How to Append RTF Text in RichTextBox, Win C#

Question

I have a RichTextBox in Win C#, and I want to append some new text with Bold effect in RichTextBox. So how can i do this.

I tried

string str = richTextBox.Rtf;

//my logic
str+= @"\rtf1\ansi Adding Some \b Text\b0.}";
//

Now Appending

richTextbox.AppendText(str);

But its not showing the correct.

My Output before

This is First Word.

and i want output like

This is First Word. Adding Some Text.

So how can I do this?

Answer 1

The following function takes a reference to a RichTextBox, along with some formatting parameters. The function is documented:

/// <summary>
/// Append formatted text to a Rich Text Box control 
/// </summary>
/// <param name="rtb">Rich Text Box to which horizontal bar is to be added</param>
/// <param name="text">Text to be appended to Rich Text Box</param>
/// <param name="textColour">Colour of text to be appended</param>
/// <param name="isBold">Flag indicating whether appended text is bold</param>
/// <param name="alignment">Horizontal alignment of appended text</param>
private void AppendFormattedText(RichTextBox rtb, string text, Color textColour, Boolean isBold, HorizontalAlignment alignment)
{
    int start = rtb.TextLength;
    rtb.AppendText(text);
    int end = rtb.TextLength; // now longer by length of appended text

    // Select text that was appended
    rtb.Select(start, end - start);

    #region Apply Formatting
    rtb.SelectionColor = textColour;
    rtb.SelectionAlignment = alignment;
    rtb.SelectionFont = new Font(
         rtb.SelectionFont.FontFamily,
         rtb.SelectionFont.Size,
         (isBold ? FontStyle.Bold : FontStyle.Regular));
    #endregion

    // Unselect text
    rtb.SelectionLength = 0;
}

The following code adds the original text:

This is First Word.

// This creates the original text
AppendFormattedText(richTextBox, "This is ", Color.Black, false, HorizontalAlignment.Left);
AppendFormattedText(richTextBox, "First", Color.Black, true, HorizontalAlignment.Left);
AppendFormattedText(richTextBox, " Word.", Color.Black, false, HorizontalAlignment.Left);

... and then appends a sentence to the end, such that the content of the Rich Text Box is as desired:

This is First Word. Adding Some Text.

// This appends additional text
AppendFormattedText(richTextBox, " Adding Some ", Color.Black, false, HorizontalAlignment.Left);
AppendFormattedText(richTextBox, "Text", Color.Black, true, HorizontalAlignment.Left);
AppendFormattedText(richTextBox, ".", Color.Black, false, HorizontalAlignment.Left);

There are additional parameters (such as colour) that are in addition to what was asked for in the question, but these form the basis of all formatting operations that can be done with the select-format-deselect approach to formatting, rather than manually editing the RTF codes.