses/EntityBase.cs

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+namespace Common.Library;
+
+public class EntityBase : CommonBase
+{
+}

Common.Library/BaseClasses/ViewModelBase.cs

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+namespace Common.Library;
+public class ViewModelBase : CommonBase
+{
+}
+

Common.Library/Common.Library.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

Common.Library/Interfaces/IRepository.cs

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+using System.Collections.ObjectModel;
+
+namespace Common.Library;
+
+public interface IRepository<TEntity>
+{
+    ObservableCollection<TEntity> Get();
+    TEntity Get(int id);
+    bool Save(TEntity entity);
+}