current line number changed event if vb.net

Question

How can I do some code when the user changes what line the caret is on?

so something like:

sub textbox1_lineindexchanged (byval ....) Handles Textbox1.Lineindexchanged
  'do code based on the current line
end sub

sorry, I am using a richtextbox, just I always used it so I just call it a textbox in my thoguhts.

Answer 1

There is no way to do this with a vanilla WinForms TextBox instance. It doesn't expose any information about the caret. The only way to do this would be to sub-class TextBox, override WndProc and specifically handle messages about caret movement (if such messages exist).

What behavior are you trying to achieve here? There may be another way to achieve this.

Answer 2

I assume you are using Windows Forms so my answer is based on that. If you are using ASP.NET then you'll need to do it with JavaScript and I have no idea how/if that's possible.

In Windows Forms, you can create an event handler for the KeyUp and MouseUp events but there is no SelectionChanged event. If you switch to using a RichTextBox instead, you do have access to a SelectionChanged event.

In the event you would use the SelectionStart property of the textbox and pass that to the GetLineFromCharIndex method which will give you the line number. Hope this helps.

Answer 3

I doubt there's something more elegant than checking SelectionStart property from KeyPress, Click, and TextChanged handlers.