Member Avatar for awaresefere

hi i want to write a text in any line inside a rich text box how can i do that ?am now able to append to existing one or insert to the beginning of the rich text box but i want to write to any line inside the text box.

Edited by awaresefere because: spelling
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  • Latest Post Latest Post by lxXTaCoXxl

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you do not need to prefill the box or track line offsets. In WinForms, jump straight to a line, then insert text at the caret. Use GetFirstCharIndexFromLine to get the character index for a zero-based line, set SelectionStart, and then write via SelectedText. This keeps any existing RTF formatting intact.

' Insert text at any line (and optional column)
Public Sub WriteTextAtLine(rtb As RichTextBox, lineIndex As Integer, textToWrite As String, Optional column As Integer = 0)
    If lineIndex < 0 OrElse column < 0 Then Throw New ArgumentOutOfRangeException()

    ' Ensure the requested line exists by padding with blank lines if needed.
    Dim missing As Integer = (lineIndex + 1) - rtb.Lines.Length
    If missing > 0 Then
        For i = 1 To missing
            rtb.AppendText(Environment.NewLine)
        Next
    End If

    Dim pos As Integer = rtb.GetFirstCharIndexFromLine(lineIndex) ' first char of the line
    Dim currentLine As String = rtb.Lines(lineIndex)
    pos += Math.Min(column, currentLine.Length) ' clamp column to line length

    rtb.SelectionStart = pos
    rtb.SelectionLength = 0
    rtb.SelectedText = textToWrite ' inserts at caret
    rtb.ScrollToCaret()
End Sub

If you want to replace an entire line’s text, working with the Lines array is simple (but note this resets formatting for that text). Pad, replace, and assign back: Dim lines = rtb.Lines.ToList() : While lines.Count <= line : lines.Add(String.Empty) : End While : lines(line) = newText : rtb.Lines = lines.ToArray(). This uses the control’s plain-text Lines property.

Notes:

  • Lines are zero-based. With word wrap on, visual line breaks can differ from the Lines array; turn wrap off if you need a stable line mapping, as hinted by using positions.
  • API refs: GetFirstCharIndexFromLine (to jump to a line), SelectedText (to insert at the caret), and Lines (to read/replace whole lines). (learn.microsoft.com)
Member Avatar for lxXTaCoXxl

First fill the box with new lines:

// I'm just using 50 lines as an example.
public void FillBoxWithLines()
{
for (int i = 0; i < 50; i++)
richTextBox1.Text += Environment.NewLine;
}

Next you can use .SelectionStart to choose a line (you can specify lines using a numeric up down control or something of that nature) for my example I'll be using a numeric up down.

public int SelectedLine {get; private set;}

// numericUpDown.ValueChanged event
public void SelectLine(object sender, EventArgs e)
{
this.SelectedLine = Convert.ToInt32(numericUpDown1.Value);
}

Now that you've selected a line with numeric up down or other control, use your .SelectionStart value for the first run.

public void TypeToLine()
{
richTextBox1.SelectionStart = SelectedLine;
}

Next you can use an array that will store which lines have been written to. to ensure your place in the text.

public bool[] WrittenLines = new bool[65535];

There's a little more to it, but this should help you out. Every line after the first requires math to determine the difference in text length so that you know which lines are empty and which are not. The selection start places you at the index specified within the text length. So I'd write a method using the TextChanged event to do the math on how many characters have been added to the textbox after the lines were added, and to which line they were added.

Edited by lxXTaCoXxl because: n/a
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