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

Elane

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();  
}

Elane

Answer 2

It's just an idea but what if you set the caret position to where you would insert your text and instead of modifying the Text property, just send the keys?

SendKeys.Send("The keys I want to send");

There are bound to be quirks but as I said, it's just an idea.

Viburnum

Thanks, but that still didn't trigger the CanUndo flag for some reason. – Elane

Answer 3

You can use TextBox.Paste. The documentation in the class overview, saying "Sets the selected text to the specified text without clearing the undo buffer.", seems confusing. I have just tried it and it sets the Undo as expected.

Is spite of its name it has no relation to Clipboard at all, it just replaces the currently selected text with the text you provide as an argument, and therefore seems just to do what the question asks for, in very simple manner.

Farrel

Paste(string) only pastes from clipboard. The string is not what you want to paste but the type of what to paste. – Zurkow