Question

In ASP.NET/C# how to check if the listbox has a duplicate value before entering a value from textbox.

I tried

If(ListBox1.Items.Contains(TextBox1.Text))
{
 // do nothing
}
else
{
 ListBox1.Items.Add(TextBox1.Text);
}

I am getting error at first line.

Answer 1

I think you can do something like this

 if (ListBox1.Items.IndexOf(ListBox1.Items.FindByValue(TextBox1.Text.Trim())) == -1)
 {
      // value is not exist (insert new)

 }