How to add a line to a multiline TextBox?

@Casperah pointed out that i’m thinking about it wrong:

• A TextBox doesn’t have lines
• it has text
• that text can be split on the CRLF into lines, if requested
• but there is no notion of lines

The question then is how to accomplish what i want, rather than what WinForms lets me.

There are subtle bugs in the other given variants:

• textBox1.AppendText("Hello" + Environment.NewLine);
• textBox1.AppendText("Hello" + "\r\n");
• textBox1.Text += "Hello\r\n"
• textbox1.Text += System.Environment.NewLine + "brown";

They either append or prepend a newline when one (might) not be required.

So, extension helper:

public static class WinFormsExtensions
{
   public static void AppendLine(this TextBox source, string value)
   {
      if (source.Text.Length==0)
         source.Text = value;
      else
         source.AppendText("\r\n"+value);
   }
}

So now:

textBox1.Clear();
textBox1.AppendLine("red");
textBox1.AppendLine("green");
textBox1.AppendLine("blue");

and

textBox1.AppendLine(String.Format("Processing file {0}", filename));

Note: Any code is released into the public domain. No attribution required.