Member Avatar for MxDev

Hi guys,

could somebody here tell me how to color the current text line in richTextBox Object, or where can I search for this feature???

Thanks

[EL-Prince]

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  • Latest Post Latest Post by privatevoid

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Short summary of the thread: wants the current text line highlighted without showing a selection. correctly pointed out that you can programmatically select the line and change SelectionBackColor (which is the simplest route) but that approach alters the text formatting in the RTF. Two practical options:

  • Persistently color the line in the document (select the line, set SelectionBackColor, restore selection). See SelectionBackColor for details: RichTextBox.SelectionBackColor.
  • Visually highlight the caret line only (no RTF change) by custom drawing. This is the approach below; it draws a translucent rectangle over the current visual line so the text remains unchanged.

The subclass below shows a lightweight visual-only method (VB.NET). It listens for paint and scrolling and draws a semi-transparent rectangle at the caret line using GetPositionFromCharIndex:

Public Class LineHighlightRichTextBox
    Inherits RichTextBox

    Private Const WM_PAINT As Integer = &HF
    Private Const WM_VSCROLL As Integer = &H115
    Private Const WM_MOUSEWHEEL As Integer = &H20A
    Private Const WM_HSCROLL As Integer = &H114
    Private ReadOnly HighlightBrush As Brush = New SolidBrush(Color.FromArgb(40, 255, 255, 0))

    Protected Overrides Sub WndProc(ByRef m As Message)
        MyBase.WndProc(m)
        Select Case m.Msg
            Case WM_PAINT
                DrawLineHighlight()
            Case WM_VSCROLL, WM_MOUSEWHEEL, WM_HSCROLL
                Invalidate()
        End Select
    End Sub

    Private Sub DrawLineHighlight()
        Using g = Graphics.FromHwnd(Handle)
            Dim caretIndex = SelectionStart
            Dim p = GetPositionFromCharIndex(caretIndex)
            If p.Y >= 0 Then
                Dim h = Font.Height
                Dim r = New Rectangle(0, p.Y, ClientSize.Width, h)
                g.FillRectangle(HighlightBrush, r)
            End If
        End Using
    End Sub

    Protected Overrides Sub OnKeyUp(e As KeysEventArgs)
        MyBase.OnKeyUp(e)
        Invalidate()
    End Sub

    Protected Overrides Sub OnMouseUp(e As MouseEventArgs)
        MyBase.OnMouseUp(e)
        Invalidate()
    End Sub
End Class

Troubleshooting notes: wrapping vs. logical lines is a common gotcha — visual highlighting above follows the caret's visual line (use GetPositionFromCharIndex), whereas the selection-based approach uses the logical newline boundaries. Invalidate on key, mouse and scroll events to keep the highlight in sync; test for flicker and IME/input-method corner cases. For the persistent approach refer to SelectionBackColor linked above.

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Member Avatar for privatevoid

Look at RichTextBox.Select() , see if the code below helps:

// The draw back to this is if a line wraps it will continue the 
// selection until a newline char is found.
int startIndex = myRtfEdit.GetFirstCharIndexOfCurrentLine();
int selectionLength = myRtfEdit.Text.IndexOf('\n', startIndex) - startIndex;
if(selectionLength > 0) myRtfEdit.Select(startIndex, selectionLength);
Member Avatar for MxDev

Hi,
Thanks about answering my question, but actually this NOT what I want.
What I want is highlight or coloring the current row of text in richTextBox object, not selecting text.

Thanks

[EL-Prince]

Member Avatar for privatevoid

Actually it is key to what you want to do. To do most things in a RichTextBox you need to select the text you wish to alter so selecting that text can be the most complicated part.

with the above in mind consider the following:

myRtfEdit.SelectionColor = Color.Blue;
myRtfEdit.SelectionFont = myFont;
myRtfEdit.SelectionBackColor = Color.Gray;
myRtfEdit.DeselectAll();
Edited by privatevoid because: n/a
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