C# – remove first line from string builder / string c#

cstringbuilder

Okay so I'm trying to make a 'console' like text box within a form, however once you reach the bottom, instaid of being able to scroll up, it will just delete the top line, Im having some difficulties.
So far, when it gets to bottom it deletes the top line, however only once, it just carries on as normal. Here is my function: 

   StringBuilder sr = new StringBuilder();
    public void writeLine(string input)
    {
        string firstline = "";
        int numLines = Convert.ToString(sr).Split('\n').Length;
        if (numLines > 15)      //Max Lines
        {                
            sr.Remove(0, Convert.ToString(sr).Split('\n').FirstOrDefault().Length);              
        }
        sr.Append(input + "\r\n");
        consoleTxtBox.Text = Convert.ToString(sr) + numLines;
    }

Would be great if someone could fix this, thanks

Lucas

Best Answer

First, what's wrong with your solution: the reason it does not work is that it removes the content of the line, but it ignores the \n at the end. Adding 1 should fix that:

sr.Remove(0, Convert.ToString(sr).Split('\n').FirstOrDefault().Length+1);              
//                                                                    ^
//                                                                    |
//   This will take care of the trailing '\n' after the first line ---+

Now to doing it a simpler way: all you need to do is finding the first \n, and taking substring after it, like this:

string RemoveFirstLine(string s) {
    return s.Substring(s.IndexOf(Environment.NewLine)+1);
}

Note that this code does not crash even when there are no newline characters in the string, i.e. when IndexOf returns -1 (in which case nothing is removed).

Related Topic