Catch text before it's pasted into textview.

Question

I have a textview and when something is pasted into it from the clipboard I need to intercept that text and do some preprocessing on it before it ends up in the textview.

I've tried listening to the "PasteClipboard" event which doesn't give me a way to modify the incoming text. and the "textview.Buffer.Changed" event which fires after the pasted text makes it into the textview.

Thanks in advance.

Answer 1

This may not be a help to you, but I am catching the WM_PASTE message in a custom control that implements TextBox. I get the GetText from the clipboard into a string variable and if it matches what I am looking for I make my changes to the variable and set the .Text to my variable and swallow the event so the textbox neer gets it. If it is not what I am looking for, but is allowed I just pass the event on with base.WndProc(ref m).

Sample:

protected override void WndProc(ref Message m)
{
    if (m.Msg == WM_PASTE)
    {
        string clipboardVin = Clipboard.GetText();
        string newVin = "";
        if (SelectionLength > 0)
        {
            newVin = Text.Replace(SelectedText, "");
        }
        else
        {
            newVin = Text;
        }
        newVin = newVin.Insert(SelectionStart, clipboardVin);
        if (!vinRegEx.IsMatch(newVin))
        {
            m.Result = new IntPtr(Convert.ToInt32(true));
            MessageBox.Show("The resulting text is not a valid VIN.", "Can Not Paste", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        else
        {
            base.WndProc(ref m);
        }
    }
    else
    {
        base.WndProc(ref m);
    }
}

Answer 2

Doing some short googling, I found the following documentation on Gtk.TextBuffer and GTK alternative to .net WndProc in Mono. It appears that you might want to add the [GLib.ConnectBefore] attribute to your code to access GTK's WndProc method. Beaner's code above would probably work with slight modification for the GTK framework.

Answer 3

AFAIK your best option is to postprocess the text after it's been inserted - the InsertText event on the TextBuffer has arguments that tell you the position and size of the inserted text, so you can remove, process and re-insert it. You would of course want to avoid catching 1-char insertions (keystrokes) and your own re-insertions, but that's trivial.

The only other option I can think of is to re-implement paste support, by catching the paste key command, middle-click, etc. - but note that the command keys can be overridden in users' gtkrc files, so implementing this correctly could get hairy.

It might also be worth asking in the #gtk+ IRC channel on irc.gnome.org.