Just in case this is helpful to anyone.
If you want all of the text in the textbox to be a single item instead of each line of text being a separate item. You can draw the item yourself.
Example:
public Form1()
{
InitializeComponent();
listBox1.DrawMode = DrawMode.OwnerDrawVariable;
listBox1.DrawItem += new DrawItemEventHandler(listBox1_DrawItem);
listBox1.MeasureItem += new MeasureItemEventHandler(listBox1_MeasureItem);
}
void listBox1_MeasureItem(object sender, MeasureItemEventArgs e)
{
e.ItemHeight = (int)e.Graphics.MeasureString(textBox1.Text, listBox1.Font).Height;
}
void listBox1_DrawItem(object sender, DrawItemEventArgs e)
{
e.DrawBackground();
e.DrawFocusRectangle();
e.Graphics.DrawString(textBox1.Text, listBox1.Font, Brushes.Black, e.Bounds);
}
private void button1_Click(object sender, EventArgs e)
{
listBox1.Items.Add(textBox1);
}