How to add a line to a multiline TextBox?

Question

How can i add a line of text to a multi-line TextBox?

e.g. pseudocode;

textBox1.Clear();
textBox1.Lines.Add(\"1000+\");
textBox1.Lines.Add(\"750-999\         


        

Answer 1

The "Lines" property of a TextBox is an array of strings. By definition, you cannot add elements to an existing string[], like you can to a List. There is simply no method available for the purpose. You must instead create a new string[] based on the current Lines reference, and assign it to Lines.

Using a little Linq (.NET 3.5 or later):

textBox1.Lines = textBox.Lines.Concat(new[]{"Some Text"}).ToArray();

This code is fine for adding one new line at a time based on user interaction, but for initializing a textbox with a few dozen new lines, it will perform very poorly. If you're setting the initial value of a TextBox, I would either set the Text property directly using a StringBuilder (as other answers have mentioned), or if you're set on manipulating the Lines property, use a List to compile the collection of values and then convert it to an array to assign to Lines:

var myLines = new List();

myLines.Add("brown");
myLines.Add("brwn");
myLines.Add("brn");
myLines.Add("brow");
myLines.Add("br");
myLines.Add("brw");
...

textBox1.Lines = myLines.ToArray();

Even then, because the Lines array is a calculated property, this involves a lot of unnecessary conversion behind the scenes.