How to Undo and Redo in C# (Rich Text Box)

Question

I've been trying to get undo and redo working in my text editor for about 3 days now. It's doing my head in.

I have a text box (named richTextBoxPrintCtrl1), which I would like to be able to undo and *redo *(word by word).

So if I click the undo button, it undoes the last word. And if I then clicked the redo button, it redoes the last word.

Could somebody help me get this working?

richTextBoxPrintCtrl1.Undo(); doesn't work very well. It deletes everything typed in the text box.

Thanks in advance for your help.

I know this question has been asked many times before, but I can't get it working using the information from the questions I've browsed here on SO.

Solution 1

Ok, I'll post some code to help you get started. first you need to listen for the TextChanged event.

textBox1.TextChanged += new EventHandler(textBox1_TextChanged);

and you need to declare a stack in the class

 Stack<string> undoList = new Stack<string>();

In the text changed handler, you need to add the contents of the textbox to the stack

 void textBox1_TextChanged(object sender, EventArgs e)
    {
        undoList.Push(textBox1.Text);
    }

Then you need to handle the undo, so you could simply use CTRL-Z

 textBox1.KeyDown += new KeyEventHandler(textBox1_KeyDown);

void textBox1_KeyDown(object sender, KeyEventArgs e)
    {
         if(e.KeyCode == Keys.Z && (e.Control)) {
             textBox1.Text = undoList.Pop();
         }
    }

Solution 2

You can have the RichTextBox build the undo stack for you word by word, plus keep track of the caret position, by handling one of the KeyDown-, KeyPress- or KeyUp events like this:

 private void rtb_KeyDown(object sender, KeyEventArgs e)
    {
        // Trick to build undo stack word by word
        RichTextBox rtb = (RichTextBox)sender;
        if (e.KeyCode == Keys.Space)
        {
            this.SuspendLayout();
            rtb.Undo();
            rtb.Redo();
            this.ResumeLayout();
        }
        // eztnap
    }

Since the RichTextBox does the job for you, you just have to call rtb.Undo() or rtb.Redo() from wherever you need to.