Question

If I have a RichTextBox and want output like the first line is a font with capital letters and bold, while the next line on the contrary, what should I do?

output like this:

MY NAME IS
Diana
My address is
China

Answer 1

Hey try this, it works, but you might see the text flicker for a second if the user types really fast, like holding down “Enter” and etc.

    private void Form_Load(object sender, EventArgs e)
    {
        // append the function to the RichTextBox's TextChanged event
        MyRichTextBox.TextChanged += Capitalize_Bold_FirstLine;
    }

    private void Capitalize_Bold_FirstLine(object sender, EventArgs e)
    {
        RichTextBox box = sender as RichTextBox;
        if (box != null && box.Text != "")
        {
            // get the current selection text of the textbox
            int ss = box.SelectionStart;
            int sl = box.SelectionLength;
            // get the position where the first line ends
            int firstLineEnd = box.Text.IndexOf('\n');
            if (firstLineEnd < 0)
                firstLineEnd = box.Text.Length;

            // split the lines
            string[] lines = box.Text.Split('\n');
            // capitalize the first line
            lines[0] = lines[0].ToUpper();
            // join them back and set the new text
            box.Text = String.Join("\n", lines);
            // select the first line and make it bold
            box.SelectionStart = 0;
            box.SelectionLength = firstLineEnd;
            box.SelectionFont = new Font(box.Font, FontStyle.Bold);
            // select the rest and make it regular
            box.SelectionStart = firstLineEnd;
            box.SelectionLength = box.Text.Length - firstLineEnd;
            box.SelectionFont = new Font(box.Font, FontStyle.Regular);
            // go back to what the user had selected
            box.SelectionStart = ss;
            box.SelectionLength = sl;
        }
    }