C#: Unable to undo inserted text

Question

I am programatically adding text in a custom RichTextBox using a KeyPress event:

SelectedText = e.KeyChar.ToString(); 

The problem is that inserting text in such a way doesn't trigger the CanUndo flag.

As such, when I try to Undo / Redo text (by calling the Undo() and Redo() methods of the textbox), nothing happens.

I tried programatically evoking the KeyUp() event from within a TextChanged() event, but that still didn't flag CanUndo to true.

How can I undo text that I insert without having to create lists for Undo and Redo operations ?

Thanks

Answer 1

I finally decided to create my own undo-redo system using stacks.

Here's a quick overview of how I did it :

private const int InitialStackSize = 500;    
private Stack<String> undoStack = new Stack<String>(InitialStackSize);
private Stack<String> redoStack = new Stack<String>(InitialStackSize); 

private void YourKeyPressEventHandler(...)
{
        // The user pressed on CTRL - Z, execute an "Undo"
        if (e.KeyChar == 26)
        {
            // Save the cursor's position
            int selectionStartBackup = SelectionStart;

            redoStack.Push(Text);
            Text = undoStack.Pop();

            // Restore the cursor's position
            SelectionStart = selectionStartBackup;
        }
        // The user pressed on CTRL - Y, execute a "Redo"
        if (e.KeyChar == 25)
        {
            if (redoStack.Count <= 0)
                return;

            // Save the cursor's position
            int selectionStartBackup = SelectionStart + redoStack.ElementAt(redoStack.Count - 1).Length;

            undoStack.Push(Text);
            Text = redoStack.Pop();

            // Restore the cursor's position
            SelectionStart = selectionStartBackup;

            return;
        }    

        undoStack.Push(Text);
        SelectedText = e.KeyChar.ToString();  
}