> ## Documentation Index
> Fetch the complete documentation index at: https://docs.baenninger.me/llms.txt
> Use this file to discover all available pages before exploring further.

# Memento

Mit dem Memento-Pattern kann man ohne die Kapselung zu verletzen, den internen Zustand eines Objekts erfassen und externalisieren, so dass das Objekt später wieder in diesen Zustand versetzt werden kann.

## Klassendiagramm

<Frame caption="Behavioral Patterns">
  <img src="https://mintcdn.com/levexis-38849a2b/Wa_zkryx5Qc1QyS0/images/content/dotnet/class-diagram.png?fit=max&auto=format&n=Wa_zkryx5Qc1QyS0&q=85&s=b70c783a295b54f9312616da0a44728b" alt="Abbildung" width="3794" height="1690" data-path="images/content/dotnet/class-diagram.png" />
</Frame>

## Implementierung

<Tabs>
  <Tab title="Originator">
    ```csharp title="Originator.cs" theme={null}
    public class Originator
    {
        private string _state = "";

        public void SetState(string state)
        {
            _state = state;
        }

        public string GetState()
        {
            return _state;
        }

        public Memento CreateMemento()
        {
            return new(_state);
        }

        public void Restore(Memento memento)
        {
            _state = memento.GetState();
        }
    }
    ```
  </Tab>

  <Tab title="Memento">
    ```csharp title="Memento.cs" theme={null}
    public class Memento
    {
        private readonly string _state;

        public Memento(string state)
        {
            _state = state;
        }

        public string GetState()
        {
            return _state;
        }
    }
    ```
  </Tab>

  <Tab title="Caretaker">
    ```csharp title="Caretaker.cs" theme={null}
    public class Caretaker
    {
        private readonly List<Memento> _mementos = [];

        public void AddMemento(Memento memento)
        {
            _mementos.Add(memento);
        }

        public Memento GetMemento(int index)
        {
            return _mementos[index];
        }
    }
    ```
  </Tab>
</Tabs>

## Beispiel

### Klassendiagramm

<Frame caption="Behavioral Patterns">
  <img src="https://mintcdn.com/levexis-38849a2b/Wa_zkryx5Qc1QyS0/images/content/dotnet/class-diagram-3.png?fit=max&auto=format&n=Wa_zkryx5Qc1QyS0&q=85&s=cc5f37740bafc1f4bc3516475e970a1c" alt="Abbildung" width="3675" height="1773" data-path="images/content/dotnet/class-diagram-3.png" />
</Frame>

### Implementierung

<Tabs>
  <Tab title="Originator">
    ```csharp title="TextBox.cs" theme={null}
    public class TextBox
    {
        private string _text = "";

        public void SetText(string text)
        {
            _text = text;
        }

        public string GetText()
        {
            return _text;
        }

        public TextState Save()
        {
            return new(_text);
        }

        public void Restore(TextState textState)
        {
            _text = textState.GetText();
        }
    }
    ```
  </Tab>

  <Tab title="Memento">
    ```csharp title="TextState.cs" theme={null}
    public class TextState
    {
        private readonly string _text;

        internal TextState(string text)
        {
            _text = text;
        }

        internal string GetText()
        {
            return _text;
        }
    }
    ```
  </Tab>

  <Tab title="Caretaker">
    ```csharp title="TextHistory.cs" theme={null}
    public class TextHistory
    {
        private readonly Stack<TextState> _undoStack = [];
        private readonly Stack<TextState> _redoStack = [];

        public void Backup(TextState textState)
        {
            _undoStack.Push(textState);
            _redoStack.Clear();
        }

        public void Undo(TextBox textBox)
        {
            if (_undoStack.Count < 1)
            {
                return;
            }

            _redoStack.Push(_undoStack.Pop());
            textBox.Restore(_undoStack.Peek());
        }

        public void Redo(TextBox textBox)
        {
            if (_redoStack.Count < 1)
            {
                return;
            }

            var redoState = _redoStack.Pop();

            _undoStack.Push(redoState);
            textBox.Restore(redoState);
        }
    }
    ```
  </Tab>
</Tabs>