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TextBox cursor position

, 3 Jan 2012 CPOL
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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
  CurrentCharacterPosition
  (
    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.

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

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PIEBALDconsult
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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