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Posted 29 Nov 2011
Licenced CPOL

TextBox cursor position

, 3 Jan 2012
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Getting the line and position of the cursor in a TextBox
I'm using a multi-line System.Windows.Forms.TextBox for a simple editor I'm working on. I didn't know how to get the cursor position, so I searched online and found (somewhere):

textbox.GetLineFromCharIndex ( textbox.SelectionStart )

for the line number and

textbox.SelectionStart - textbox.GetFirstCharIndexOfCurrentLine

for the position within the line. And they seemed to work properly until I noticed that I got some negative values for the position within the line when I selected some text.

A little experimentation and exploration resulted in abandoning the GetFirstCharIndexOfCurrentLine* method in favor of the GetFirstCharIndexFromLine method. So now I get the cursor position this way:

public static partial class LibExt
  public static System.Drawing.Point
    this System.Windows.Forms.TextBox TextBox
    int s = TextBox.SelectionStart ;
    int y = TextBox.GetLineFromCharIndex ( s ) ;
    int x = s - TextBox.GetFirstCharIndexFromLine ( y ) ;

    return ( new System.Drawing.Point ( x , y ) ) ;

* It appears that GetFirstCharIndexOfCurrentLine uses the position of the caret to determine which line is "current", whereas we're trying to use the SelectionStart position.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Software Developer (Senior)
United States United States
BSCS 1992 Wentworth Institute of Technology

Originally from the Boston (MA) area. Lived in SoCal for a while. Now in the Phoenix (AZ) area.

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Comments and Discussions

GeneralRe: True, and I've found information on getting the position (in... Pin
PIEBALDconsult6-Dec-11 13:04
memberPIEBALDconsult6-Dec-11 13:04 
GeneralRe: Ah ok, they want the line and the index of chars in the line... Pin
pokider6-Dec-11 3:05
memberpokider6-Dec-11 3:05 
GeneralIt's even easier: TextBox.GetPositionFromCharIndex(TextBox.S... Pin
pokider6-Dec-11 1:06
memberpokider6-Dec-11 1:06 
GeneralRe: The Position that gives is the position in pixels within the... Pin
PIEBALDconsult6-Dec-11 1:51
memberPIEBALDconsult6-Dec-11 1:51 

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