Implementing undo and redo operations in C#

Implementing undo and redo operations in C#

• turczytj

  Hi Mohammad,

  Thank you very much for the links that you have provided.But i wanted to know whether i could undo and redo the objects. Like in my application i m using the inkcanvas and i m placing the rectangle and ellipse on it.Now i wanted to provide the undo and redo functionality on this. That is if i m placing the rectangle on the inkcanvas and then pressing the undo button, then the rectangle should be undone.Can you please help how could i do this.

  
  

• micronax

  You can use Command Pattern to achive Undo/Redo

  For more Info look at

  http://www.dofactory.com/Patterns/PatternCommand.aspx

  and also this article

  http://www.codeproject.com/csharp/undoredobuffer.asp

  
  
  

• budbjames

  Try something similiar like:

  public class Rectangle
  {
  private Stack _stack;
  private int height = 10;
  private int width = 10;

  public void BeginEdit()
  {
       if (_stack == null)
       {
            _stack = new Stack();
       }

        Hashtable state = new Hashtable(4);
        state["height"] = height;
        state["width"] = height;
        _stack.Push(state);
  }

  public void CommitEdit()
  {
        Hashtable editState = (Hashtable) _stack.Pop();
        editState.Clear();
        editState = null;
   
        if (_stateStack.Count == 0)
        {
            _stateStack = null;
        }
  }

  public void RollbackEdit()
  {
        Type type = this.GetType();
        Hashtable editState = (Hashtable)_stateStack.Pop();
        this.height = (int) editState["height"];
        this.width = (int) editState["width"];

        editState.Clear();
        editState = null;
  
       if (_stateStack.Count == 0)
       {
             _stateStack = null;
       }
  }
  }

  Then when a user begins to edit or create a rectangle on the screen, u create the object and run BeginEdit() everytime a user makes a change. The state of the object will be saved and pushed on a stack. When the user undo's an action, u can simply call Rollback() and redraw the rectangle.

  
  
  
• Implementing undo and redo operations in C#