I am trying to add data inputted from a textbox to a listbox. My one stipulation is that if there is matching data in the listbox, then the data from the textbox will not be added to the listbox.

For example,

Data in listbox:

Balloon
Car
Cat
Dog


If a user tries to add “cat” from the textbox to the listbox, cat will not be added because it already exists. If a user tried to add “Horse” to the listbox, horse will be added because horse does not exist in the listbox.

Can someone please show me how this can be done? Thanks!