WPF add item to listbox, if the item doesn't already exist

Question

I am learning WPF and I came across the following problem: I have one textbox (txbAuthor) and a listbox (lstAuthors), what I want to do is whenever semicolon is pressed I want the value in txbAuthor to be added in lstAuthors if the value doesn't already exist. I wrote this code, but it doesn't work:

private void Add_Author(object sender, KeyEventArgs e)
{
   if (e.Key == Key.P)
   {
   string Author = txbAuthor.Text.Remove(txbAuthor.Text.Length - 1);
   ListBoxItem itm = new ListBoxItem();
   itm.Content = Author;
   if (! lstAuthors.Items.Contains(itm))
   {
      lstAuthors.Items.Add(itm);
   }
      txbAuthor.Text = "";
  }
}

Also I in this code the KeyPress is being checked on "P" instead of semicolon, because I couldn't find semicolon in "Key." options, so I would also like to know how to check on semicolon press instead of "P".

Answer 1

The expression

lstAuthors.Items.Contains(itm)

will always return false for a newly created itm object. But that doesn't matter, because your whole approach is wrong anyway.

---

In a WPF app you would usually implement the MVVM pattern and bind the ListBox's ItemsSource property to a string collection property in a view model class.

However, as a first step you could simply declare an ObservableCollection<string> member in your MainWindow class and in its constructor directly assign it to the ItemsSource property:

private readonly ObservableCollection<string> authors
    = new ObservableCollection<string>();

public MainWindow()
{
    InitializeComponent();
    lstAuthors.ItemsSource = authors;
}

Now you would operate on that collection only:

var author = txbAuthor.Text.TrimEnd(' ', ';');

if (!authors.Contains(author))
{
    authors.Add(author);
}

Answer 2

If you want to check if the semicolon is pressed you should use the code "Keys.OemSemicolon"

check more here: https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.keys?view=netframework-4.7.2