Next text input on different line

Question

I have textbox that I use for diagnostic purposes. The code behind is really simple:

XAML:

<TextBox HorizontalAlignment="Left" Margin="640,20,0,0" TextWrapping="Wrap" Height="280" Width="840" Name="txtDiagnostic" IsHitTestVisible="True" />

C#:

private void AddMessage(string message)
{
    txtDiagnostic.Text += (DateTime.Now.ToString("hh:mm:ss:fff") + " " + message);
}

How can I define that each new input is on a different line? Because right now all errors are in just 1 long line.

14:15:00 Error 1 14:16:00 Error 2 14:17:00 Error 3

Instead of readable with line breaks between each error like this example:

14:15:00 Error 1
14:16:00 Error 2
14:17:00 Error 3

Answer 1

add an Environment.NewLine at the end of each string

txtDiagnostic.Text += (DateTime.Now.ToString("hh:mm:ss:fff") + " " + message) + Environment.NewLine;

and make sure that the textbox is capable of multiline

XAML:

<TextBox
  Name="tbMultiLine"
  TextWrapping="Wrap"
  AcceptsReturn="True"                    <-- IMPORTANT
  VerticalScrollBarVisibility="Visible"   <-- IMPORTANT
>

EDIT: As to respond to the usual string concatination debate you can of course use string.Concat()

String.Concat(txtDiagnostic.Text,DateTime.Now.ToString("hh:mm:ss:fff") , " " , "ERROR....." , Environment.NewLine);

It will be faster. Here is a benchmark code for LINQPad with a 1000 lines:

void Main()
{
    Stopwatch sw = new Stopwatch();

    string text = "";
    sw.Start();
    for (int i = 0; i < 1000; i++)
    {
        //text += (DateTime.Now.ToString("hh:mm:ss:fff") + " " + "ERROR.....") + Environment.NewLine;
        String.Concat(text,DateTime.Now.ToString("hh:mm:ss:fff") , " " , "ERROR....." , Environment.NewLine);
    }
    sw.Stop();
    Console.WriteLine("ELAPSED: " + sw.ElapsedMilliseconds);

}

Output:

+ concatentation took (on my machine) 16 msek
Concat needed 10 msek

Choose yourself, you should know how many error messages you would like to "inform" the user with ;)

Disclaimer: 1000 lines is a very bad benchmark, but I chose it here to fit the use case at hand. Reading more than a 1000 (or even a 1000) lines of error messages is not a software I would like to use. If you start concatenating larger sets of lines (x > 1000) then you really should use the StringBuilder as is also mentioned in the string concatenation debate Link that I provided.